Patent Publication Number: US-2007098118-A1

Title: Method for automatic gain control (AGC) by combining if frequency adjustment with receive path gain adjustment

Description:
BACKGROUND  
      The present disclosure relates generally to the field of data communications, and more particularly to an improved system and method for performing automatic gain control (AGC) in a communication device.  
      The basic operation of a communication system is well known in the art. The communication system typically includes a transmitter and a receiver operating cooperatively to convey data and/or information from an operator of the transmitter to a user of the receiver via a communications media. The media may be wired and/or wireless.  
      Multiple technological standards may be adopted for use in wireless media applications. For example, IEEE 802.11, Bluetooth, Global System for Mobile Communications (GSM), and Infrared Data Association (IrDA) are widely accepted standards for wireless communications. Regardless of the standard used, wireless devices typically operate in certain predefined frequency spectra.  
      A receiver typically includes a downconverter component and a demodulator component. In the downconverter, the received signal having a predefined carrier frequency is received and converted to a lower intermediate frequency (IF) signal that may be more suitable for the demodulator. The IF signal is then typically: 1) filtered to select the signal of interest and reject unwanted signals, 2) amplified by a baseband amplifier, and 3) digitized by an analog-to-digital converter (ADC). The demodulation, which may include complex demodulation algorithms, is typically performed in the digital domain by a digital signal processor (DSP).  
      Two well known topologies for receiver circuits include the heterodyne and the homodyne receiver. Heterodyne receivers typically include a downconversion to an IF signal, whereas homodyne receivers typically do not include an IF signal. Thus, heterodyne and homodyne receivers are often referred to as IF and zero-IF receivers, respectively. Homodyne receiver circuits are typically more compact and hence may be better suited to be implemented as an integrated circuit (IC) chip compared to a traditional heterodyne receiver circuit, which typically includes bulky components. Although full integration is desirable for cost reduction, the use of homodyne receivers have been limited in the past due to the poor performance compared to traditional heterodyne receivers. More recently, a low IF receiver circuit, which combines a high level of integration with a higher performance, is increasingly being used in communication systems.  
      Some of the traditional heterodyne, homodyne and low IF topology based receivers are described in further detail in the following technical papers and U.S. patents, which are hereby incorporated herein by reference into this specification: 1) ‘A Discrete Time Quad-band GSM/GPRS Receiver in a 90 nm Digital CMOS Process’, K. Muhammad, Y.-C. Ho, T. Mayhugh, C.-M. Hung, T. Jung, I. Elahi, C. Lin, I. Deng, C. Fernando, J. Wallberg, S. Vemulapalli, S. Larson, T. Murphy, D. Leipold, P. Cruise, J. Jaehnig, M.-C. Lee, R. B. Staszewski, R. Staszewski and K. Maggio, IEEE Custom Integrated Circuits Conference, Sep. 18-21, 2005, San Jose, Calif., 2) ‘Low-IF Topologies for High-Performance Analog Front Ends of Fully Integrated Receivers’, Jan Crols and Michiel S. J. Steyaert, IEEE Transactions On Circuits And Systems-II: Analog And Digital Signal Processing, Vol. 45, No. 3, March 1998, and 3) U.S. Pat. No. 6,882,208, Suissa et al., entitled ‘Adjustment Of Amplitude And DC Offsets In A Digital Receiver’.  
      However, current AGC techniques typically adjust only the gain of the receive path, e.g., path of the received signal, in order to extend the dynamic range of the receiver and avoid receiver saturation. This imposes stricter margins on the receiver gain path when considering process and temperature variations.  
      Therefore, a need exists to provide an improved method and system for performing AGC in a communications device. Specifically, there is a need for an improved AGC control device in a receiver that provides improved integration, higher performance, and improved filtering of unwanted signals without saturating the receiver. Accordingly, it would be desirable to provide an efficient method and system for performing AGC to eliminate the disadvantages found in the prior techniques discussed above.  
