Title of Invention

PROGRAMMABLE DYNAMIC RANGE RECEIVER

Abstract

A programmable dynamic range receiver which provides the requisite level of performance at reduced power consumption. The}:il ADC within the receiver is designed with one or more loops. Each loop provides a predetermined dynamic range performance. The loops can be enabled or disabled based on the required dynamic range and a set of dynamic range thresholds. The E4 ADC is also designed with adjustable bias 'current. The dynamic range of the EADC varies approximately proportional to the bias current. By adjusting the bias current; the required dynamic range can be provided by the }:il ADC with minimal power consumption. A reference voltage of the }:~ ADC can be descreased when high dynamic range is not required, thereby allowing for less bias current in the }:~ ADC and supporting circuitry. The dynamic range of the }:il ADC is a also function of the oversa~pling ratio which is proportional to the sampling frequency. High dynamic range requires a high oversampling ratio. When high dynamic range is not required, the sampling frequency c&n qe lowered.

Full Text

PROGRAMMABLE DYNAMIC RANGE RECEIVER BACKGROUND OF THE INVENTION I. Field of the Invention The present invention relates to communications. More particularly, the present invention relates to a novel and improved programmable dynairtic range receiver. II. Description of the Related Art 'I he design of a high performance receiver is made challenging by various design constraints. First, high performance is required for many applications. High performance can be described by the linearity of the active devices (e.g. amplifiers, mixers, etc.) and the noise figure of the receiver. Second, for some applications such as in a cellular communication system, power consumption is an important consideration because of the portable nature of the receiver. Generally, high performance and high efficiency are conflicting design considerations. An active device has the following transfer function: where x is the input signal, y(\) is the output signal, and aj, a2 and a3 are coefficients which define the linearity of the active device. For simplicity, higher order terms (e.g. terms above third order) are ignored. For an ideal active device, the coefficients a2 and 33 are 0.0 and the output signal is simply the input signal scaled by a1. However, all active devices experience some amount of non linearity which is quantified by the coefficients a1 and a3 Coefficient a2 defines the amount of second order non-linearity and coefficient 33 defines the amount of third order non-linearity. Most communication systems are narrow band systems which operate on an input RF signal having a predetermined bandwidth and center frequency. The input Kb' signal typically comprises olher spurious signals located throughout the frequency spectrum. Non-linearity within the active devices causes intermodulation of spurious signals, resulting in products which may fall into the signal band. The effect of second order non-linearity (e.g. those caused by the \" term) can usually be reduced or eliminated by careful design methodology. Second order non-linearity produces products at the sum and difference frequencies. Typically, the spurious signals which can produce in band second -order products are located far away from the signal band and can be easily filtered. However, third order non-linearity are more problematic. For third order non-linearity, spurious signals x = gi1dos(w1t) Vg2cos(w2t) produce products at the frequencies (2w1-W2) and (2w2-W1). Thus, near band spurious signals (which are difficult to filter) can produce third order intermodillation products falling in-hand, causing degradation in tin; received signal. To compound the problem, the amplitude of the third-order products are scaled by g1 g2 and g1 g2- Thus, every doubling of the amplitude of the spurious signals produces an eight-fold increase in the amplitude of the third order products. Viewed another way, every 1 df$ increase in the input RF signal results in 1 dB increase in the output RI7 signal but 3 dB increase in the third order products. The linearity of a receiver (or the active device) can be characterized by the input-referred third-order intercept point (IIP3). Typically, the output RF signal and the third-order intermodulation products are plotted versus the input RF signal. As the input RF signal is increased, the I1P3 is a theoretical point where the desired output RF signal and the third-order products become equal in amplitude. The IIP3 is an extrapolated value since the active device goes into compression before the I1P3 point is reached. For a receiver comprising multiple active devices connected in cascade, the 1IP3 of the receiver from the first stage of active device to the n stage can be calculated as follows : where IIP3n is the input-referred third order intercept point from the first stage of active device to the n stage, HP3n/j is the input-referred third-order intercept point from the first stage to the (n-1) stage, Avn is the gain of the n stage, III3dn is the input referred third-order intercept point of the n stage, and all terms are given in decibel (dB). The calculation in equation (2) can be carried out in sequential order for subsequent stages within the receiver. From equation (2), it can he observed that one way to improve the ensouled 1113 of the receiver is to lower the gain before the first non-linear active device. However, each active device also generates thermal noise which degrades the signal quality. Since the noise level is maintained at a constant level, the degradation increases as the gain is lowered and the signal amplitude is decreased. The amount of degradation can he measured by the noise figure (NF) of the active device which is given as follows : O) where NI(j is the noise figure of the* active device, SNRin is the signal-to-noise ratio of the input RF signal into the active device, SNRoul is signal-to-•noise ratio of the output RF signal from the active device, and NF(j, SNRin and SNRu.lt are all given in decibel (dR). For a receiver comprising multiple a*live devices connected in cascade, the noise figure of the receiver from the first stage of active device to the n stage can be calculated as follows : (4) where NFa is the noise figure from the first stage to the n stage, NFn„5 is the noise figure of the first stage to the (n-1)th stage, NFjn is the noise figure of the n stage, and Gn.j is the accumulated gain of the first stage through the (n-l)M stage in dB. As shown in equation (4), the gain of the active device can affect the noise figure of the subsequent stages. Similar to the IIP3 calculation in equation (2), the noise figure calculation in equation (4) can he carried out in sequential order tov subsequent stages of the receiver. Receivers are employed for many communication applications, such as cellular communication systems and high definition television (HDTV). Exemplary cellular communication systems include Code Division Multiple Access (CDMA) communication systems. Time Division Multiple Access (fDMA) communication systems, and analog FM communication systems. The use of (DMA techniques in a multiple access communication system is disclosed in U.S. Patent No. 4,001,307, entitled "SPREAD SPECTRUM MUITIPLE: ACCESS COMMUNICATION SYSTEM USING SATELLITE OR IFRRESTR1AE REPEATERS", and U.S. Patent No. 5,103/15, entitled "SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLLIAR TELEPHONE SYSTEM", both assigned to the assigns of the present invention and incorporated by reference herein. An exemplary HDTV system is disclosed in U.S. Patent No. 5,452,104, U.S. Patent No. 5,107,3-15, and U.S. Patent No. 5,021,891, all three entitled "ADAPTIVE BLOCK SIZE IMAGE COMPRESSION METHOD AND SYSTEM", and U.S. Patent No. 5,576,767, entitled "INTERFRAME VIDEO ENCODING AND DECODING SYSTEM", all four patents are assigned to the assignee of the present invention and incorporated by reference herein. In cellular applications, it is common to have more than one communication system operating within the same geographic coverage area. Furthermore, these systems can operate at or near the same frequency band. When this occurs, the transmission from one system can cause degradation in the received signal of another system. CDMA is a spread spectrum communication system which spreads the transmit power to each user over the entire 1.2288 MHz signal bandwidth. The spectral response of an EM -based transmission can be more concentrated at the center frequency. Therefore, FM-based transmission can cause jammers to appear within the allocated CDMA band and very close to the received CDMA signal. Furthermore, the amplitude of the jammers can be many time greater than that of the CDMA signal. These jammers can cause third-order intermodulation products which can degrade