Quadratic nyquist slope filter

• US 20030223017A1
• Filed: 09/30/2002
• Published: 12/04/2003
• Est. Priority Date: 05/28/2002
• Status: Active Grant

• Current Assignee: Rfstream Corporation
• Original Assignee: Rfstream Corporation
• Inventors: Utsunomiya, Kimitake, Kamata, Takatsugu
• Granted Patent: US 7,199,844 B2
• Time in Patent Office: Days
• US Class Current: 348/726
• CPC Class Codes: H03D 1/2245 using two quadrature channels H03D1/2209 takes precedence

Abstract

A television demodulator circuit, for use in a television receiver, generates baseband video and audio outputs from a television signal, such as an intermediate frequency television signal. The I, Q demodulator circuit mixes the television signal with an in-phase (“I”) local oscillator signal and a quadrature phase (“Q”) local oscillator signal at the tuned frequency to generate baseband I and Q signals. The baseband I and Q signals are input to low pass filters and a Nyquist slope filter. The Nyquist slope filter generates, for the baseband I and Q signals, a Nyquist slope response and attenuates channels adjacent to the tuned television channel. The Nyquist slope filter comprises a transfer function with at least two zero crossings, so as to provide a notch filter response for attenuation of a television channel adjacent to the tuned television channel. For example, the transfer function may have three zero crossings to attenuate a sound carrier frequency, a color carrier frequency, and a picture frequency for the television channel adjacent to the tuned television channel. The transfer function, expressed in the S domain, comprises an all-pass fractional transfer function with a real number in the numerator and a complex number in the denominator. A television receiver that incorporates the I, Q demodulator circuit is disclosed.

Claims

1. A television demodulator circuit comprising:

I, Q demodulator for receiving a television signal and for mixing the television signal with an in-phase (“

I”

) local oscillator signal and a quadrature phase (“

Q”

) local oscillator signal at a tuned television channel to generate a baseband I signal and a baseband Q signal;

low pass filter, coupled to the I, Q demodulator, for filtering the baseband I signal and baseband Q signal; and

Nyquist slope filter for receiving the baseband I signal and baseband Q signal and for generating a video signal by generating a Nyquist slope response and by attenuating channels adjacent to the tuned television channel.

2. The television demodulator circuit as set forth in claim 1, wherein the Nyquist slope filter comprises a transfer function with at least two zero crossings, so as to provide a notch filter response for attenuation of a television channel adjacent to the tuned television channel.

3. The television demodulator circuit as set forth in claim 2, wherein the transfer function with at least two zero crossings comprises transfer function with a zero crossing at a sound carrier frequency for the television channel adjacent to the tuned television channel.

4. The television demodulator circuit as set forth in claim 2, wherein the transfer function with at least two zero crossings comprises a transfer function with three zero crossings to attenuate a sound carrier frequency, a color carrier frequency, and a picture frequency for the television channel adjacent to the tuned television channel.

5. The television demodulator circuit as set forth in claim 1, wherein the transfer function comprises an all-pass fractional transfer function.

6. The television demodulator circuit as set forth in claim 1, wherein the transfer function comprises a real number in the numerator and a complex number in the denominator.

7. The television demodulator circuit as set forth in claim 1, wherein the Nyquist slope filter comprises inverters, such that a transfer function for the Nyquist slope filter comprises terms of the numerator with the same sign.

8. The television demodulator circuit as set forth in claim 1, wherein the low pass filter comprises a low pass filter with a Butterworth response.

9. A television receiver comprising:

downconverter circuit for receiving a radio frequency (“

RF”

) television signal, and for generating an intermediate frequency (“

IF”

) television signal;

demodulator circuit, coupled to the downconverter circuit, for receiving the IF television signal and for generating a video signal, the demodulator circuit comprising;

I, Q demodulator for receiving a television signal and for mixing the television signal with an in-phase (“

I”

) local oscillator signal and a quadrature phase (“

Q”

) local oscillator signal at a tuned television channel to generate a baseband I signal and baseband Q signal;

low pass filter, coupled to the I, Q demodulator, for filtering the baseband I signal and Q signal; and

Nyquist slope filter for receiving the baseband I signal and baseband Q signal and for generating a video signal by generating a Nyquist slope response and by attenuating channels adjacent to the tuned television channel.

10. The television receiver as set forth in claim 9, wherein the downconverter circuit comprises a double down conversion circuit.

11. The television receiver as set forth in claim 9, wherein the downconverter circuit comprises a single down conversion circuit.

12. The television receiver as set forth in claim 9, wherein the Nyquist slope filter comprises a transfer function with at least two zero crossings, so as to provide a notch filter response for attenuation of a television channel adjacent to the tuned television channel.

13. The television receiver as set forth in claim 12, wherein the transfer function with at least two zero crossings comprises transfer function with a zero crossing at a sound carrier frequency for the television channel adjacent to the tuned television channel.

14. The television receiver as set forth in claim 12, wherein the transfer function with at least two zero crossings comprises a transfer function with three zero crossings to attenuate a sound carrier frequency, a color carrier frequency, and a picture frequency for the television channel adjacent to the tuned television channel.

15. The television receiver as set forth in claim 9, wherein the transfer function comprises an all-pass fractional transfer function.

16. The television receiver as set forth in claim 9, wherein the transfer function comprises a real number in the numerator and a complex number in the denominator.

17. The television receiver as set forth in claim 9, wherein the Nyquist slope filter comprises inverters, such that a transfer function for the Nyquist slope filter comprises terms of the numerator with the same sign.

18. The television receiver as set forth in claim 9, wherein the low pass filter comprises a low pass filter with a Butterworth response.