     SUMMARY  
      The foregoing need is addressed by the teachings of the present disclosure, which relates to an improved method and system for adjusting gain controls of a receiver. According to one embodiment, in a method and system for performing automatic gain control (AGC) in a receiver, an automatic integrated controller (AICTR) device includes a gain controller (GC) to control an amplitude of an input signal provided to the receiver, with the interfering signal and the signal of interest being included in the input signal. The GC maintains the amplitude within a predefined range to operate the receiver substantially close to saturation. The AICTR device also includes a frequency controller (FC) to control a frequency of a local oscillator (LO) signal. The LO signal is mixed with the input signal to generate an intermediate frequency (IF) signal. The FC changes the frequency of the LO signal to increase or decrease a frequency of the IF signal. A greater attenuation is provided to the interfering signal compared to an attenuation for the signal of interest by the reduction in frequency of the IF signal.  
      In one aspect of the disclosure, a method for performing automatic gain control (AGC) in a receiver includes adjusting a gain of an input signal received by the receiver to operate the receiver substantially close to saturation. The input signal includes an interfering signal and a signal of interest. An intermediate frequency (IF) of the receiver is reduced to provide greater attenuation to the interfering signal compared to an attenuation for the signal of interest.  
      Several advantages are achieved by the method and system for controlling gain of a receiver according to the illustrative embodiments presented herein. The embodiments advantageously provide for more robust margins on the receiver path gain when considering process and temperature variations. In addition, the embodiments advantageously provide the benefit of reducing the level of the largest interferers while decreasing the noise figure of the receiver, thereby allowing a potential decrease in the receiver gain without increasing the original noise figure of the receiver.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  illustrates a block diagram of a receiver, according to an embodiment;  
       FIG. 2  is a graphical diagram illustrating amplitude versus frequency response characteristics of a receiver, according to an embodiment;  
       FIG. 3  is a block diagram of an integrated receiver, according to an embodiment; and  
       FIG. 4  is a flow chart illustrating a method for performing automatic gain control (AGC) in a receiver, according to an embodiment.  
    
    
     DETAILED DESCRIPTION  
      Novel features believed characteristic of the present disclosure are set forth in the appended claims. The disclosure itself, however, as well as a preferred mode of use, various objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings. The functionality of various circuits, devices or components described herein may be implemented as hardware (including discrete components, analog, digital and/or mixed circuits, integrated circuits and systems-on-a-chip ‘SoC’), firmware (including application specific integrated circuits and programmable chips) and/or software or a combination thereof, depending on the application requirements.  
      The following is a glossary of terms used in this disclosure:  
                                                   Term   Description                          ABE   Analog Back End           A/D   Analog to Digital           ADC   Analog/Digital Converter           AFE   Analog Front End           AGC   Automatic Gain Control           AICTR   Automatic Integrated Controller           BER   Bit Error Rate           BPF   Band Pass Filter           BTS   Base Transceiver Stations           CDMA   Code-division Multiple Access           CTA   Continuous Time Amplifier           dBm   decibel milliwatts           DC   Direct Current           DRX   Digital Receiver           DSP   Digital Signal Processor           FC   Frequency Controller           GC   Gain Controller           GPS   Global Positioning System           GSM   Global System for Mobile Communications           HB   High Band           IC   Integrated Circuit           IF   Intermediate Frequency           I/Q   I channel and Q channel           LB   Low Band           LNA   Low Noise Amplifier           LPF   Low Pass Filter           LPFC   Low Pass Filter Controller           LO   Local Oscillator           MHz   Megahertz           MTDSM   Multi-Tap Direct-Sampling Mixer           OCP   Open Core Protocol           QOS   Quality of Service           RF   Radio Frequency           RSSI   Receive Signal Strength Indicator           SDADC   Sigma Delta Analog/Digital Converter           SDC   Sigma Delta Converter           SoC   Systems-on-a-chip           TA   Transconductance Amplifier           TA/MIX   Transconductance Amplifier/Mixer           TDMA   Time-division Multiple Access           VGA   Variable Gain Amplifier                      
 
      Traditional automatic gain control (AGC) mechanism typically adjusts only the gain of the receive path in order to extend the dynamic range of the receiver. For low power signals (e.g., at sensitivity) it provides maximum gain in the receiver. As the input signal of interest increases in amplitude/energy, it reduces the receiver gain so that an adjacent blocker does not saturate the receive path. Generally, only the receiver gain is adjusted to prevent receiver saturation, which imposes stricter margins of the gain when considering process and temperature variations. These problems may be addressed by an improved system and method for controlling gain of a receiver. In an improved method and system for performing automatic gain control (AGC) in a receiver, an intermediate frequency (IF) of the receiver is reduced to provide greater attenuation to the interfering signal compared to an attenuation for the signal of interest.  