the performance of the CDMA system. Typically, to minimize degradation due to intermodulation products caused by jammers, the receiver is designed to have high IIP3. However, design of a high IIP3 receiver requires the active devices within the receiver lo be biased with high DC current, thereby consuming large amounts of power. This design approach is especially undesirable for cellular application wherein the receiver is a portable unit and power is limited. Several techniques have been deployed in the prior art to address the nvvd for high IIP3. One such technique, which also attempts to minimize power consumption, is to implement the gain stage with a plurality of amplifiers connected in parallel and lo selectively enable the amplifiers as higher 11 PI is needed. This technique is disclosed in detail in U.S. Patent Application Serial No. _, entitled "DUAL MODE AMPLIFIER WITH HIGH EFFICIENCY AND INCH LINEARITY", filed , assigned to the assigner of the present invention and incorporated by reference herein. Another technique is to measure the received RF signal power and adjust the gun of the amplifiers based on the amplitude of the RF signal power. This techuique is dreclosed loved in detail in U.S. Patent Application Serial No. An exemplary block diagram of a receiver architecture of the prior art is shown in PIG. 1. Within receiver 1100, the transmitted RF sicnal is t received by antenna 1112, routed through duplexer 1114, and provided to low noise amplifier (l,NA) 1116. LNA 1116 amplifies the RF signal and provides the signal to bandpass filler 1118. Bandpass filter 1118 filters the signal to remove some of the spurious signals which can cause intermodulation products in the subsequent stages. The filtered signal is provided to mixer 1120 which downconverts the signal to an intermediate frequent y (IF) with the sinusoidal from local oscillator 1122. The IF signal is provided to bandpass filter 1124 which filters spurious signals and downconversion products prior to the subsequent downconversion stage. The filtered IF signal is provided to automatic-gain-control (AGC) amplifier 1126 which amplifies the signal with a variable gain to provide an IF signal at the required amplitude. The gain is controlled by a control signal from AGC control circuit 1128. The IF signal is provided to demodulator 1130 which demodulates the signal in accordance with the modulation format used at the transmitter. For digital transmission such as binary phase shift keying (BPSK), quaternary phase shift keying (QPSK), offset quaternary phase shift keying (OQPSK), and quadrature amplitude modulation (QAM), a digital demodulator is used to provide the digitized baseband data. For PM transmission, an FM demodulator is used to provide the analog signal. Receiver 1100 comprises the basic functionalities required by most receivers However, the location of amplifiers 1116 and 1126, bandpass filters 1118 and 1124, and mixer 1120 can be rearranged to optimize the receiver performance for a particular application. In this receiver architecture, high IfP3 is provided for by biasing the active devices a high DC bias current and/or by controlling the gain of amplifier 1126. This receiver architecture has several drawbacks. First, the active devices are typically biased to a high DC current to provide the highest required IIP3. This has the effect of operating receiver 1100 at the high IIP! operating point at all limes, oven though high IIP3 is not required most of the time. Second, the high 1IP3 can be improved by adjusting the gain of AOC amplifier 1126, as disclosed in the aforementioned U.S. Patent No. 5,099,204. However, lowering the gain of amplifier 1126 ran degrade the noise figure of receiver 1100. SUMMARY OF THE INVENTION The present invention is a novel and improved programmable dynamic range receiver which provides the requisite level of performance with reduced power consumption. In the exemplary embodiment, the receiver comprises a front end, a IA ADC, a digital signal processor, a power detector, and an ACC control circuit. In the exemplary embodiment, the inpul KF signal is conditioned and downeonverted into an IF signal by the front end. The IF signal is quantized by the IA ADC to produce IF samples which are processed by the digital signal processor to yield the desired signal. The power detector measures the amplitude of the signal into the IA AFX'. In the exemplary embodiment, the required dynamic range is computed from measurement of the amplitude of the desired signal and the signal into the IA ADC. In the alternative embodiment, the required dynamic range is determined based on the operating mode of the receiver. It is an object of the present invention to provide a programmable dynamic range receiver which minimizes power consumption by enabling and disabling one or more loops within the IA ADC. In the exemplary embodiment, the IA ADC is implemented with one or more loops. Each loop provides a predetermined dynamic range performance. One or more loops within the A ADC can be enabled or disabled as the required dynamic range exceeds or falls below a set of dynamic range thresholds. The dynamic range thresholds can be selected based on numerous considerations, such as the statistics of the input RF signal and the performance of the IA ADC. Furthermore, the dynamic range thresholds can be implemented with hysteresis to prevent toggling of the loops between the enabled and disabled states. It is another object of the present invention to provide a programmable dynamic range receiver which minimizes power consumption by adjustment of the bias current. In the exemplary embodiment, the IA ADC is designed with adjustable bias current. The dynamic range of the I \ ADC varies approximately proportional to the bias current. By adjusting the bias current, the required dynamic range can be provided by the IA ADC with minimal power consumption. The bias current can be adjusted in discrete steps or in continuous manner. It is yet another object of the present invention to provide a programmable dynamic range receiver which minimizes power consumption by adjustment of a reference voltage on the IA ADC. The dynamic range of the 51A ADC1 is determined by the maximum input signal swing and the noise from IA ADC which comprises the circuit noise and the quantization noise. As the required dynamic range decreases, the reference voltage can be lowered while maintaining approximately the same noise level. this is especially true when one loop is switched out and the quantization noise increases such that it is much greater than the circuit noise. By lowering the reference voltage such that the quantization noise is approximately equal to the circuit noise, the desired level of performance is provided while maintaining the signal level at a low level. As an additional benefit, the amplifier driving the IA ADC has a lower maximum signal swing and can be biased with less current. It is yet another object of the present invention to provide a programmable dynamic range receiver which minimizes power consumption by adjustment of the sampling frequency of the ΣA ADC. The dynamic range of the IA ADC is a function of the oversampling ratio which is proportional to the sampling frequency, since the bandwidth of the signal into the ΣA ADC is constant. High dynamic range requires a high Oversampling ratio. The power consumption of the circuits used to implement the IA ADC can be dependent on the sampling frequency. In the present invention, when high dynamic range is not required, the sampling frequency can be lowered to minimize power consumption. It is yet another object of the present invention to provide a programmable dynamic range receiver which minimizes power consumption by switching on the appropriate IA ADC based on the required performance. In this embodiment, the receiver can be designed with two or more IA ADCs which provide the sampling function for two or more operating modes. For example, a receiver can be designed with two ΣA ADCs, one for CDMA mode and one for I;M mode. The IA ADC for the FM mode can be designed to consume significantly less power because of the lower signal bandwidth and the lower required dynamic range. The Appropriate IA ADC can be switched on depending on whether the receiver is operating in the CDMA or FM mode. The features described above can be combined, as appropriate, to provide the required level of performance while maximizing power Savings. BRIEF DESCRIPTION OF THE DRAWINGS The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein: FIG. 1 is a block diagram of an exemplary receiver of the prior art; FIG. 2 is a block diagram of an exemplary programmable linear receiver of the present invention; FIG. 3 is a block diagram of an exemplary programmable linear dual-band receiver of the present invention; FIG. 4 is a block diagram of an exemplary QPSK