Integrated IF SAW filter in baseband digital design for analog TV (or hybrid) tuner
View Patent ↗A filter for processing a digital TV composite signal having a video component and an audio component includes a digital video filter and a digital audio filter. The digital video filter includes a lowpass finite impulse response (FIR) filter, an up-mixer, an asymmetric filter for compensating a Nyquist slope of the video component, and a down-mixer connected in this order. The digital audio filter includes an audio down-mixer, a decimated FIR filter, an enhancing FIR filter, an interpolated FIR filter, and an audio up-mixer. These components are connected in series. Optionally, the decimating FIR filter is decimated by an integer decimation factor M, and the interpolated FIR filter is interpolated by an integer factor N. The integer M and N may have the same value.
1. A filter for processing a digital television (TV) composite signal having a video component and an audio component, the filter comprising:
an input terminal for receiving the digital TV composite signal;
a first lowpass filter coupled to the input terminal, the first lowpass filter being configured to pass through the video component;
a digital video filter coupled to the lowpass filter and being configured to process the video component, the digital video filter comprising:
a first mixer configured to frequency shift the video component by a first frequency offset;
a digital highpass filter responsive to the first mixer and configured to compensate a Nyquist slope of the first frequency-shifted video component; and
a second mixer responsive to the digital highpass filter; said first mixer, said digital highpass filter and said second mixer being coupled in series;
a third mixer configured to frequency shift the digital TV composite signal by a first frequency amount; and
a digital audio filter configured to receive the frequency shifted digital TV composite signal.
2. The filter of claim 1 , wherein the first lowpass filter comprises a first finite impulse response (FIR) filter.
3. The filter of claim 1 , wherein:
the second mixer mixes the Nyquist compensated video component by a second frequency offset to obtain a second frequency-shifted and Nyquist compensated video component.
4. The filter of claim 3 , wherein the sum of the first frequency offset and the second frequency offset is substantially equal to zero.
5. The filter of claim 3 , wherein the first and second frequency offsets are associated with a picture carrier frequency and a third frequency offset.
6. The filter of claim 5 , wherein the third frequency offset is about 0.75 MHz.
7. The filter of claim 1 , wherein the digital audio filter comprises:
a second lowpass filter configured to pass through the audio component;
a decimator configured to reduce a first sampling rate of the audio component by a factor M;
a second FIR filter configured to enhance the reduced sampling rate audio component;
an interpolator configure to increase the enhanced and sampling-rate audio reduced audio component by a factor N; and
a third FIR filter configured to output an audio signal.
8. The filter of claim 7 , wherein the factors M and N are positive integer.
9. The filter of claim 7 , wherein the factors M and N are equal.
10. The filter of claim 7 , wherein the digital audio filter further comprises a fourth mixer configured to frequency shift the audio signal by a second frequency amount.
11. The filter of claim 10 , wherein the second frequency amount is associated with a sound carrier frequency.
12. The filter of claim 7 , wherein the digital audio filter further comprises a first up-converter configured to up-convert the audio signal to an audio intermediate frequency.
13. The filter of claim 1 , wherein the first frequency amount is associated with a sound carrier frequency.
14. The filter of claim 1 further comprising a second up-converter configured to up-convert the processed video component to a video intermediate frequency.