      According to one embodiment, in a method and system for performing automatic gain control (AGC) in a receiver, an automatic integrated controller (AICTR) device includes a gain controller (GC) to control an amplitude of an input signal provided to the receiver, with the interfering signal and the signal of interest being included in the input signal. The GC maintains the amplitude within a predefined range to operate the receiver substantially close to saturation. The AICTR device also includes a frequency controller (FC) to control a frequency of a local oscillator (LO) signal. The LO signal is mixed with the input signal to generate an intermediate frequency (IF) signal. The FC changes the frequency of the LO signal to increase or decrease a frequency of the IF signal. A greater attenuation is provided to the interfering signal compared to an attenuation for the signal of interest by the reduction in frequency of the IF signal.  
      As described earlier, regardless of the standard used, wireless devices such as radio frequency (RF) transceivers (e.g., receiver and transmitter combined in one device) typically operate in certain predefined frequency spectra. For example, a mobile phone that is compliant with the GSM 900 technical standard uses a radio transceiver operating in a 900 megahertz (MHz) radio frequency band and a quad band cellular phone that is compliant with the GSM850, EGSM900, DCS1800 and PCS1900 standard may include a transceiver operable to receive RF signals in the 800 to 1000 MHz and 1800 to 2000 MHz range. The receiver and/or transmitter may be included as a part of another circuit or device such as a microprocessor, a digital signal processor, a radio frequency integrated circuit, and/or a microcontroller.  
      The standards also typically define power levels for transmit and receive signals to maintain desired signal strength, minimum signal-to-noise ratio (SNR) for the receiver, and/or quality of service (QOS). The QOS may be defined by a maximum allowable bit error rate (BER) for the RF signal. For example, according to the Bluetooth standard in a modulated RF input signal at −70 decibel milliwatts (dBm) power level, the data output of the receiver may not have a bit error rate (BER) exceeding 10 −3 . The GSM standard defines five classes of mobile stations according to their peak transmitter power, e.g., 20, 8, 5, 2, and 0.8 watts. To minimize co-channel interference and to conserve power, both the mobiles and the Base Transceiver Stations (BTS) operate at the lowest possible power level while maintaining an acceptable signal strength and QOS. Power levels may be stepped up or down by adjusting receiver gain and hence an amplitude of the signal in steps of 2 dB from the peak power for the class down to a minimum of 13 dBm (20 milliwatts).  
       FIG. 1  illustrates a block diagram of a receiver  100 , according to an embodiment. The receiver  100  includes techniques for adjusting intermediate frequency (IF) f IF  and gain to improve receiver performance without saturating the receiver. Although the receiver  100  is described using analog function blocks, it is understood that the receiver  100  may be implemented using various alternative technologies such as analog signal processing, digital domain signal processing, mixed signal processing and/or a combination thereof. For example, a filter block may be implemented in an analog form using continuous-time or discrete-time RF signals or as a digital filter using binary signals. Additional details of a digital receiver architecture for adjusting intermediate frequency (IF) f IF  and gain to improve receiver performance without saturating the receiver is described with reference to  FIG. 3 .  
      In the depicted embodiment, a low noise amplifier (LNA)  110  receives an input signal  102 . The input signal  102 , which may include one or more RF bands, includes a signal of interest at a carrier frequency f c  and one or more interfering or unwanted signals.  