demodulator which is used within the receivers of the present invention; FTG. 5A-4B are schematic diagrams of an exemplary discrete design of low-noise-amplifier (LNA) and current source which are used in the receivers of the present invention, respectively; FIG. 6A-6B are diagrams of the IIP3 performance versus bias current of the transistor used in the LNA and the performance curves of the LNA, respectively; FIG. 7A-7B are diagrams of the two-tone and single-tone jammers specifications for CDMA signal as defined by IS-98-A, respectively; FIG. 8A-8B are diagrams of the AGC control range for ascending and descending CDMA input power, respectively; FIG. 9 is a diagram of an exemplary IIP3 bias control mechanism of the present invention; FIG. 10A-10B are diagrams of the I1P3 bias control for ascending and descending CDMA input power, respectively; and FIG. 11 is a block diagram of an exemplary two loop bandpass MAS11 IA analog to-digital converter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I he receiver ot the present invention provides the requisite level of system performance1 and minimizes power consumption by controlling the DC bias of the active devices. The present invention can be practiced using one of three embodiments described in detail below. In the first embodiment, the amount of non-linearity at the output of the receiver is measured and used to set the TIP3 operating point of the active devices within the receiver, such as the amplifiers and mixer. In the second embodiment, the IIP3 operating point of the active devices are set in accordance with the expected received signal level based on the operating mode of the receiver. And in the third embodiment, the I1P3 operating point of the active devices are set in accordance with the measured signal level at various stages within the receiver. In the present invention, the AGC function is provided by an AGC control circuit which operates in conjunction with a bias control circuit. The IIP3 operating point of the active devices are set in accordance with the measured amount of non-linearity which is dependent, on the amplitude of the signal. The signal amplitude, in turn, depends on the gain settings of the receiver. In the present invention, the AGC and bias control are operated in an integrated manner to provide the required level of linearity over a specified AGC range while minimizing power consumption. I. Receiver Architecture A block diagram of an exemplary receiver architecture of the present invention is shown in FIG. 2. Within receiver 1200, the transmitted RF signal is received by antenna 1212, routed through duplexer 1214, and provided to attenuator 1216. Attenuator 1216 attenuates the RF signal to provide a signal at the required amplitude and provides the attenuated signal to RF processor 1210. Within RF processor 1210, the attenuated signal is provided to pad 1222a and low noise amplifier (LNA) 1220a. LNA 1220a amplifies the RF signal and provides the amplified signal to bandpass filter 1226. Pad 1222a provides a predetermined level of attenuation and connects in series with switch 1224a. Switch 1224a provides a bypass route around LNA 1220a when the gain of LNA 1220a is not needed. Bandpass filter 1226 filters the signal to remove spurious signals which can cause intermodulation products in the subsequent signal processing stages. The filtered signal is provided to pad 1222b and low noise amplifier (LNA) 1220b. LNA 1220b amplifies the filtered signal and provides the signal to RF/IF processor 1248. Pad 1222b provides a predetermined level of attenuation and connects in series with switch 1224b. Switch 1224b provides a bypass route around I NA 1220b when the gain of LNA 1220b is not needed. Within RF/IF processor 124H, mixer 1230 dow neon verts the signal to an intermediate frequency (IF) with Ihe sinusoidal from local oscillator (I.O) 1228. The Il: signal is provided to bandpass filter 1232 which fillers out spurious signals and out-of band downconversion products. In the preferred embodiment, the filtered IF signal is provided to voltage control amplifier (VGA) 1234 which amplifies the signal with a variable gain which is adjusted by a gain control signal. Amplifier 1234 can also be implemented as a fixed gain amplifier, depending on the system requirement, and this is also within the scope of the present invention. The amplified \V signal is provided to demodulator 1250 which demodulates the signal in accordance with the modulation format used by the transmitter (not shown). RF processor 1210 and Rl'VIF processor 1248 is collectively referred to as a front end. A block diagram of an exemplary demodulator 1250 used for demodulation of quadrature modulated signals (e.g. QPSK, OQrSK, and QAM) is illustrated in FIG. 4. In the exemplary embodiment, demodulator 1250 is implemented as a subsampling bandpass demodulator. The IF signal is provided to bandpass sigrna delta analog-to-digital converter (LA ADC) 1410 which quantizes the signal at a high sampling frequency determined by the CI.K signal. An exemplary design of a ZA ADC is described in detail in U.S. Application Serial No. entitled "SIGMA-DELTA ANALOG-TO- DIGITAL CONVERTER", filed ., and assigned to the assignee of the present invention. The use of a ZA ADC within a receiver is disclosed in copending U.S. Patent Application Serial No. , entitled "RECEIVER WITH SIGMA-DELTA ANALOG-TO-DIGITAL CONVERTER", filed assigned to the assignee of the present invention and incorporated by reference herein. The quantized signal is provided to filter 1412 which filters and decimates the signal. The filtered signal is provided to multipliers 1414a and 1414b which downconvert the signal to baseband with the in-phase and quadrature sinusoids from local oscillator (L02) 1420 and phase shifter 1418, respectively. Phase shifter 1418 provides 90 of phase shift for the quadrature sinusoidal. The baseband I and Q signals are provided to lowpass fillers 1416a and 1416b, respectively, which filler the signal to provide the I and Q data. The baseband data in FIG. 2 comprises the I and Q data in FIG . In the exemplary embodiment, filter 1412 and/or lowpass filters 1416 also provide scaling of the signal to enable demodulator 1250 to provide baseband data at various amplitudes. Other implementations of demodulator 1250 can be designed to performed the demodulation of QPSK modulated waveform and are within the scope of the present invention. Referring hack to IK;. 2, receiver 1200 comprises the basic functionalities required by most receivers. However, the arrangement of attenuator 1216, INAs 1220a am! 1220b, bandpass filters 1226 and 1232, and mixer 1230 can be reordered to optimize the performance of receiver 1200 for specific applications. For example, attenuator 1216 can be interposed between LNA 1220a and bandpass filter 1226 to improve the noise figure performance. Furthermore, a bandpass filter can be inserted before LNA 1220a to remove undesirable spurious signals before the first amplifier stage. Different arrangements of the functionalities shown herein can be contemplated and are within the scope of the present invention. Furthermore, other arrangements of the functionalities shown herein in combination with other receiver functionalities which are known in the art can also be contemplated and are within the scope of the present invention. In the present invention, attenuator 1216, switches 1224a and 1224b, and demodulator 1250 are controlled by AGC control circuit 1260 such that the IF signal from amplifier 1234 is at the required amplitude. The AGC function is described in detail below. In the exemplary embodiment, I.N As 1220a and 1220b are fixed gain amplifiers. LNAs 1220a and 1220b and mixer 1230 are controlled by bias control circuit 1280 to adjust the DC bias current and/or voltages of these active devices such that the required linearity performance is achieved with minimal power consumption. The variable 1IP3 bias control mechanism is described in detail below. The receiver architecture of the present invention can be adopted for use in various applications, including cellular telephone and HDTV applications. In the cellular telephone, receiver 1200 can be adopted for use in CDMA communication systems operating at the personal communication system (PCS) band or the cellular band. A block diagram of an exemplary receiver which supports dual band (PCS and cellular) and dual mode (CDMA and AMPS) is shown in FIG. 3. The PC'S band has a bandwidth of 60 MHz and a center frequency of 1900 Mil/. The cellular band has a bandwidth of 25 MHz and a center frequency of 900 MHz. bach band requires a unique Kb bandpass filter. Therefore, two Kb' processors are used for the two bands. Receiver 1300 comprises many of the same components as those in receiver 1200 (see FIG. 2). Antenna 1312, duplexer 1314, and attenuator 1316 are identical to antenna 