Method and apparatus for automatic gain control and DC offset cancellation in quadrature receiver

A method for automatic gain control using an adjustable gain amplifier, the adjustable gain amplifier having an input port for receiving an input signal, a control port for receiving a gain control signal, and an output port for providing an output signal, the method comprising the steps of:

• downconverting frequency of said output signal to a baseband frequency so as to produce a baseband signal wherein a carrier frequency of said output signal is mapped to a baseband frequency offset by a predetermined margin from D.C.;
• suppressing D.C. feedthrough signals accompanying said baseband signal so as to provide a compensated baseband signal;
• generating a received power signal based on power of said compensated baseband signal;
• and
• integrating selectively a difference between said received power signal and a reference signal based on values of said error and gain control signals.

An automatic gain control apparatus for compensating for variations in received signal power, the automatic gain control apparatus comprising:

• an adjustable gain amplifier having an input port coupled to a received signal, an output port for generating an output signal having a frequency, and a control port for receiving a gain control signal;
• a downconverter coupled to the output port for downconverting the frequency of the output signal to produce a baseband signal having a baseband frequency, the downconverter mapping a carrier frequency of the output signal to a baseband frequency offset by a predetermined margin from D.C.;
• a filter, coupled to the downconverter, for removing D.C. offset errors and signal in the baseband signal to generate a filtered signal;
• a power detector, coupled to the filter, for generating a power level signal in response to a power of the filtered signal;
• and
• an integrator having a first input coupled to the power detector and a second input coupled to a reference signal, the integrator generating the gain control signal by selectively integrating a difference between the reference signal and the power level signal.

An automatic gain control apparatus for compensating for variations in received signal power, the automatic gain control apparatus comprising:

• an adjustable gain amplifier having an input port coupled to a received signal, an output port for generating an output signal having a frequency, and a control port for receiving an analog gain control signal;
• a downconverter, coupled to the output port, for downconverting the frequency of the output signal to produce at least one baseband signal having a baseband frequency, the downconverter mapping a carrier frequency of the output signal to a baseband frequency offset by a predetermined margin from D.C.;
• at least one analog to digital converter, each coupled to a different baseband signal of the at least one baseband signal, each analog to digital converter generating a digital representation of the respective baseband signal;
• a filter, coupled to the at least one analog to digital converter, for generating at least one filtered signal;
• a power detector coupled to the filter, the power detector generating a power level signal in response to the at least one filtered signal;
• an integrator, coupled to the power detector, for comparing the power level signal to a predetermined reference signal to generate an error signal, the integrator generating a digital gain control signal by selectively integrating the error signal in response to values of the error signal and the digital gain control signal;
• and
• a digital to analog converter coupled between the integrator and the adjustable gain amplifier, the digital to analog converter generating the analog gain control signal from the digital gain control signal.

A method for compensating for variations in received signal power in an automatic gain control apparatus having an adjustable gain amplifier, the adjustable gain amplifier having an input port coupled to a received signal, an output port for generating an output signal having a frequency, and a control port for receiving a gain control signal, the method comprising the steps of:

• downconverting the frequency of the output signal to produce a baseband signal having a baseband frequency;
• generating a filtered signal by removing D.C. offset errors and signal in the baseband signal;
• generating a power level signal in response to a power of the filtered signal;
• and
• generating a gain control signal by selectively integrating a difference between the power level signal and a reference signal.

A method for compensating for variations in received signal power in an automatic gain control apparatus having an adjustable gain amplifier, the adjustable gain amplifier having an input port coupled to a received signal, an output port for generating an output signal having a frequency, and a control port for receiving an analog gain control signal, the method comprising the steps of:

• downconverting the frequency of the output signal to produce at least one baseband signal having a baseband frequency;
• generating a digital representation of each respective baseband signal;
• generating at least one filtered signal by filtering the digital representations of the at least one baseband signal;
• generating a power level signal in response to the at least one filtered signal;
• comparing the power level signal to a reference signal to generate an error signal;
• generating a digital gain control signal by selectively integrating the error signal in response to values of the error signal and the digital gain control signal;
• and
• converting the digital gain control signal to the analog gain control signal.