      In a non-depicted, exemplary embodiment, the input signal  102  may be received from an antenna coupled to the receiver  100  and filtered by a front end band pass filter (BPF) to remove high frequency signals. The BPF serves to protect the receiver  100  from saturation by interfering signals at the antenna. Receiver saturation may be described as a condition or an operating state of the receiver  100  in which a further increase in one variable such as gain produces no further increase in the resultant effect such as the output signal. Receiver saturation generally occurs at higher power levels of interfering signals compared to the desired signal. In the depicted embodiment, the LNA  110  provides an amplified input  112  in response to the input signal  102 . In a particular embodiment, a gain of the LNA  110  is controlled by a LNA control signal  114 .  
      A local oscillator (LO)  120  provides a LO signal  122  having a variable frequency. The variable frequency of the LO signal  122  is controlled by a LO control signal  124 . A mixer  130  is operable to downconvert the signal of interest from its carrier frequency f c  to a lower intermediate frequency (IF) having the frequency f IF . The down-conversion process may utilize a difference between the mixer  130  RF input (the amplified input  112 ) and local oscillator input (LO) (LO signal  122 ) where for a low side injection the LO signal  122  is less than the RF signal (the IF frequency f IF  is positive) and for a high side injection the LO signal  122  is greater than RF signal (IF frequency f IF  is negative). That is, the mixer  130  mixes the signal of interest received as the amplified input  112  and the LO signal  122  to provide an intermediate frequency (IF) signal  132  having the frequency f IF . In a non-depicted, exemplary embodiment, the IF signal  132  includes the signal of interest at a frequency f c  and an interfering signal. The frequency f IF  may be adjusted to any value ranging from +f IF  to −f IF , including 0. Although a single IF downconversion stage is shown, it is understood that multiple downconversion stage IF&#39;s may be deployed in receivers.  
      In the depicted embodiment, a low pass filter (LPF)  140  centered around the IF frequency receives the IF signal  132  and provides a filtered IF signal  142  after filtering out at least one of the interfering signal. In a particular embodiment, the LPF  140  is a real low pass filter such as a Butterworth filter. The LPF  140  has predefined filter response characteristics such as corner frequency, slope and bandwidth. The response characteristics of the LPF  140  are controlled by a LPF control signal  144 . Additional details of the response of the signal of interest and the interfering signal to a reduction in IF is described with reference to  FIG. 2 .  
      In the depicted embodiment, a variable gain amplifier (VGA)  150  receives the filtered IF signal  142  and provides an amplified filtered IF signal  152  having an amplitude/energy within a predefined range. A gain factor of the VGA  150  is controlled by a VGA control signal  154 . The amplitude/energy of the amplified filtered IF signal  152  may be varied within the predefined range to maintain desired signal strength and/or quality of service (QOS) in response to changes in the input signal  102 .  
      In the depicted embodiment, an analog to digital (A/D) converter (ADC)  160  converts the amplified filtered IF signal  142  into a digital signal  162 . In a non-depicted, exemplary embodiment, the ADC  160  may be implemented as a delta sigma signal converter. Although the amplified filtered IF signal  142  is illustrated as a non-quadrature baseband A/D conversion, it is understood that alternative receiver architectures such as receiver with quadrature baseband A/D conversion and zero-IF or low-IF direct conversion with quadrature A/D conversion are contemplated.  
      In the depicted embodiment, an automatic integrated controller (AICTR)  170  monitors the digital signal  162 . The digital signal  162  may include data and/or information indicative of the QOS and/or signal strength such as a received signal strength indicator (RSSI). The RSSI may be identified by a particular bit sequence of the digital signal.  162 . In a particular embodiment, the AICTR  170  includes a gain controller (GC)  172  for controlling amplitude of an input signal  102  by maintaining the amplitude within a predefined range, a frequency controller (FC)  174  to control a frequency of a local oscillator (LO) signal  122 , and a low pass filter controller (LPFC)  176  to control LPF  140  filter characteristics such as corner frequency and/or roll-off slope. The gain controller  172  may control gain factors for one or more amplifiers included in the receiver  100 .  