1212, duplexer 1214, and attenuator 1216 in receiver 1200. The attenuated signal from attenuator 1316 is provided to l\F processors 13J0a and 1310b. RF processor 1310a is designed to operate at the cellular band and RF processor 1310b is designed to operate at the PCS band. RF processor 1310a is identical to RF processor 1210 in receiver 1200. RF processor 1310a comprises two stages of low-noise amplifier (LNA) 1320a and 1320b connected in cascade with bandpass filter 1326 interposed between the stages. Each LNA 1320 has a parallel signal path comprising pad 1322 and switch 1324. RF processor 1310b is similar to RF processor 1310a except that LNAs 1321a and 1321b and bandpass filter 1327 are designed to operate at the PCS band. The output from RF processors 1310a and 1310b are provided to multiplexer (MUX) 1346 which selects the desired signal in accordance with a control signal from controller 1370 (not shown in FTG. 3 for simplicity). The RF signal from MUX 1346 is provided to RF/IF processor 1348 which is identical to RF/IF processor 1248 in FIG. 2. The IF signal from processor 1348 is provided to demodulator (DEMOD) 1350 which demodulates the signal in accordance with the modulation format used at the remote transmitter (not shown). Demodulator 1350, AGC control circuit 1360, bias control circuit 1380, and non-linearity measurement circuit 1390 in FIG. 3 are identical to demodulator 1250, AGC control circuit 1260, bias control circuit 1280, and non-linearity measurement circuit 1290 in FIG. 2, respectively. Controller 1370 connects to AGC control circuit 1360, bias control circuit 1380, and MUX 1346 and controls the operation of these circuits. Controller 1370 can be implemented as a microprocessor, a microcontroller, or a digital signal processor programmed to perform the functions herein described. Controller 1370 can also comprise a memory storage element for storing the operating modes of receiver 1300 and the associated control signals. Referring to FIG. 2, an exemplary design of receiver 1200 especially adopted for cellular telephone application is given in detail below. In the exemplar}' embodiment, attenuator 1216 has an attenuation range of 20 dB and provides an attenuation of 0.2 dB lo -20 dB. Attenuator 1216 ran be designed with a pair of diodes or by field effect transistors (FRTs), the implementations of which are known in the art. In the exemplary embodiment, l.NAs 1220a and 1220b have fixed gains of 13 dB each. l.NAs 1220a and 1220b can he off-the shelf monolithic RF amplifiers or amplifiers designed using discrete components. An exemplary discrete design of ILA 1220 is given in detail below. In the exemplary embodiment, pads 1222a and 1222b provide 5 dB of attenuation and can be implemented with resistors in the manner known in the art. In the exemplary embodiment, bandpass 4 l * filter 1226 is a suilaee acoustic wave (SAW) filter which has a bandwidth of 25 MHZ., the entire bandwidth of the cellular band, and is centered about 900 MHZ. in the exemplary embodiment; bandpass filter 1232 is also a SAW filter which has a bandwidth of 1.2288 MHz, the bandwidth of one CDMA system, and is centered about 116.5 MHz. Mixer 1230 is an active mixer which can be an off-the-shelf mixer, such as the Motorola MC13143, or other active mixer which is designed in the manner known in the art. Mixer 1230 can also be implemented with passive components, such as double-balanced diode mixer. Amplifier 1234 can be a monolithic amplifier or an amplifier designed with discrete components. In the exemplary embodiment, amplifier 1234 is designed to provide a gain of 40 dB. In the exemplary embodiment, the overall gain range of receiver 1200, excluding demodulator 1250, is 51 dB to -5 dB. This gain range presumes exemplary insertion loss of -3dB for bandpass filter 1226, gain of +1 dB for mixer 1230, and insertion loss of -13 dI3 for bandpass filter 1232. For CDMA applications, an AGC range of 80 dB is typically required to adequately handle path loss, fading conditions; and jammers. In the exemplary embodiment, the AGC range provided by attenuator 1216, LNAs 1220a and 1220b, and pads 1222a and 1222b is 56 dB. In the exemplary embodiment, the remaining 24 dB of AGC range is provided by demodulator 1250 and/or amplifier 1234. Within demodulator 1250 (see FIG. 4), ADC 1410 quantizes the analog waveform and provides the digitized values to the subsequent digital signal processing blocks. In the exemplary embodiment, the required resolution for ADC 1410 is four bits. In the exemplary embodiment an additional six bits of resolution provides headroom for the yet unfiltered jammers. ADC 1410 can be designed to provide more than ten bits of resolution. Kach additional bit over ten can be used to provide 6dB of gain control. Fortunately, at high CDMA signal levels, the out-of-band jammer levels cannot continue to be +72 dB above the CDMA signal. Therefore, when the CDMA signal is strong, the jammers require less than 6 bits of resolution for jammer headroom. In the exemplary embodiment, the AGC function performed in demodulator 1250 is active only when the CDMA signal is strong, e.g., at the high and of the CDMA control range. Thus, the extra hi if. of resolution which are initially reserved for jammer headroom are now used for the AGC function as the result of the strong CDMA signal levels. The design of a subsampiing bandpass ΣA ADC which provides the performance required lor receiver 1200 is disclosed in the aforementioned copending U.S. Patent Application Serial No. . It IL Amplifier Design A schematic diagram of an exemplary discrete LNA design is shown in FlGi. 5A. Within I .MA 1220, the RF input is provided to one end of AC coupling capacitor 1512. The other end of capacitor 1512 connects to one end of capacitor 1514 nod inductor 1516. The other end of capacitor 1514 connects to analog ground and the other end of inductor 1516 connects to one end of resistors 1518 and 1520 and the base of transistor 1540. The other end of resistor 1518 connects to the power supply Vdc and the other end of resistor 1520 connects to analog ground. Bypass capacitor 1522 connects to Vdc and analog ground. In the exemplary embodiment, transistor 1540 is a low noise RF transistor, such as the Siemens BFP420, which is commonly used in the art. The emitter of transistor 1540 connects to one end of inductor 1542. The other end of inductor 1542 connects to current source 1580 which also connects to analog ground. The collector of transistor 1540 connects to one end of inductor 1532, resistor 1534, and capacitor 1536. The other end of inductor 1532 and resistor 1534 connect to Vdc. The other end of capacitor 1536 comprises the RF output. Within LNA 1220, capacitors 1512 and 1536 provide AC coupling of the RF input and output signals, respectively. Capacitor 1514 and inductor 1516 provide noise matching. Inductors 1516 and 1532 also provide matching of the LNA input and output, respectively. Inductor 1532 also provides a DC path for the bias current of transistor 1540. Inductor 1542 provides degeneration of the emitter impedance to improve linearity. Resistors 1518 and 1520 set the DC bios voltage at the base of transistor 1540. Resistor 1534 determines the gain of LNA 1220 and the output impedance. Current source 1580 controls the bias current of transistor 1540 which determines the JIP3 of LNA 1220. A schematic diagram of an exemplary current source 1580 is shown in FIG. 513. The sources of n-chnnnel MOSFETs 1582 and 1584 are connected to analog ground. Tito drain of MOSFET 1584 is connected to one end of resistor 1586. The other end of resistor 1586 connects to the drain of MOSFLT 1582 and comprises the output of current source 1580. Bypass capacitor 1588 connects across the output of current source 1580 and analog ground. The gate of MOSFLT 1582 is connected to Vbiasl and the gate of MOSFF.r 1584 is connected to Vbias2. MOSFETs 1582 and 1584 provide the collector bias current Ice for transistor 1540 which, in turn, determines the IIP3 operating point of LNA 1220. The gates of MOSFETs 1582 and 1584 arc connected to a control voltages Vbiasl and Vbias2, respectively. When Vbiasl is low (e.g. OV), MOSFF.T 1582 is turned OFF and provides no collector bias current Ice for transistor 1540. When Vbiasl is high (e.g. approaching Vdc), MOSFRT 1582 is turned ON and provides the maximum collector bias current for transistor 1540. Thus, Vbiasl determines the amount of collector bias current Ice provided by MOSFF.T 1582. Similarly, Vbias2 determines the amount of collector bias current provided by MOSFFT 1584. However, the voltage at the base of transistor 1540 and the value of resistor 1586 limit the maximum collector bias current provided by MOSFET 1584. The IIP3 performance of LNA 1220 versus collector bias current Ice is illustrated in FIG. bA. Notice that the I1P3 increases approximately 6dB