Digital demodulator with a unit for correcting over modulation and preventing black reversing

• US 5,293,247 A
• Filed: 03/10/1993
• Issued: 03/08/1994
• Est. Priority Date: 03/26/1992
• Status: Expired due to Term

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Ganse, Shigeru
• Primary Examiner(s): Hajec, Donald
• Assistant Examiner(s): WAMSLEY, PATRICK G
• Application Number:
  US08/029,066
• Time in Patent Office: 363 Days
• Field of Search: 360/65, 360/29, 360/32, 360/46, 358/328, 358/23, 358/330, 358/323, 358/133, 358/335, 358/327, 358/340, 358/336, 358/36, 358/167
• US Class Current: 386/269
• CPC Class Codes: H03D 2200/0021 Frequency multipliers
• CPC Class Codes: H03D 2200/005 Analog to digital conversion
• CPC Class Codes: H03D 2200/0054 Digital filters
• CPC Class Codes: H03D 3/006 by sampling the oscillations and further processing the samples, e.g. by computing techniques H03D3/007 takes precedence
• CPC Class Codes: H03D 3/008 Compensating DC offsets
• CPC Class Codes: H04N 5/92 Transformation of the television signal for recording, e.g. modulation, frequency changing; Inverse transformation for playback
• CPC Class Codes: H04N 5/93 Regeneration of the television signal or of selected parts thereof

Abstract

A digital demodulator includes a reproducing head for reproducing an analog video signal from a recording medium, an analog to digital converter for converting the analog video signal applied from the reproducing head into a digital signal, a Hilbert transform circuit for transforming the digital signal into signals whose phases are shifted by first and second angles from the digital signal, respectively, a frequency detector for detecting a frequency of the transformed signals, a first coefficient circuit for weighting an output signal of the frequency detector, a second coefficient circuit for weighting the transformed signals, a multiplier for multiplying output signals of the first and second coefficient circuits together, an equalizer for correcting a frequency characteristic of the transformed signals, and a demodulator for demodulating an output signal of the equalizer, wherein the frequency characteristic of the equalizer is corrected in accordance with an output of the multiplier.

Claims

1. A digital demodulator comprising:

a reproducing head for reproducing an analog video signal from a recording medium;

an analog to digital converter for converting the analog video signal from said reproducing head into a digital signal;

a Hilbert transform circuit for transforming the digital signal into transformed signals whose phases are shifted by first and second angles from a phase of the digital signal, respectively;

a frequency detector for detecting a frequency of the transformed signals;

first coefficient calculation means for producing a weighting coefficient from an output signal of said frequency detector;

second coefficient calculation means for producing a weighting coefficient from the transformed signals;

a multiplier for multiplying together the weighting coefficients from said first and second coefficient calculation means and producing a correction signal;

an equalizer receiving said correction signal and said transformed signals for correcting a frequency characteristic of the transformed signals in response to said correction signal; and

a demodulator for demodulating an output signal of said equalizer, wherein the frequency characteristic of said equalizer is corrected in accordance with said correction signal from said multiplier.

2. A digital demodulator according of claim 1, wherein each of said first and second coefficient calculation means comprises a read only memory table.

3. A digital demodulator according to claim 1, wherein said Hilbert transform circuit transforms the digital signal into complex signals and said first and second angles are 0°

and 90°

, respectively.

4. A digital demodulator according to claim 3, wherein said equalizer is formed of a plurality of delay circuits, adders and amplifiers.

5. A digital demodulator according to claim 4, wherein said equalizer makes both a higher frequency band and a lower frequency band of the reproduced video signal substantially half of an intermediate frequency band.