Method and circuit for channel filtering of analog or digitally modulated TV signals

• US 20060103766A1
• Filed: 11/14/2005
• Published: 05/18/2006
• Est. Priority Date: 11/12/2004
• Status: Active Grant

• Current Assignee: Entropic Communications Incorporated (Maxlinear Incorporated)
• Original Assignee: Micronas Gmbh (TDK Corporation)
• Inventors: Temerinac, Miodrag, Fiesel, Hans
• Granted Patent: US 7,593,065 B2
• Time in Patent Office: Days
• US Class Current: 348/726
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 21/4382 Demodulation or channel decoding, e.g. QPSK demodulation analog front ends or means for connecting modulators, demodulators or transceivers to a transmission line H04L27/0002
• CPC Class Codes: H04N 5/455 Demodulation-circuits
• CPC Class Codes: H04N 5/46 for receiving on more than one standard at will deflecting circuits of multi-standard receivers H04N3/27

Abstract

The invention relates to a circuit for channel filtering of an analog or digitally modulated TV signal (125), comprising a video signal (125b), a sound signal (125a), and a video carrier signal (BT) having a video carrier frequency (f_BT) at which the TV signal (125) is converted to an intermediate frequency (2^nd IF) generating an intermediate frequency signal (S_IF). In order to suppress interference signals from adjacent TV channels, according to the invention the intermediate frequency signal (S_IF) is demodulated with a signal (S(f_BT; 0°)) at a video carrier frequency (f_BT) into an in-phase signal (I), and with a signal (S(f_BT; 90°)) shifted in phase by a phase angle π/2 relative to the signal (S(f_BT; 0°)) and at a video carrier frequency (f_BT) into a quadrature signal (Q), for example, by an I/Q demodulator (3). The in-phase signal (I) is filtered by a first Hilbert filter (HF-I) of a Hilbert filter pair (HF-I, HF-Q) having an even symmetrical impulse response (h₁(L−n)=h₁(n)) in order to obtain a Hilbert-filtered in-phase signal (I_H). In analogous fashion, the quadrature signal (Q) is filtered by a second Hilbert filter (HF-Q) of the Hilbert filter pair (HF-I, HF-Q). having an uneven symmetrical impulse response in order to obtain a Hilbert-filtered quadrature signal (Q_H). The Hilbert-filtered quadrature signal (Q_H) is added, for example, by an adder (21) to the Hilbert-filtered in-phase signal (I_H) in order to obtain a video output signal (S_Video). Alternatively or in addition, according to the invention, the Hilbert-filtered quadrature signal (Q_H) is subtracted from the Hilbert-filtered in-phase signal (I_H), for example, by a subtractor, in order to obtain a sound output signal (S_Sound′).

Claims

1. A method for channel filtering of an analog or digitally modulated TV signal (125), comprising a video signal (125b), a sound signal (125a), and a video carrier signal (BT) having a video carrier frequency (f_BT) at which the TV signal (125) is converted to an intermediate frequency (2^nd IF) generating an intermediate frequency signal (S_IF), where the intermediate frequency (S_IF) is I/Q-demodulated with a signal (S(f_BT;

0°

)) at a video carrier frequency (f_BT) into an in-phase signal (I), and with a signal (S(f_BT;

90°

)) shifted in phase by a phase angle π

/2 relative to the signal (S(f_BT;

0°

)) and at a video carrier frequency (f_BT) into a quadrature signal (Q);

that the in-phase signal (I) is filtered by a first Hilbert filter (HF-I) of a Hilbert filter pair (HF-I, HF-Q) having an even symmetrical impulse response (h₁(L−

n)=h₁(n)) in order to obtain a Hilbert-filtered in-phase signal (I_H); and

that the quadrature signal (Q) is filtered by a second Hilbert filter (HF-Q) of the Hilbert filter pair (HF-I, HF-Q) having an uneven symmetrical impulse response in order to obtain a Hilbert-filtered quadrature signal (Q_H);

that the Hilbert-filtered quadrature signal (Q_H) is added to the Hilbert-filtered in-phase signal (I_H) in order to obtain a video output signal (S_Video); and

/or that the Hilbert-filtered quadrature signal (Q_H) is subtracted from the Hilbert-filtered in-phase signal (I_H) in order to obtain a sound output signal (S_Sound′

).

2. The method of claim 1, where the intermediate frequency signal (S_IF) is generated by converting a video carrier (BT*) from the lower side channel (126, 126′

) to zero frequency (f_BT*=0).

3. The method of claim 1, where the intermediate frequency signal (S_IF) is bandpass-filtered before the I/Q demodulation.

4. The method of claim 3, where the bandpass filtering is implemented digitally at a sampling frequency (f_s).

5. The method of claim 3, where the bandpass filtering is used to suppress residual interference (f_BT*) from the lower side channel (126′

).

6. The method of claim 5, where the bandpass filtering has a passband that extends between a frequency (f) greater than the frequency (f_BT*=0;

133) to which the video carrier (BT*) of the lower side channel (126′

) has been converted and a frequency (f) smaller than half the sampling frequency (f_s/2;

     134).