per octave increase (or doubling) in collector bias current. The collector bias current of transistor 1540, the gain of LIMA 1220, and the IIP3 of LNA 1220 versus the control voltage Vbiasl are illustrated in FIG. 6B. Notice that the gain is approximately constant (e.g. gain variation of approximately 1 dB for all Vbiasl voltages). Also, note that the IIP3 varies in similar manner with the collector bias current Ice. Thus, the collector bias current can be decreased, if high HP3 is not required, with minimal effect on the gain of I..NA 1220. FIGS. 5A and 5B illustrate an exemplary design of LNA 1220 and current source 1580, respectively. LNA 1220 can be designed using other topologies to provide the necessary performance (e.g. higher gain, improved noise figure, better matching). LNA 1220 can be designed with other active devices, such as bipolar-junction transistors (BJT), heterojunction-bipolar transistors (FIBT), metal-oxide semiconductor field effect transistor (MOSFET), gallium arsenide field effect transistor (GaAsFET), or other active devices. LNA 1220 can also be implemented as monolithic amplifier in the manner known in the art. Similarly, current source 1580 can be designed and implemented in other manners known in the art. The various implementations of LNA 1220 and current source 1580 are within the scope of the present invention. IIL Variable IIP3 Bias Control As described above, in band intermodulation products can be created by spurious signals passing through non-linear devices. One application which bos a demanding linearity requirement is a CDMA communication system which is co-located with other cellular telephone systems, such as the Ad vain e Mobile Phone System (AMPS). The other cellular telephone systems can transmit spurious signals (or jammers) at high power near the operating band of the CPMA system, thereby necessitating high IIPG requirement on the CDMA receiver. The spurious signal rejection requirement for a CDMA system is defined by two specifications, a two-tone test and a single-tone test, in the "TIA/EIA/lS-98-A Fntcrmodulation Spurious Response Attenuation", hereinafter the IS-98--A standard. The two-tone test is illustrated in FTC 7A. The two tones are located at f2 = +900 KHz and f2 =+1700 KHz from the center frequency of the CDMA waveform. The two tones are equal in amplitude and 58 dB higher than the amplitude of the CDMA signal. This test simulates an FM-modulated signal being transmitted on the adjacent channel, such as the signal from an AMPS system. The FM-modulated signal contains the bulk of the power in the carrier whereas the power in the CDMA waveform is spread across the 1.2288 MHz bandwidth. The CDMA signal is more immune to channel condition and is maintained at a low power level by a power control loop. In fact, the CDMA signal is maintained at the minimal power level necessary for a requisite level of performance to reduce interference and increase capacity. The single-tone test is illustrated in FIG. 713. The single tone is located at fj " >cK)0KHz from the center frequency of the CDMA waveform and has an amplitude of +72 dIJc higher than the amplitude of the CDMA signal. In accordance with IS-98-A, the linearity of the receiver is specified at the CDMA input power level of -101 dBm, -90 dBm, and -79 dBm. For the two-tone test, the jammers are at -43 dBm, -32 dBm, and -21 dBm (t58dBc), and the in-band equivalent signal of the intermodulation products are at -104 dBm, -93 dBm, and -82 dBm, for the input power level of -101 dBm, -90 dBm, and -79 dBm, respectively. As illustrated in FIG. 7A, the spurious tones (or jammers) at f1 = 900 KHz and f2 =+1700 KHz produce third order intermodulation products at (2frf2) -+100 KHz and (2f2-f,) = +2500 KHz. The product at +2500 KHz can be easily filtered by the subsequent bandpass filters 1226 and 1232 (see FIG. 2). However, the product at +100 KHz falls within the CDMA waveform and degrades the CDMA signal. To minimized degradation in the performance of receiver 1200, the IIP3 of the active devices within receiver 1200 is adjusted in accordance with the amount of non-linearity in the received signal. Receiver 1200 is designed to meet the two-tone intermodulation specification. However, in practice, the jammers are present for only a fraction of the operating time of" receiver 1200. Furthermore, the amplitude of the jammers will rarely reach whore P is the power of the baseband signals, and I and Q are the amplitude of the I and Q signals, respectively. The power measurement is provided to • bias control circuit 1280. The power measurement contains the power of the desired baseband I and Q signals as well as the power of the intermodulation products. As described above, for second order non-linearity, the intermodulation products increase two dB for each dB increase in the input signal level. For third order non-linearity, the intermodulation products increase three dB for each dB increase in the input signal level. Thus, the amount of intermodulation can be estimated by measurement of the RSSI slope which is defined as the change in the output signal level versus the change in the input signal level. The change in the input signal level can be set at a predetermined increment (e.g. 05 dB). For receiver 1200 operating in the linear range, 0.5 dB increase in the input signal level corresponds to 0.5 dB increase in the output signal level and an RSSI slope of 1.0. However, as one or more active devices transitions into the non-linear operating region, the RSSI slope increases. A higher RSSI slope corresponds to greater level of non-linearity. An RSSI slope of 3.0 corresponds to receiver 1200 operating in total compression (e.g. no increase in the desired output signal level as the input is increased) and the output heing dominated by third order intermodulation products. In the present invention, the RSSI slope can be compared against a predetermined RSSI threshold. If the RSSI slope exceeds the threshold, the IIP3 of the proper active device is increased. Alternatively, if the RSSI slope is below the RSSI threshold, the IIP3 is decreased. The RSSI threshold can be adjusted during operation of receiver 1200 based on the required bit-error-rate (MFR) or frame-error-rate (I:FR) performance. A higher RSSI threshold allows for higher level of intermodulation products before increasing the IIP3, thereby minimizing power consumption at the expense of BER or FER performance. The RSSI threshold can also be adjusted by a control loop which sets the threshold for a required level of performance (e.g. 1% FER). In the exemplary embodiment, the RSSI slope is selected to be 1.2. However, the use of other RSSI thresholds are within the scope of the present invention. In the present invention, it is not critical to measure the amplitude of the jammers directly. It is more important to measure the undesirable effect of the jammers, in terms of higher level of intermodulation products, on the desired signal. The RSSI slope is one method for measuring the level of non-linearity. The level of non-linearity can also be measured by calculating the change in the energy-per-chip-to-noise-ratio (Ec/Io) of the output signal for an incremental change in the amplitude of the input signal. The intermodulation products increase by a factor of three to one when receiver 1200 is in compression and the output signal is dominated by third order intermodulation products. As with the RSSI slope method, the level of non-linearity can be estimated by the change in Ec/Io versus the change in the input signal level. Other methods to measure the level of non-linearity can be contemplated and are within the scope of the present invention. In the exemplary embodiment, to maximize performance, the IllVJ of the active devices are adjusted in a accordance with the amount of non-linearity (e.g. through measurement of the RSSI slope) experienced by each active device. LNAs 1220a and 1220b provide a fixed gain. Thus, mixer 1230 experiences the largest signal level, LNA 1220b experiences the next largest signal level, and LIMA 1220a experiences the smallest signal level (this RSSI slope is less than the RSSl threshold and the 1IP3 of I.NA 1220b continues to he decreased. At the end of period T4, the measured RSSI slope is still less than the RSSi threshold and the I1P3 of mixer 1230 is decreased since the IIP3 of I.NA 1220b has been adjusted fully to the minimal 1IP3 operating point. At the end of period T5, the measured RSSI slope is greater than the RSSI threshold, indicating that the intermodulation products has increased to an unacceptable level. The IIP3 of mixer 1230 is increased to improve linearity in response thereto. In the exemplary embodiment, each pulse is 200fisec in duration, the period T is 5 msec, and the number of pulses within one period T is nine. Using these values, the duty cycle is 36 percent. In