      Specifically, the AICTR  170  provides the LO control signal  124  to adjust the variable frequency of the LO signal  122 , the LNA control signal  114  to adjust a gain of the LNA  110 , the VGA control signal  154  to adjust the amplitude of the filtered IF signal  142 , and the LPF control signal  144  to adjust the filter characteristics in response to the digital signal  162 . In a non-depicted exemplary embodiment, the AICTR  170  may be implemented in a digital signal processor (DSP).  
      A gain or amplitude of the amplified filtered IF signal  152  is controlled by the AICTR  170  to operate the receiver  100  substantially close to saturation but without entering saturation. For example, by adjusting the gain to a value less than a threshold value at which a close-in interferer signal would saturate the receive path. The effective gain of the amplified filtered IF signal  152  is further improved without forcing the receiver  100  to operate in a saturated mode by increasing or decreasing the IF frequency f IF  of the IF signal  132  as described with reference to  FIG. 2 .  
       FIG. 2  is a graphical diagram illustrating amplitude versus frequency response characteristics  200  of the receiver  100  described with reference to  FIG. 1 , according to an embodiment. As described earlier, the input signal  102  includes the signal of interest, initially at a carrier frequency f c  and downconverted to the frequency f IF , is illustrated by a graph  210 . The interfering signal having a frequency f INT    224  is illustrated by a graph  220 . Frequency response characteristics of the LPF  140  filter are illustrated by a graph  230 . The LPF  140  filter has an adjustable corner frequency of f 3dB    232  and has an adjustable slope S  234 . As illustrated, amplitude of the graph  220  may be greater than amplitude of the graph  210  by a factor of approximately 70 dB to 80 dB as is the case in a GSM receiver. The Y-axis represents f IF  having a frequency value of zero (also referred to as zero-IF or DC value).  
      As the value of the f IF  is reduced and approaches a DC value, the graph  210  shifts towards the Y-axis and is illustrated by a graph  212 . The f IF  frequency may be reduced to have a low value by either increasing the variable frequency of the LO signal  122  (for a low-side injection) or decreasing the variable frequency of the LO signal  122  (for a high-side injection). The IF frequency f IF  may be reduced to less than zero by continually increasing frequency of the LO signal  122  in the low side injection. The IF frequency f IF  may be made larger than zero by continually increasing frequency of the LO signal  122  in the high side injection. The reduction in f IF  also shifts the graph  220  away from the Y-axis and is illustrated by a graph  222 . In a particular embodiment, an adjustment of the IF frequency f IF  is varied in accordance with the attenuation desired. The LO signal  122  frequency may be increased or decreased accordingly to operate the receiver substantially close to saturation but avoiding saturation. When a gain reduction is desired (e.g., when a point is reached where a close-in interferer may saturate the receive path), then instead of reducing the gain, the AICRT  170  reduces the IF frequency f IF  of the receiver  100 . The reduction in f IF  results in additional filtering at the interferer frequency f INT ,  224  as is the case with graph  222 . Thus, the shift of the graph  210  towards the Y-axis and graph  220  away from the Y-axis also provides a small gain to the signal of interest, while concurrently providing a higher rejection or attenuation to the large interferers.  
      In a particular embodiment, similar results and/or further improvements to the performance of the receiver  100  may also be obtained by adjusting the corner frequency f 3dB    232  and/or the slope S  234 . That is, by lowering the corner frequency f 3dB    232  and/or by increasing the slope S  234 , a small gain may be provided to the signal of interest, while concurrently providing a higher rejection or attenuation to the large interferers.  