7. The method of claim 5, where the bandpass filtering has a zero value (133) at the frequency (f_BT*=0) to which the video carrier (BT*) of the lower side channel (126′

) has been converted, and/or that the bandpass filtering has a zero value (134) at half the sampling frequency (f_s/2).

8. The method of claim 1, where the in-phase signal (I) is low-pass-filtered before the Hilbert filtering and/or that the quadrature signal (Q) is low-pass-filtered before the Hilbert filtering.

9. The method of claim 1, where the low-pass filtering of the in-phase signal (I) and/or the low-pass filtering of the quadrature signal (Q) is used to suppress unwanted mixing products around the second harmonic of the video carrier (f_BT) from the I/Q demodulation.

10. The method of claim 9, where the low-pass filtering of the in-phase signal (I) has a passband (136) that extends up to a frequency (f) corresponding to a channel bandwidth (B) of the TV signal, and/or that the low-pass filtering of the quadrature signal (Q) has a passband (136) that extends up to a frequency (f) corresponding to a channel bandwidth (B) of the TV signal.

11. The method of claim 9, where the low-pass filtering of the in-phase signal (I) has a zero value (139) at a frequency (2f_BT−

B) corresponding to double the video carrier frequency (2f_BT) minus the channel bandwidth (B)

12. The method of claim 1, where the Hilbert filtering is used to suppress interference products from an upper side channel (127′

), and/or that the phase relationship, in particular, the sign of the video signal and sound signal components in the in-phase signal (I) and quadrature signal (Q), are synchronized so as to produce the separation into the video output signal (S_Video) and the sound output signal (S_Sound) based on the sum of the Hilbert-filtered in-phase signal (I_H) and Hilbert-filtered quadrature signal (Q_H), or on the difference taken between the Hilbert-filtered in-phase signal (I_H) and Hilbert-filtered quadrature signal (Q_H).

13. The method of claim 12, where the Hilbert filtering of the in-phase signal (I) has a passband (137) that extends up to an upper frequency (f) corresponding to the channel bandwidth (B), and/or that the Hilbert filtering of the quadrature signal (Q) has a passband (138a, 138b) that extends up to an upper frequency (f) corresponding to the channel bandwidth (B).

14. The method of claim 12, where the Hilbert filtering of the quadrature signal (Q) has a passband (138a, 138b) that extends up to a lower frequency (f) corresponding to a residual bandwidth (F_R).

15. The method of claim 14, where the Hilbert filtering of the quadrature signal (Q) between a frequency corresponding to a bandwidth (BB) of the video signal and a frequency corresponding to a channel bandwidth (B) has a transfer function (H_Q=−

A_Q) with the sign inverted, as compared with the transfer function (H_Q=A_Q) between the residual frequency (f_R) and a frequency corresponding to a bandwidth (BB) of the video signal.

16. The method of claim 12, where the Hilbert filtering of the in-phase signal (I) has a zero value (139) at a frequency (2f_BT−

B) corresponding to double the video carrier frequency (2f_BT) minus the channel bandwidth (B), and/or the Hilbert filtering of the quadrature signal (Q) has a zero value (139) at a frequency (2f_BT−

B) corresponding to double the video carrier frequency (2f_BT) minus the channel bandwidth (B), and/or that the Hilbert filtering of the quadrature signal (Q) has a zero value (139) at a frequency corresponding to a bandwidth (BB) of the video signal.

17. The method of claim 1, where the sound signal (S_Sound′

) is high-pass-filtered in order to obtain a filtered sound output signal (S_Sound).

18. The method of claim 17, where the high-pass filtering suppresses residual interference (TT*) from a lower side channel (126′

).

19. A circuit for channel filtering of an analog or digitally modulated TV signal (125), comprising a video signal (125b), a sound signal (125a), and a video carrier signal (BT) having a video carrier frequency (f_BT) at which the TV signal (125) is converted to an intermediate frequency (2^nd IF) generating an intermediate frequency signal (S_IF), where an I/Q demodulator (3) is provided which is designed to demodulate the intermediate frequency (S_IF) with a signal (S(f_BT;

00)) at a video carrier frequency (f_BT) into an in-phase signal (I), and with a signal (S(f_BT;

90°

)) shifted in phase by a phase angle π

/2 relative to the signal (S(f_BT;

0°

)) and at a video carrier frequency (f_BT) into a quadrature signal (Q);

that a Hilbert filter pair (HF-I, HF-Q) is provided with a first Hilbert filter (HF-I) having a first even symmetrical impulse response (h₁(L−

n)=h₁(n)) and a second Hilbert filter (HF-Q) having a second uneven symmetrical response (h_Q(L−

n)=−

h_Q(n));

wherein the first Hilbert filter (HF-I) is designed to filter the in-phase signal (I) in order to obtain a Hilbert-filtered in-phase signal (I_H); and

whereby the second Hilbert filter (HF-Q) is designed to filter the quadrature signal (Q) in order to obtain a Hilbert-filtered quadrature signal (Q_H);

that an adder (21) is provided which is designed to add the Hilbert-filtered quadrature signal (Q_H) to the Hilbert-filtered in-phase signal (I_H) in order to obtain a video output signal (S_Video); and

/or that a subtractor (22) is provided which is designed to subtract the Hilbert-filtered quadrature signal (Q_H) from the Hilbert-filtered in-phase signal (I_H) in order to obtain a sound output signal (S_Sound′

).