the preferred embodiment, the duty cycle of the pulses should be low enough so that the F.c/lo of the desired signal is minimally degraded by the periodic perturbation in the signal amplitude. The width of the pulses is selected to be short in duration to minimize disturbance to AGC control circuit 1280. Typically, the AGC control loop is slow and cannot track the changes in signal level caused by the short attenuation pulses. This is particularly important since the change in the amplitude of the output signal should accurately reflect the changes in the amplitude of the input signal and the intermodulation products, and not the changes caused by AGC control circuit 1280. However, short pulse width results in less accurate measurement of the output signal power. The present invention is directed at the use of pulses of various widths and various duty cycles for the functions described herein. The amplitude of the perturbation in the input RF signal level is selected to be small to minimize degradation in the output signal and to minimize etfect on the IIP3 of the entire receiver 1200. In the exemplary embodiment, the attenuation step for RSSI slope measurement is 0.5 dB. Other values for the attenuation step can be used and are within the scope of the present invention. In the exemplary embodiment, the RSSI threshold is selected to be 1.2. The use of one RSSI threshold can result in toggling the IIP3 operating points between successive periods T. To prevent this, two RSSI thresholds can br used to provide hysteresis. The IIP3 is not increased unless the measured RSSf slope exceeds the first RSSI threshold and the 11P3 is not decreased unless the measured RSSI slope is below the second RSSI threshold. The use of a single threshold or multiple thresholds are within the scope of the present invention. A diagram illustrating the 11 ['3 bias control operation of receive 1200 of the present invention for ascending input RF power level is shown in FIG. 10A. The input RF signal comprises a CDMA signal and two-tone jammers which are +58 d!5c above the CDMA signal. When the CDMA signal power is between -104 dBm and -101 dBm, the IIP3 of mixer 1230 is set at +10 dBm and the T1P3 of I.NAs 1220a and 1220b are set at 0 dBm. As the CDMA signal increases past 101 dBm, the measured RSSI slope exceeds the RSSI> threshold, and the IIP3 of mixer 1230 is increased to +15 dBm to minimize the level of non-linearity. Attenuator 1216 provides attenuation of the input RF signal between -104 dBm and -84dBm. At -84 dBm, LNA 1220a is bypassed and attenuator 1216 resets to its low attenuation state. When the CDMA signal power is at -83 dBm, -7l> dBm, -75 dBm, and -71 dBm, the IIP3 of LNA 1220b is increased to minimize intermodulation products. At approximately -64 dBm, LNA 1220b is bypassed and attenuator 1216 again resets to its low attenuation state. A diagram illustrating the IIP3 bias control operation of receiver 1200 for descending input RF power level is shown in FIG. 10B. Again, the input RF signal comprises a CDMA signal and two-tone jammers which are +58 el Be above the CDMA signal. Initially, when the CDMA input signal power is at -60 dBm, LNAs 1220a and 1220b are bypassed. When the CDMA signal power decreases to -70 dBm, LNA 1220b is turned ON to provide the necessary gain. At approximately -76 dBm, -80 dBm, -84 dBm, and -88 dBm, the 1IP3 of LNA 1220b is decreased to minimize power consumption. At -90 dBm, attenuator 1216 reaches its upper attenuation range and LNA 1220a is turned ON. At -100 dBm, the IIP3 of mixer 1230 is decreased to conserve power since the input RF signal level is small. As discussed above, the input RF power level where the 1IP3 of mixer 1230 and LNAs 1220a and 1220b are adjusted are determined by the measured RSSI slope. The RSSI slope measurement may not result in linearly spaced 111*3 bias switch points as shown in FIGS. I0A and 10B. Furthermore, the stepwise switch points can be replaced with continuously adjustable bias control. VI. Receiver Setting According to Operating Mode In the second embodiment of the present invention, the I1P3 of the active devices are set in accordance with the operating mode of the receiver. As stated above, receiver 1300 (see FIG. 3) can be used in a cellular telephone which is required to operate in either PCS or cellular band. Each band can * support cither digital and/or analog platforms, Each platform can further comprise n variety of operating modes. The various operating modes are utilized to improve performance and conserve battery power. For example, different operating modes are used to support the following features of a cellular telephone : (1) slotted mode paging for longer stand-by time, (2) gain step for dynamic range enhancement, (3) punctured transmitter output for longer talk time, (1) frequency band selection for dual-band phones (PCS and cellular), (5) multiple access toggling between systems (CDMA, AMPS, GSM, etc.)/ and (6) means for circuit bias control in the presence of jammers. The operating modes of the cellular telephone can have different performance requirements. In the exemplary embodiment, each operating mode is assigned a unique identifier comprising N mode bits. The mode bits define particular characteristics of the operating mode. For example, one . mode bit can be used to select between the PCS and cellular band and another mode bit can be used to select between digital (CDMA) or analog (FM) mode. The N mode bits are provided to a logic circuitry within controller 1370 which decodes the N mode bits into a control bus comprising N up to 2 control bits. The control bus is routed to circuits within receiver 1300 which require control. For example, the control bus can direct the following : (1) set the IIP3 of the mixer within RF/IF processor 1348 and the LNAs within RF processors 1310a and 1310b, (2) set the gain of receiver 1300, (3) set the DC bias voltages and/or current to other RF and IF circuitry within receiver 1300, (4) select the desired signal band, and (5) set the oscillators to the proper frequencies. An exemplary implementation of the 1IP3 control for receiver 1300 based on operating mode is illustrated in Tables 1 and 2. Receiver 1300 supports dual-band (PCS and cellular) and dual-mode (CDMA and FM). In the exemplary embodiment, the PCS band only supports CDMA transmission whereas the cellular band supports both CDMA and FM transmissions (the FM transmission can be from the AMPS system). In the exemplary embodiment, four mode bits are utilized. The four mode bits are the BANDJJELECT, IDLE/, FM/, and LNA_RANGE bits. The BAND„SELECT bit determines the band of operation and is defined as 1=PCS and 0=cellular. The IDLE/ bit (0=idle) sets receiver 1300 into idle mode (e.g. operating at lower 11P3) while the cellular telephone is inactive. The I'M/ bit (0-FM) sets receiver 1300 to process FM signal. And the LNA„ RANGE bit (1-bypass) sets the gain of receiver 1300. When the LNA RANGE bit is set high, designating the bypass mode, Vbiasl and Vbias2 of the first I.N A 1320a or 1321a are set low, ami the LNA is turned OFF. When BAND_SELF.CT is set to 0 (cellular band), receiver 1300 operates in one of the cellular operating modes listed in Table 1. Table 1 only lists the I1P3 operating point of LNAs 1320a and 1320b. A similar table can be generated for the 1IP3 operating point of the active mixer within RF/IP processor 1348. While in the cellular mode, the IX bias current for LNAs 1321a and 1321b are turned OFF to conserve battery power. 1 Tables 1 and 2 list the IIP3 operating points of the LNAs to minimize power consumption while maintaining the require performance. Additional tables can be generated for other circuits which require control. For example, a table can be generated which sets the AGC to the proper operating range based on the expected input signal level for the desired operating mode. Other tables can be generated to set the IX! bias voltages or current which are required by various circuits within receiver 1300. VII. Receiver Setting According to Received Signal Level In the third embodiment of the present invention, the IIP3 of the active devices are set in accordance with the measured amplitude of the signal at various signal processing stages within the receiver. Referring to FIG. 2, power detectors can be connected to the output of selected components to measure the power level of the signal. In the first embodiment o( this receiver setting scheme, power detectors can be connected to the output of LNA 1220a and 1220b and mixer 1230 to measure the power of the RI; signal from these components. The power measurements are then provided to bias control circuit 1280 which use the information to adjust the UP3 operating point of any component operating past a predetermined level of non-linearity. In the second embodiment of this receiver setting scheme, power