      Receivers having a low value of IF frequency f IF  avoid the DC offset problems and are sensitive to 1/f noise associated with traditional zero-IF receivers. The technique of adjusting amplifier gain as well as the IF frequency f IF  implemented in the AICTR  170  provides benefits of reducing the level of the largest interferers, e.g., the interfering signal illustrated by the graph  220 , and also decreasing the noise figure of the receiver  100  and thereby allowing a potential decrease in the receiver gain without increasing the original noise figure of the receiver. The AICTR  170  permits wider margins of errors about the AGC switching point and offer improved protection against process and temperature variations compared to traditional AGC techniques which provide the same attenuation to the signal of interest as well as the interfering signal. Therefore, the design considerations for analog implementation of AGC are less stringent in the receiver  100  compared to the traditional schemes, which may need more filtering and/or may need finer gain control steps.  
       FIG. 3  is a block diagram of an integrated receiver  300 , according to an embodiment. In the depicted embodiment, the integrated receiver  300  implements a low-IF direct conversion architecture with quadrature components and delta sigma converter to facilitate single chip implementation while improving receiver performance. The integrated receiver  300  adjusts the intermediate frequency (IF) f IF  and the gain to improve receiver performance without saturating the receiver, similar to the receiver  100  described with reference to  FIG. 1 . The integrated receiver  300  is better suited to provide full integration with a single chip implementation compared to continuous signal analog implementations, which may use bulkier components. In the depicted embodiment, the integrated receiver  300  is a quad band receiver operable to receive a first input signal  302 , a second input signal  304 , a third input signal  306  and a fourth input signal  308 .  
      Each one of the received signals  302 - 308  is amplified by a low noise amplifier (LNA), split into I/Q paths and converted to current domain using a transconductance amplifier (TA) stage. The current is then down-converted to a programmable low-IF frequency (e.g.,  100  kilohertz) and integrated on a sampling capacitor at the LO rate. Considering plus and minus sides, each of the received input signal is sampled at the Nyquist rate of the RF carrier. After initial decimation through a Sinc ((Sin x)/x function) filter response, a series of infinite impulse response filtering follows RF sampling for close-in interferer rejection. These signal processing operations are performed in a multitap direct sampling mixer (MTDSM). Following the MTDSM, a sigma delta ADC includes a front-end gain stage for amplification and conversion to a digital signal.  
      Specifically, the integrated receiver  300  includes an analog front end (AFE)  310  circuit and an analog back end (ABE)  320  circuit which are discrete-time analog signal processing circuits to down-convert, downsample, filter and A/D convert the received signals  302 - 308 . The AFE  310  includes low band (LB) and high band (HB) low noise amplifiers LNA LB and HB to receive the input signals  302 - 308 . The signal is split into l/Q components and provided to transconductance amplifiers TA LBI/TA LBQ and TA HBI/TA HBQ for conversion to current domain and amplification. A multi-tap direct-sampling mixer (MTDSM)  380  provides filtered I/Q signals  382  to the ABE  320 . The MTDSM  380  is a well known circuit that leverages the fast switching time and capacitor consistency to perform switched-capacitor filtering. The MTDSM  380  filters out most of the energy that is not of interest.  
      The ABE  320  performs amplification and A/D conversion. It includes continuous time amplifiers CTA LBI and CTA LBQ to receive the filtered I/Q signals  382  and passive sigma delta AND converter SD ADC for each I/Q channels. The ABE  320  provides a first digital signal  322  to a digital receiver (DRX)  330  to perform the downconversion to low-IF in digital domain. The digital receiver  330  provides RXI/RXQ  332  outputs to other devices such as a digital signal processor (DSP)  340  within the integrated receiver  300 . The RXI/RXQ  332  outputs may be communicated to the DSP  340  via a well known communication standard such as open core protocol (OCP).  
      In a particular embodiment, the DSP  340  includes control logic  350  to perform functions substantially similar to the AICTR  170  described with reference to  FIG. 1 . That is, the control logic  350  monitors RSSI information and perform AGC functions such as adjusting the intermediate frequency (IF) f IF  and the gain to improve receiver performance without saturating the receiver.  
