Apparatus for NTSC signal interference cancellation through the use of digital recursive notch filters

A television receiver for removing NTSC components, including an NTSC picture carrier component, an NTSC chrominance subcarrier component, and an NTSC audio carrier component, from a received television signal including a high definition television (HDTV) signal and for processing said high definition television signal for display, comprising:

• a tuner including means for receiving television signals and band-limiting said received television signals,
• a first bi-quadratic recursive digital filter, coupled to said tuner, having an adjustable notch at the carrier frequency of the NTSC picture carrier component of said received, band-limited television signals for isolating said NTSC picture carrier component, whereby said first bi-quadratic recursive digital filter independently adjusts the center frequency and gain of said adjustable notch to match both the frequency and amplitude of said NTSC picture carrier component, said first filter producing a phase shift of zero at said center frequency of said first filter's notch;
• a second bi-quadratic recursive digital filter, coupled to said tuner, having an adjustable notch at the subcarrier frequency of the NTSC chrominance component of said received, band-limited television signals for isolating said NTSC chrominance component, whereby said second bi-quadratic recursive digital filter independently adjusts the center frequency and gain of said adjustable notch to match both the frequency and amplitude of said NTSC chrominance component, said second bi-quadratic recursive digital filter producing a phase shift of zero at said center frequency of said second filter's notch;
• a third bi-quadratic recursive digital filter, coupled to said tuner, having an adjustable notch at the carrier frequency of the NTSC audio component of said received, band-limited television signals for isolating said NTSC audio component, whereby said third bi-quadratic recursive digital filter independently adjusts the center frequency and gain of said adjustable notch to match both the frequency and amplitude of said NTSC audio component, said third bi-quadratic recursive digital filter producing a phase shift of zero at said center frequency of said third bi-quadratic recursive digital filter's notch;
• a summing circuit, coupled to said first, second, and third bi-quadratic recursive digital filters and to said tuner, to subtract said isolated NTSC picture carrier, chrominance subcarrier, and audio carrier components from said received, band-limited television signals and to output said high definition television components, and
• a demodulator, coupled to the output of said summing circuit, to demodulate said high definition television components for display thereof.

A television receiver for removing an NTSC component of a received television signal including a high definition television (HDTV) signal and for processing said high definition television signal for display, comprising:

• a tuner including means for receiving television signals and band-limiting said received television signals,
• a recursive digital notch filter, coupled to said tuner, having an adjustable notch at the carrier frequency of said NTSC component of said received, band-limited television signals for isolating said NTSC component, said filter producing a phase shift of zero at said center frequency of said filter's notch, whereby said recursive digital notch filter independently adjusts the center frequency of said adjustable notch to match the frequency of said NTSC component;
• a summing circuit, coupled to said recursive digital notch filter and to said tuner, to subtract said isolated NTSC component from said received, band-limited television signals and to output said high definition television components, and
• a demodulator, coupled to said summing circuit, to demodulate said high definition television components for display thereof.

A filter for removing NTSC interference from a television signal, the filter comprising:

• an adjustable gain recursive digital notch filter having a notch centered at the carrier frequency of a preselected NTSC signal component of the television signal and adapted for coupling to a tuner for receiving the television signal, for isolating the preselected NTSC signal component from the received television signal and for outputting the isolated NTSC signal component;
• means for adjusting the gain of the recursive digital filter as a function of the power of the preselected NTSC signal component to a level whereat the amplitude of the isolated NTSC signal component output by the adjustable gain recursive digital notch filter approximates the amplitude of the preselected NTSC signal component;
• and
• a summing circuit adapted for coupling to the tuner and coupled to the recursive digital notch filter for receiving the isolated NTSC signal component and for subtracting the isolated NTSC signal component from the television signal.