detectors can be connected to the output of mixer 1230 and demodulator 12S0 to measure the power of the RF signal and baseband signal, respectively, from these components. The power measurements are also provided to bias control circuit 1280. The difference in power between these two measurements represents the power from flu* out-of-band signals, which can be used to infer the required IIP! performance. Bias control circuit 1280 adjusts the operating point of the components in the manner described above to maintain the required level of performance. The power detector can be implemented in many manner known in the art, such was a diode detector follow by a lowpass filter. * VIII. ZA ADC Setting According to Required Dynamic Range As disclosed in copending U.S. Application Serial No. _ , the HA ADC within the receiver of the present invention can be designed to provide the required dynamic range while minimizing power consumption. Power consumption is especially important in CDMA communication systems because of the portable nature of the cellular telephone. The IA ADC can be designed to minimize power consumption by providing for sections of the LA ADC to be disabled when high dynamic range is not required. The EA ADC can also be designed with adjustable bias current which can be varied based on the amplitude of the signal into the XA ADC and the required performance. The reference voltage of the EA ADC can also be adjusted lower when less dynamic range is required to minimize power consumption. Finally, the sampling frequency of the XA ADC can also be lowered when high dynamic range is not required to further minimize power consumption. The features described above can be combined, as appropriate, to provide the required level of performance while maximizing power savings. In the exemplary CDMA communication system, the receiver is designed to operate under various operating conditions as specified by the IS-98-A standard. In the exemplary embodiment, the input RF signal comprises a CDMA signal which ranges from -104 dl3m to -79 clBm. In addition, IS-98-A specifies a two-tone and a single-tone operating condition. For the two-tone operating condition, the input RF signal comprises the CDMA signal and two jammers which are each +58 dBc above the amplitude of the CDMA signal and are located +900KHz and I 1700KH/ from the center frequency of the CDMA signal. For the single-tone operating condition, the input RF signal comprises the CDMA signal and a signal jammer which is +72 dBc above the amplitude of the CDMA signal and is located +900KI 1/ from the center frequency of the CDMA signal. performed on the desired signal alter the digital signal processing whirh removes undesirable images ami spurious signals. The amplitude of the signal into the XA ADC can be measured by a power detector connected to the input of the JLA ADC. The power detector can be implemented in the manner known in the art, such as an envelop detector implemented with a diode1 or a peak detector. The peak detector can detect if the input signal into the IA ADC is above the saturating voltage of the IA ADC which is half of the reference voltage. When this occurs, the IA ADC can be switched to a higher dynamic range mode. Alternatively, the amplitude of the signal into XA ADC can be estimated from measurement of the amplitude of the signal from various components within the front end, such as the output of mixer 1230 or the output of bandpass filter 1234 (see FIG. 2). Again, a power detector can be used to measure the amplitude of the signal. The gain of the components interposed between the power detector and the EA ADC is taken into account in calculating the amplitude of the signal into the IA ADC. Furthermore, the spectral content of the measured signal should approximate the spectral content of the signal into the SA ADC to enhance the accuracy of the estimate. Inaccuracy in the estimate results in a non-optimal dynamic range adjustment mechanism. Based on the measured amplitude of the desired signal and the signal into the LA ADC, the required dynamic range can be computed as : where DKrpquircd is tlu" required dynamic range in dB, VAIx: is the amplitude of the signal into the LA ADC, and Visited is *e amplitude of the desired signal at the input of the IA ADC. Alternatively, the required dynamic range can be determined based on the operating mode of the receiver. Each operating mode can be associated with a different operating condition. For example, CDMA mode require* high dynamic range because of possible jammers near the signal band. I;M mode requires less dynamic range since the input requirements are less stringent. In the exemplary embodiment, 12 bits of resolution are provided by a two-loop MASH 4-t architecture as disclosed in copending U.S. Patent Application No. . . Referring to FIG. 11, loop 110a provides a first dynamic range and has a low noise floor. Loop 110b provides a second dynamic range but has a slightly higher noise floor than loop 110a. Ihe lower noise floor of loop 110a is partially the result of biasing the amplifiers within loop 110a with higher bias current and using larger capacitors with loop 110a. In the exemplary embodiment, each loop 110 within MASH ADC 100 can be selectively disabled, based on the amplitude of the signal into the LA ADC and the required dynamic range, to minimize power consumption. In addition, the bias current of the amplifiers within each loop 110 can he adjusted to minimize power consumption and maintain the required performance. When high dynamic range is required, the signal into the ZA ADC is provided to loop 110a, the bias current of all amplifiers is set high, and MASH ADC 100 operates in the manner described above. This operating condition may result from an input RF signal comprising the CDMA signal and two large jammers at +58dbc or an input RF signal comprising the CDMA signal and one large jammer at +72dBc. As the amplitude of the desired signal increases or the amplitude of the jammers decreases, less dynamic range is required. When this occurs, loop 110b can be disabled and the output Yl from loop 110a comprises the output from the ZA ADC. Alternatively, loop 110a can be disabled, the signal into the ZA ADC can be provided to loop 110b, and the output Y2 from loop 110b comprises the output from the LA ADC. Thus, one to two loops can be enabled to provide the required dynamic range. The dynamic range thresholds wherein the loops are disabled can be selected based on numerous considerations. The thresholds can be selected based on the statistics of the amplitude of the input RF signal. For example, the percentage of time the input RF signal comprises jammers of various amplitudes can be tabulated. This information can be used to select the dynamic range thresholds which yield the minimum power consumption by ensuring that the minimal number of loop is enabled most of the time. The thresholds can also be selected based on the design performance of the ZA ADC. For example, if a first loop design which provides for X dB of dynamic range requires substantially more power than a second loop design which provides for Y dB of dynamic range, where Y is only slightly less than X, the second design may he preferred and the dynamic range threshold can be selected in accordance with the performance of the second loop design. Numerous other considerations can be contemplated when selecting the dynamic range thresholds and are within the scope of the present invention. Furthermore, each threshold can be implemented with hysteresis to prevent toggling of Ihe loops between the enabled and disabled states. An exemplary implementation of hysteresis is described below. The bias current of the amplifiers in each loop 110 can be adjusted to minimize power consumption while providing the required performance. In the exemplary embodiment, loop 110a is designed to consume a maximum of 10 mA of bias current and loop 110b is designed to consume a maximum of 6 mA of bias current. In the exemplary embodiment, within loop 110a, the amplifier within resonator 130a is designed to consume 6 mA and the amplifier within resonator 130b is designed to consume 4 mA. When high dynamic range is required, the bias current for each amplifier is set high. When high dynamic range is not required, the bias current can be decreased. Dynamic range varies approximately proportional to the bias current such that a two-fold decrease in bias current results in 6 dB less of dynamic range. Thus, the bias current of the amplifier within resonator 130a can be decreased from 6 mA down to 3 mA and the bias current of the amplifier within resonator 130b can he decreased from 4 mA down to 2 mA when 6 dB less of dynamic range is required. Similarly, the bias current for the amplifiers within loop 110b can be decreased accordingly when high dynamic range is not required. In the