      In the depicted embodiment, the DSP  340  provides a LO control signal  342  to adjust frequency of low band I/Q signals LOLBI/LOLBQ and LOHBI/LOHBQ, a LNA control signal  344  to adjust a gain of the LNA LB and LNA HB, an ABE gain control signal  346  to adjust gain of continuous time amplifiers CTA LBI and CTA LBQ, and a transconductance amplifier/mixer TA/MIX control signal  348  to adjust gain of TA LBI/TA LBQ and TA HBI/TA HBQ in response to receiving the RXI/RXQ  332  outputs.  
       FIG. 4  is a flow chart illustrating a method for performing automatic gain control (AGC) in a receiver, according to an embodiment. In step  410 , a gain of an output signal is adjusted in response to an input signal received by the receiver to operate the receiver substantially close to saturation but without saturating the receiver. In a particular embodiment, the receiver is substantially the same as the receiver  100  described with reference to  FIG. 1  and/or the integrated receiver  300  described with reference to  FIG. 3 . The input signal includes a signal of interest and an interfering signal. At step  420 , an intermediate frequency (IF) of the receiver is reduced to provide greater attenuation to the interfering signal compared to an attenuation for the signal of interest. In a particular embodiment, the IF is reduced by mixing the input signal having a first predefined frequency with a local oscillator (LO) signal having a variable second frequency, which is increased to reduce a difference between the first predefined frequency and the variable second frequency.  
      In an alternative embodiment, the IF f IF  is reduced by mixing the input signal having the first predefined frequency with the local oscillator (LO) signal having the variable second frequency, which is decreased to reduce a difference between the first predefined frequency and the variable second frequency. The value of IF frequency f IF  may be continuously varied from a positive value to a negative value. The variable second frequency is adjusted in accordance with the gain. For example, the variable second frequency is increased when the gain is increased to operate the receiver substantially close to the saturation.  
      Various steps described above may be added, omitted, combined, altered, or performed in different orders. For example, additional steps may be added to control filter characteristics such as corner frequency and slope. At step  430 , a corner frequency of a filter included in the receiver is adjusted to filter out predefined frequencies of the input signal. The adjustment to the corner frequency provides greater attenuation to the interfering signal compared to the attenuation for the signal of interest. In step  440 , a roll-off slope of a filter included in the receiver is adjusted to filter out predefined frequencies of the input signal. The adjustment to the roll-off slope provides greater attenuation to the interfering signal compared to the attenuation for the signal of interest.  
      Although illustrative embodiments have been shown and described, a wide range of modification, change and substitution is contemplated in the foregoing disclosure and in some instances, some features of the embodiments may be employed without a corresponding use of other features. Those of ordinary skill in the art will appreciate that the hardware and methods illustrated herein may vary depending on the implementation. For example, although the disclosure is described in the context of analog functions, this disclosure is not limited to use with analog technology; rather, it envisions use of analog (continuous time and discreet-time), digital and mixed mode signal processing technologies. As another example, although the disclosure is described in the context of a high-side injection receiver, the present disclosure is applicable in low-side injection receiver as well.  
      While the description focuses on radio devices based on the GSM standard, the present disclosure is applicable in other frequency bands using other technical standards, including proprietary standards. Therefore, the discussion should not be construed as limiting the present invention to GSM transceivers. For example, the present invention has application in global positioning systems (GPS), low-earth orbit satellite system based communications systems, geographic area wide wireless networks and other cellular based communications systems. The cellular based systems may include first, second, and third generation (and beyond) digital phone systems, time-division multiple access (TDMA), code-division multiple access (CDMA), Bluetooth technology along with other digital communications technologies operating at various carrier frequencies. Additionally, as described above, the transceiver device described in the present disclosure has application in wired transceivers as well.  
      The methods and systems described herein provide for an adaptable implementation. Although certain embodiments have been described using specific examples, it will be apparent to those skilled in the art that the invention is not limited to these few examples. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or an essential feature or element of the present disclosure.  
      The above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments which fall within the true spirit and scope of the present invention. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.