Using intercarrier signals for detecting NTSC interference in digital TV receivers

A receiver for receiving a digital television signal susceptible to being accompanied by co-channel interfering NTSC analog television signal, said receiver comprising:

• a tuner for selecting said digital television signal from one of channels at different locations in a frequency band and converting said selected digital television signal to generate a converted digital television signal in a prescribed intermediate-frequency band;
• a first intermediate-frequency amplifier chain for generating, as a respective output signal therefrom, an amplified response to said converted digital television signal;
• digital signal detection circuitry for detecting baseband symbol code signal responsive to said output signal from said first intermediate-frequency amplifier chain, which baseband symbol code signal includes artifacts of said co-channel interfering NTSC analog television signal when it accompanies said digital television signal selected by said tuner;
• intercarrier sound signal detection circuitry for detecting, in response to said digital television signal selected by said tuner, an intercarrier sound signal attributable to said co-channel interfering NTSC analog television signal accompanying said digital television signal selected by said tuner;
• an intercarrier amplitude detector for detecting the amplitude of said intercarrier sound signal attributable to said co-channel interfering NTSC analog television signal and generating an intercarrier amplitude detector response;
• decision circuitry, responsive to said intercarrier amplitude detector response, for supplying a decision signal indicative of whether or not said co-channel interfering NTSC analog television signal has sufficient energy to be likely to prevent symbol decoding of said baseband symbol code signal with less than a prescribed bit error rate;
• and
• symbol decoding circuitry for decoding said baseband symbol code signal, said symbol decoding circuitry responsive to said decision signal for comb filtering said baseband symbol code signal to suppress said artifacts of said co-channel interfering NTSC analog television signal only when said decision signal indicates said co-channel interfering NTSC analog television signal has sufficient energy to be likely to prevent symbol decoding of said baseband symbol code signal with less than a prescribed bit error rate.