Automatic gain control system

A method of processing a wideband signal comprising transmitted video and audio information including a desired channel signal comprising video and audio information transmitted according to any one of a variety of transmission standards, wherein the method comprises:

• performing analog filtering and analog amplification on a multi-channel signal derived from the wideband signal to produce a coarse channel signal, wherein the analog amplification includes using at least one analog Variable Gain Amplifier (VGA) for providing a variable amount of analog amplification;
• digitizing the coarse channel signal with an Analog to Digital Converter (ADC) to produce a digitized coarse channel signal;
• and
• generating a quasi peak measurement of the digitized coarse channel signal and utilizing the quasi peak measurement in a feedback loop to control amplification of the at least one analog VGA, wherein the quasi peak measurement is generated to track a first level when the desired channel signal is transmitted according to an analog transmission standard and a second level when the desired channel signal is transmitted according to a digital transmission standard;
• and
• selecting a reference level to provide a first amount of headroom between the root-mean-square value of the digitized coarse channel signal and a full scale range of the ADC during synchronizing intervals when the desired channel signal is transmitted according to the analog transmission standard and a second amount of headroom between the root-mean-square level of the digitized coarse channel signal and the full scale range of the ADC when the desired channel signal is transmitted according to the digital transmission standard wherein the second amount is greater than the first amount;
• wherein the method further comprises generating the quasi peak measurement to track the first level to be substantially equal to a mean square-level based on the digitized coarse channel signal during synchronizing intervals when the desired channel signal is transmitted according to the analog transmission standard and to track the second level to be substantially greater than the mean square level based on the digitized coarse channel signal when the desired channel signal is transmitted according to the digital transmission standard.

A receiver configured to process a wideband signal comprising transmitted video and audio information including a desired channel signal comprising video and audio information transmitted according to any one of a variety of transmission standards, wherein the receiver comprises:

• an analog processing block for filtering and amplifying a multi-channel signal derived from the wideband signal to produce a coarse channel signal;
• a plurality of analog variable gain amplifiers (VGAs) for providing a variable amount of analog amplification;
• an Analog to Digital Converter (ADC) coupled to the analog processing block stage for digitizing the coarse channel signal to produce a digitized coarse channel signal;
• and
• an analog gain control block configured to set an initial gain coefficient of at least one analog VGA of the plurality of analog VGAs based on a metric of the desired channel signal, the metric being selected in part depending on whether the desired channel signal is transmitted according to an analog or digital transmission standard, wherein the initial gain coefficient of the at least one analog VGA is set during calibration which comprises applying a plurality of gain coefficients to the at least one analog VGA, measuring a quality of the desired channel signal for the plurality of gain coefficients based on the metric and selecting from the plurality of gain coefficients a gain coefficient with a highest quality of the desired channel signal based on the metric;
• and
• an analog gain coefficient look-up table having the initial gain coefficients for the plurality of analog VGAs indexed according to channel signal, wherein, during operation, the analog gain control block is configured to set current gain coefficients of the plurality of analog VGAs using values in the analog gain coefficient look-up table based on the desired channel signal;
• wherein a current gain coefficient is obtained by measuring a first gain coefficient of the at least one analog VGA to achieve a desired power value for the coarse channel signal, and calculating a difference gain coefficient from the difference of the first and the initial gain coefficients, and, in use, measuring the power of the at least one analog VGA, calculating a third gain coefficient to achieve the desired power value and adjusting the third gain coefficient by the difference gain coefficient.

A method of processing a wideband signal comprising transmitted video and audio information including a desired channel signal comprising video and audio information transmitted according to any one of a plurality of transmission standards, wherein the method comprises:

• performing analog filtering and analog amplification on a multi-channel signal derived from the wideband signal to produce a coarse channel signal, wherein the analog amplification includes using a plurality of analog Variable Gain Amplifiers (VGAs) for providing a variable amount of analog amplification;
• digitizing the coarse channel signal with an Analog to Digital Converter (ADC) to produce a digitized coarse channel signal;
• and
• setting an initial gain coefficient of at least one analog VGA of the plurality of analog VGAs based on a metric of the desired channel signal, the metric being selected in part depending on whether the desired channel signal is transmitted according to an analog or digital transmission standard, wherein the initial gain coefficient of the at least one analog VGA is set during calibration which comprises applying a plurality of gain coefficients to the at least one analog VGA, measuring a quality of the desired channel signal for the plurality of gain coefficients based on the metric and selecting from the plurality of gain coefficients a gain coefficient with a highest quality of the desired channel signal based on the metric;
• generating a current gain coefficient by measuring a first gain coefficient of the at least one analog VGA to achieve a desired power value for the coarse channel signal, and calculating a difference gain coefficient from the difference of the first and the initial gain coefficients, and, in use, measuring the power of the at least one analog VGA, calculating a third gain coefficient to achieve the desired power value and adjusting the third gain coefficient by the difference gain coefficient;
• and
• using an analog gain coefficient lookup table having the initial gain coefficients for the plurality of analog VGAs indexed according to channel signal, wherein, during operation, the method comprises setting the current gain coefficients of the plurality of analog VGAs using values in the analog gain coefficient look-up table indexed by the desired channel signal.

An automatic gain control system for a receiver configured to process a wideband signal comprising transmitted video and audio information, wherein the automatic gain control system comprises:

• an analog gain control block configured to provide at least one analog gain control signal to control an amount of analog amplification applied by at least one analog Variable Gain Amplifier (VGA) in the receiver;
• and
• a digital gain control block configured to provide at least one digital gain control signal to control an amount of digital amplification applied by at least one digital Variable Gain Amplifier (VGA) in the receiver;
• wherein the digital gain control block is configured to set a gain coefficient of the at least one digital VGA based on a metric of a desired channel signal comprising transmitted video and audio information, the metric being one of Signal to Noise ratio, Signal to Noise plus distortion ratio and Bit Error Rate, the metric being selected in part depending on whether the desired channel signal is transmitted according to an analog or digital transmission standard;
• and
• wherein the analog gain control block is operable in first and second modes, wherein in the first mode the analog gain control block is configured to generate a quasi peak measurement of a digitized version of a desired channel signal comprising transmitted video and audio information and utilize the quasi peak measurement in a feedback loop to control the amplification of the at least one analog VGA, and in the second mode the analog gain control block is configured to set an initial gain coefficient of the at least one analog VGA based on a metric of the desired channel signal.

A method for automatic gain control in a receiver configured to process a wideband signal comprising transmitted video and audio information, wherein the method comprises:

• providing at least one analog gain control signal to control an amount of analog amplification applied by at least one analog Variable Gain Amplifier (VGA) in the receiver;
• controlling the gain of the at least one VGA using first and second modes, wherein in the first mode the method comprises generating a quasi peak measurement of a digitized version of a desired channel signal comprising transmitted video and audio information and utilizing the quasi peak measurement in a feedback loop to control the amplification of the at least one analog VGA, and in the second mode the method comprises setting an initial gain coefficient of the at least one analog VGA based on the metric of the desired channel signal;
• providing at least one digital gain control signal to control an amount of digital amplification applied by at least one digital Variable Gain Amplifier (VGA) in the receiver;
• and
• setting a gain coefficient of the digital VGA based on a metric of a desired channel signal comprising transmitted video and audio information, the metric being one of Signal to Noise ratio, Signal to Noise plus distortion ratio and Bit Error Rate, the metric being selected in part depending on whether the desired channel signal is transmitted according to an analog or digital transmission standard.