Automatic gain control system

摘要

Various embodiments are described herein for automatic gain control techniques that can be used by a universal television receiver that is capable of processing television channel signals broadcast according to a variety of analog and digital broadcast standards.

主权项

1. A receiver configured to process a wideband signal comprising transmitted video and audio information including a desired signal comprising video and audio information transmitted according to any one of a plurality 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; at least one analog variable gain amplifier (VGA) for providing a variable amount of analog amplification; an Analog to Digital Converter (ADC) coupled to the analog processing block for digitizing the coarse channel signal to produce a digitized coarse channel signal; and an analog gain control block configured to generate a quasi peak measurement of the digitized coarse channel signal and utilize the quasi peak measurement in a feedback loop to control the 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; wherein the analog gain control block is configured to generate 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; and wherein a reference level is selected to provide a first amount of headroom between the root-mean-square level of the digitized coarse channel signal and the 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 television channel signal is transmitted according to the digital transmission standard wherein the second amount is greater than the first amount.