present invention, the bias current can be adjusted in discrete steps or in a continuous manner. An additional mechanism to minimize power consumption is through adjustment of the reference voltage within the ZA ADC. The dynamic range of the ZA ADC is determined by the maximum input signal swing and the noise from ZA ADC which comprises the circuit noise and the quantization noise. As the required dynamic range decreases, the reference voltage can be lowered while maintaining approximately the same noise level. This is especially true when one loop is switched out and the quantization noise increases such that it is much greater than the circuit noise because the reference voltage of the ZA ADC is maintained constant. By lowering the reference voltage such that the quantization noise is approximately equal to the circuit noise, the desired level of performance is provided while maintaining the signal level at a low level. By decreasing the reference voltage and the signal swing within the ZA ADC, the amplifier bias current can be decreased. As an additional benefit, the amplifier driving the ZA ADC has a lower maximum signal swing and can also be biased with less current. Adjustment of the amplifier bias current can be performed independently of the disablement of the loops, or can be performed in conjunction with the disablement of the loops. In the exemplary embodiment, the loops are enabled based on a coarse range of required dynamic range and the bias current are used for fine adjustment of dynamic range. Alternatively, analysis and measurements can be performed to determine the dynamic range provided by various configurations of the SA ADC. Ibis information can be tabulated and stored. Then, based on the required dynamic range, the LA ADC can be configured accordingly, using the tabulated data. The various methods used to configure the ZA ADC to provide the required dynamic range while minimizing power consumption are within the scope of the present invention. In the exemplary embodiment, the ZA ADC provides 79 dB of dynamic range (or greater than 12 bits of resolution) when both loops are enabled and an oversampling ratio (OSR) of 32 is utilized. For bandpass XA ADC, the oversampling ratio is defined as the sampling frequency over two OSR = -£ (imes the two-sided bandwidth of the input signal, or The equivalent number of bits can be calculated from the dynamic range, and vice versa, according to the equation : where M is the number of bits and DR is in dB. In the exemplary embodiment, loop 110a provides 54 dB of dynamic range, loop 110b provides 42 dB of dynamic range, and loops 110a and 110b provide 79 dB of dynamic range when combined. In the exemplary embodiment, when the required dynamic range is less than 36 dB loop 110b is utilized, when the required dynamic range is between 36 dB and 48 dB loop 110a is utilized, and when the required dynamic range is greater than 48 dB loops 110a and 110b are utilized. In the exemplary embodiment, a margin of 6 dB is reserved to handle fluctuations in the amplitude of the input RF signal. The dynamic range thresholds can be implemented with hysteresis to prevent toggling between the enabled and disabled states. For the exemplary embodiment described above, each dynamic range threshold comprises an Upper threshold and a lower threshold. The loop with the higher dynamic range is not enabled unless the required dynamic range exceeds the upper threshold and the loop with the lower dynamic range is not enabled unless the required dynamic range falls below the lower threshold. For example, with 6 dB of hysteresis, loop 110a is not enabled unless the required dynamic range exceeds 51 dB. While operating with only loop 110a, loop 110b is We Claims: CLAIMS J. A programmable dynamic range receiver comprising : a front end for receiving an RF signal and producing an IF signal; a EA ADC connected to said RF processor for receiving said IF signal and producing IF samples, said ΣA ADC having a dynamic range; a power detector connected to said RF processor for measuring an amplitude of said IF signal; and a digital signal processor connected to said ΣA ADC for receiving said IF samples and producing a desired signal; wherein said dynamic range of said ΣA ADC is adjusted based on a required dynamic range, said required dynamic range dependent on said amplitude of said IF signal. 2. The receiver of claim i wherein said ΣA ADC comprises multiple loops, each loop being enabled or disabled depending on said required dynamic range. 3. The receiver of claim 2 wherein said ΣA ADC is a MASH 4-4 ADC, said MASH 4-4 ADC comprising a first loop and a second loop. 4. The receiver of claim 3 wherein said first loop of MASH 4-4 ADC is utilized when the required dynamic range is less than a first dynamic range threshold, said second loop is utilized when the required dynamic range is above said first dynamic range threshold and less than a second dynamic range threshold, and said first loop and said second loop are utilized when the required dynamic range is above said second dynamic range threshold. 5. The receiver of claim 4 wherein said first and second dynamic ! range thresholds are implemented with hysteresis. 6. The receiver of claim 1 wherein said ΣA ADC comprises amplifiers, said amplitiers having bias current. 7. The receiver of claim 6 wherein said bias current of said amplifiers is adjusted based on said required dynamic range. 8. A method for providing programmable dynamic range in a receiver comprising the steps of: receiving an RF signal; processing said RF signal to produce an IF signal; sampling said IF signal with a IA ADC to produce IF samples, said ΣA ADC having a dynamic range; processing said IF samples to produce a desired signal; measuring an amplitude of said IF signal; measuring an amplitude of said desired signal; computing a required dynamic range in accordance with said measured amplitude of said IF signal and said measured amplitude of said desired signal; and adjusting said dynamic range of said ΣA ADC in accordance with said required dynamic range. 9. The method of claim 8 wherein said adjustment step comprises the step of: enabling a first loop within said ΣA ADC when said required dynamic range is below a first dynamic range threshold. 10. The method of claim 9 wherein said adjustment step further comprises the step of : enabling a second loop within said ΣA ADC when said required dynamic range is above said first dynamic range threshold and below a second dynamic range threshold. 11. The method of claim 10 wherein said adjustment step further comprises the step of: enabling said first loop and said second loop within said ZA ADC when said required dynamic range is above said second dynamic range threshold. 12. The method of claim 11 wherein said first and said second dynamic range thresholds are implemented with hysteresis. 13. The method of claim 11 wherein said first and said second dynamic range thresholds are selected based on statistics of said RF signal. 14. The method of claim 11 wherein said first and said second dynamic range thresholds are selected based on performance of said ΣA ADC. 15. The method of claim 8 wherein said adjustment step comprises the step of: adjusting a bias current of said ΣA ADC based on said required dynamic range. 16. The method of claim 8 wherein said adjustment step comprises the step of: change a sampling frequency of said EA ADC based on said required dynamic range. 17. The method of claim 16 wherein said adjustment step further comprises the step of: maintaining an oversampling ratio of said EA ADC at a minimum of 16. 18. The method of claim 8 wherein said RF signal comprises a CDMA signal. 19. The method of claim 18 wherein said IA ADC has more than four bits of resolution. 20. The method of claim 19 further comprising the step of: maintaining said desired signal at 18 dB above a noise floor of said EA ADC. 21. The method of claim 20 wherein said required dynamic range is computed such that said IF signal is not clipped by said IA ADC. 22. The method of claim 1 wherein said required dynamic range is further dependent on said amplitude of said desired signal. 23. A programmable dynamic range receiver, substantially as herein described, with reference to the accompanying drawings. 24. A method for providing programmable dynamic range in a receiver, substantially as herein described, with reference to the accompanying drawings.

Documents:

2747-mas-1998-abstract.pdf

2747-mas-1998-assignment.pdf

2747-mas-1998-claims duplicate.pdf

2747-mas-1998-claims original.pdf

2747-mas-1998-correspondence others.pdf

2747-mas-1998-correspondence po.pdf

2747-mas-1998-description complete duplicate.pdf

2747-mas-1998-description complete original.pdf

2747-mas-1998-drawings.pdf

2747-mas-1998-form 1.pdf

2747-mas-1998-form 19.pdf

2747-mas-1998-form 26.pdf

2747-mas-1998-form 3.pdf