Automatic gain control methods and apparatus suitable for use in OFDM receivers

An automatic gain control (AGC) circuit for a communication receiver, the AGC circuit comprising:

• an amplifier for amplifying received signals including pilot tones to produce amplified received signals;
• an analog-to-digital (A/D) circuit connected to the amplifier;
• and
• at least one processor connected to the A/D circuit and the amplifier, the at least one processor for adjusting a gain of the amplifier in response to clipping of the amplified received signals by the A/D circuit, the at least one processor also for adjusting a gain of the amplifier in response to a power of one or more frequency components of the pilot tones exceeding a limit.

An automatic gain control (AGC) circuit for a communications receiver, the AGC circuit comprising:

• an amplifier for amplifying received signals to produce amplified received signals;
• an analog-to-digital (A/D) circuit for generating a plurality of time domain samples of the amplified received signals;
• a boundary check processor for determining a level of signal clipping of the amplified received signals based on a time sample signal level of the plurality of time domain samples and providing a control signal in accordance with the level of clipping;
• a transform processor for converting the time domain samples to multiple frequency domain samples;
• a digital signal processor (DSP) for determining a power level of the multiple frequency domain samples and providing another control signal in accordance with a relationship between the power level and another threshold;
• and
• a switch for directing the control signal and the another control signal to the amplifier in accordance with a clock signal.

A remote unit for wireless communication with a base station using communication signals, the remote unit comprising:

• an amplifier for amplifying received communication signals to produce amplified received communication signals;
• an analog-to-digital (A/D) circuit for generating a plurality of time domain samples of the amplified received communication signals;
• and
• at least one processor connected to the A/D circuit and the amplifier, the at least one processor for adjusting a gain of the amplifier in accordance with a relationship between a threshold and a time sample signal level of the plurality of time domain samples, the at least one processor for adjusting the gain of the amplifier in accordance with another relationship between another threshold and a frequency sample signal level of frequency sample values associated with a plurality of pilot tones of the communication signals.

A remote unit for wireless communication with a base station using communication signals, the remote unit comprising:

• an amplifier for amplifying received communication signals to produce amplified received communication signals;
• an analog-to-digital (A/D) circuit for generating a plurality of time domain samples of the amplified received communication signals;
• a boundary check processor for determining a level of signal clipping of the amplified received communication signals based on a time sample signal level of the plurality of time domain samples and providing a control signal in accordance with the level of clipping;
• a transform processor for converting the time domain samples to multiple frequency domain samples;
• a digital signal processor (DSP) for determining a power level of the multiple frequency domain samples and providing another control signal in accordance with a relationship between the power level and another threshold;
• and
• a switch for directing the control signal and the another control signal to the amplifier in accordance with a clock signal.

A communications receiver, comprising:

• an amplifier for amplifying a received signal and configured to receive at least one control signal;
• an analog-to-digital converter for converting the received signal into a digital signal in the time domain;
• and
• an automatic gain control (AGC) circuit coupled with the amplifier and the analog-to-digital converter;
• wherein the automatic gain control circuit is configured to provide a first and a second control signal to control amplification gain of the amplifier;
• wherein the first control signal is varied in response to clipping of the time domain digital signal in the time domain;
• and
• wherein the second control signal is varied in response to frequency domain power level of predetermined portions of the digital signal.

A method of processing a signal, comprising:

• amplifying a waveform via an amplifier;
• sampling the waveform at a predetermined sampling rate to generate digital time domain samples;
• determining whether the digital time domain samples are clipped;
• providing first gain adjustment control signals to the amplifier if the time domain samples are clipped;
• converting the time domain samples into frequency domain samples;
• determining whether fading of the signal occurred by analysis of the frequency domain samples;
• and
• providing second gain adjustment control signals to the amplifier if fading occurred.

A method of holding the magnitude of a waveform close to the full dynamic range of an analog to digital converter, comprising:

• providing a communication signal to an amplifier;
• amplifying the communication signal to convert the communication signal to an amplified communication signal;
• providing the amplified communication signal to an analog to digital converter;
• performing analog to digital conversion of the communication signal to convert the communication signal to a digital time domain signal;
• determining whether the digital time domain signal is clipped;
• selectively providing first gain adjustment control signals to the amplifier at a first interval if the digital time domain signal is clipped;
• converting the digital time domain signal into a frequency domain signal;
• selectively providing second gain adjustment control signals to the amplifier at a second interval if the power of predetermined portions of the frequency domain signal are outside a predefined threshold level;
• and
• adjusting the gain of the amplifier in response to the first and second control signals.