20. The circuit of claim 19, comprising means for generating the intermediate frequency (S_IF) by converting a video carrier (BT*) from a lower side channel (126, 126′

) to zero frequency (f_BT*=0).

21. The circuit of claim 19, comprising a bandpass filter (BPF) connected on the input side of the I/Q demodulator (3) to bandpass-filter the intermediate frequency signal (S_IF) before the I/Q demodulation.

22. The circuit of claim 21, where the bandpass filter (BPF) bandpass filters digitally at a sampling frequency (f_s).

23. The circuit of claim 21, where the bandpass filter (BPF) suppresses residual interference (f_BT*) from the lower side channel (126′

).

24. The circuit of claim 23, where the bandpass filter (BPF) has a passband (135) that extends between a frequency (f) that is greater than the frequency (f_BT*=0;

133) to which the video carrier (BT*) of the lower side channel (126′

) has been converted and a frequency (f) that is smaller than half the sampling frequency (f_s)/2;

     134).

25. The circuit of claim 23, where the bandpass filter (BPF) has a zero value (133) at the frequency (f_BT*=0) to which the video carrier (BT*) of the lower side channel (126′

) has been converted, and/or that the bandpass filter (BPF) has a zero value (134) at half the sampling frequency.

26. The circuit of claim 19, comprising a low-pass filter (TPF-I) that filters the in-phase signal (I) before the Hilbert filtering.

27. The circuit of claim 26, where the low-pass filter (TPF-I) attenuates mixing products around the second harmonic of the video carrier (f_BT) from the I/Q demodulation.

28. The circuit of claim 27 where the low-pass filter (TPF-I) has a passband (136) that extends up to a frequency (f) corresponding to a channel bandwidth (B) of the TV signal, and/or that the low-pass filter (TPF-Q) for the quadrature signal (Q) has a passband (136) that extends up to a frequency (f) corresponding to a channel bandwidth (B) of the TV signal.

29. The circuit of claim 27, where the low-pass filter (TPF-I) for the in-phase signal (I) has a zero value (139) at a frequency (2f_BT−

B) corresponding to double the video carrier frequency (2f_BT) minus the channel bandwidth (B).

30. The circuit of claim 19, where the Hilbert filter pair (HF-I, HF-Q) suppresses interference products from an upper side channel (127′

), and/or that the Hilbert filter pair (HF-I, HF-Q) is designed to synchronize the phase relationship, in particular, the sign, of video signal and sound signal components in the in-phase signal (I) and in the quadrature signal (Q) so as to produce the separation into the video output signal (S_Video) and the sound output signal (S_Sound) based on the sum of the Hilbert-filtered in-phase signal (I_H) and Hilbert-filtered quadrature signal (Q_H), or on the difference taken between the Hilbert-filtered in-phase signal (I_H) and Hilbert-filtered quadrature signal (Q_H).

31. The circuit of claim 30, where the Hilbert filter (HF-I) for the in-phase signal (I) has a passband (137) that extends up to an upper frequency (f) corresponding to the channel bandwidth (B), and/or that the Hilbert filter (HF-Q) for the quadrature signal (Q) has a passband (138a, 138b) that extends up to an upper frequency (f) corresponding to the channel bandwidth (B).

32. The circuit of claim 30, where the Hilbert filter (HF-Q) for the quadrature signal (Q) has a passband (138a, 138b) that extends up to a lower frequency (f) corresponding to a residual frequency (f_R).

33. The circuit of claim 32, where the Hilbert filter (HF-Q) for the quadrature signal (Q) between a frequency corresponding to a bandwidth (BB) of the video signal and a frequency corresponding to channel bandwidth (B) has a transfer function (H_Q=−

A_Q) with the sign inverted, as compared with the transfer function (H_Q=A_Q) between the residual frequency (f_R) and a frequency corresponding to a bandwidth (BB) of the video signal.

34. The circuit of claim 30, where the Hilbert filter (HF-I) for the in-phase signal (I) has a zero value (139) at a frequency (2f_BT−

B) corresponding to double the video carrier frequency (2f_BT) minus the channel bandwidth (B), and/or that the Hilbert filter (HF-Q) for the quadrature signal (Q) has a zero value (139) at a frequency (2f_BT−

B) corresponding to double the video carrier frequency (2f_BT) minus the channel bandwidth (B), and/or that the Hilbert filter (HF-Q) for the quadrature signal (Q) has a zero value (139) at a frequency corresponding to a bandwidth (BB) of the video signal.

35. The circuit of claim 19, comprising a high-pass filter (HPF) to high-pass-filter the sound output signal (S_Sound′

) in order to obtain a filtered sound output signal (S_Sound).

36. The circuit of claim 35, where the high-pass filter (HPF) suppresses residual interference (TT*) from a lower side channel (126′

).