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Current reduction by dynamic receiver adjustment in a communication deviceRelated Patent Categories: Telecommunications, Transmitter And Receiver At Separate Stations, Having Measuring, Testing, Or Monitoring Of System Or Part, Noise, Distortion, Or Unwanted Signal Detection (e.g., Quality Control, Etc.)Current reduction by dynamic receiver adjustment in a communication device description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060040617, Current reduction by dynamic receiver adjustment in a communication device. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a divisional of pending U.S. application Ser. No. 10/630,124 filed Jul. 30, 2003, and assigned to Motorola, Inc., from which priority is hereby claimed under 35 U.S.C. .sctn. 120. FIELD OF THE INVENTION [0002] The present invention generally relates to reducing power consumption in a communication device such as a radiotelephone. More particularly, the present invention relates to a technique for dynamic adjustment of receiver elements in radiotelephone device. BACKGROUND OF THE INVENTION [0003] Code Division Multiple Access (CDMA) and Wideband CDMA (WCDMA) receivers in North American bands have been and will continue to coexist with other narrow band systems such as AMPS, IS136, and Global System for Mobile (GSM) communication system. This situation leads to narrow band interference signals that cause both crossmodulation and intermodulation non-linear distortions. The traditional method to mitigate the distortion is to operate with sufficiently high linearity at the expense of additional current drain. Additionally, receiver designs are migrating to higher dynamic range analog-to-digital converters (A/Ds) with digital filters and less analog filtering. This type of receiver design therefore passes both the desired signal and interference through a set of high dynamic range circuit elements before final elimination of the interference by digital filters. Again, the dynamic range of these circuit elements (A/Ds and filters) is set sufficiently high to accommodate the largest expected interference at the expense of current drain and battery life. These two factors cause receivers to operate with higher current drain than needed under the majority of usage conditions. [0004] Interference is a particular problem in CDMA systems which require the receiver and transmitter to be on continuously. An example of such a specification is Telecommunications Industry Association/Electronic Industry Association (TIA/EIA) Interim Standard IS-95, "Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System" (IS-95). IS-95 defines a direct sequence code division multiple access (DS-CDMA or CDMA) radiotelephone system. In a CDMA system, the receiver must be on continuously in order to receive incoming data while on a traffic channel and the transmitter must be on continuously while on a traffic channel. [0005] Prior art receiver linearity systems dynamically adjust the linearity of a receiver based on detection of poor received signal quality based on carrier-to-interference ratio (Ec/Io) or FER (frame error rate), knowledge of the transmit level, and received signal strength indications (RSSI). Also, the prior art captures the various ways that linearity can be changed, i.e. either gain change or current change in receiver amplification stages. However, the prior art does not make the most efficient use of current drain since the linearity is potentially increased without any knowledge of the interference. Poor quality can be caused by a number of factors that are not related to receiver linearity and thus is not the most efficient metric. Furthermore, the prior art does not address the use of variable dynamic range in the baseband. [0006] In another technique, the quality metric shortcoming is somewhat addressed by performing a spectral estimation of the in-band signal. This spectral estimation is performed in post-channel filtering to look for narrowband intermodulation distortion products and a low-noise amplifier (LNA) bypass is used to improve receiver linearity. Note that this addresses potential intermodulation products but does not consider crossmodulation. Also, the mitigation is limited to LNA bypass and thus limits the optimization of performance near sensitivity. Furthermore, detection of the intermodulation products is much more difficult than detection of the interference since the intermodulation products are several dB lower in amplitude than the actual interference. [0007] Dynamic control of A/D converter dynamic range is also known, wherein an analog detected voltage is used to vary an A/D's dynamic range. The variable control of converter range is often internal to the A/D and is not part of a larger system. This limits the efficacy of the techniques to mitigation of narrow-band interferer by the A/D and does not provide a mechanism to reduce the current drain of the other circuit elements, e.g. digital filters, analog filters, and RF circuits. [0008] Accordingly, there is a need for a method and apparatus for reducing current drain in a communication device such as a radiotelephone when mitigating non-linear distortion effects. There is a further need to reduce the current drain by the receiver in a communication device operating in a CDMA system, without sacrificing the ability to receive incoming signals. It would also be of benefit to provide these advantages without additional hardware, which would increase the cost of the communication device. BRIEF DESCRIPTION OF THE DRAWINGS [0009] The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by making reference to the following description, taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify identical elements, and wherein: [0010] FIG. 1 shows a block diagram of a prior art multimode communication device; [0011] FIG. 2 is a flow chart illustrating the operation of the device of FIG. 1; [0012] FIG. 3 shows a block diagram of a first embodiment of a multimode communication device, in accordance with the present invention; [0013] FIG. 4 is a flow chart illustrating the operation of the device of FIG. 3; [0014] FIG. 5 shows a block diagram of an alternate embodiment of a multimode communication device, in accordance with the present invention; [0015] FIG. 6 is a flow chart illustrating the operation of the device of FIG. 5; and. [0016] FIG. 7 is a flow chart for a method of reducing current drain in a receiver, in accordance with the present invention. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT [0017] The present invention provides a unique method to improve reception in a receiver circuit for a wireless communications device in a communication system while reducing current drain. This is done by reducing the current drain in the receiver by making the elements in the receiver (mixers, amplifiers and filters) less linear when there is little or no interference, and increasing linearity again when interference exists. In particular, the present invention reduces the effects of intermodulation distortion and crossmodulation distortion by direct determination of the interference, instead of relying on channel quality, and by improving linearity of the receiver only when non-linear distortion products are anticipated. This improvement is accomplished without any significant additional hardware or cost in the communication device. Moreover, the present invention can take advantage of existing high dynamic range devices such as analog-to-digital converters and digital filters in combination with solutions for processing of the RF input signals necessary in the communication device. [0018] Specifically, the present invention resolves the problems of the prior art by using in-band and out-of-band interference detection and spectrum estimation to identify the power level and frequency offsets of interference to decide if linearity reduction is performed, rather than using a CDMA channel quality metric or for use in a GSM environment (e.g. for cross modulation or intermodulation issues). Further, the present invention can also utilize dynamic range reduction to the same effect and linearity adjustments, wherein dynamic range adjustments and linearity adjustments can be used separately or in combination. [0019] Turning to FIG. 1, a block diagram of a prior art communication device is shown. Typically, this device is a duplex CDMA cellular radiotelephone operable in a CDMA radiotelephone system operating according to TIA/EIA Interim Standard IS-95, "Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System," operating at 800 MHz. Alternatively, the radiotelephone system 100 could operate in accordance with other CDMA systems including PCS systems at 1800 MHz or with any other suitable digital radiotelephone systems. The device includes an antenna 106 coupled to a transmitter 100 and a receiver circuit 102, which can communicate simultaneously, although in different frequency bands, through a duplexer filter 104 with an antenna 106. The device is controlled by one or more of a microprocessor (not shown), microcontroller, or digital signal processor 108 (DSP), which generate the necessary communication protocol for operating in a compatible cellular system and can perform many other devices that provide functions for the wireless communication device, such as writing to a display, accepting information from a keypad, communicating through a user interface, audio, etc. These other devices are not shown for simplicity of the figures and to avoid confusion. A battery 105 provides operating power to the other components of the radiotelephone. Preferably, the battery is rechargeable. Continue reading about Current reduction by dynamic receiver adjustment in a communication device... 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