Television – Image signal processing circuitry specific to television – Chrominance signal demodulator
Reexamination Certificate
1999-02-18
2001-04-10
Hsia, Sherrie (Department: 2614)
Television
Image signal processing circuitry specific to television
Chrominance signal demodulator
C348S639000, C348S507000, C348S727000, C348S640000
Reexamination Certificate
active
06215528
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and to an apparatus for digital multi-standard PAL/NTSC/SECAM color demodulation.
BACKGROUND OF THE INVENTION
The key component of a digital PAL or NTSC color decoder is a quadrature demodulator for these AM modulated signals. For a SECAM color decoder, however, an FM demodulator is required which is conventionally implemented using a Hilbert filter which is followed by a CORDIC processor (coordinate rotation digital computer) and a differentiation stage. EP-A-0 597 160 discloses a corresponding digital stand-alone SECAM decoder. A CORDIC processor is described in more detail in EP-A-0 329 812 and EP-A-0 597 160 and in an article cited therein.
SUMMARY OF THE INVENTION
It would be advantageous if for multi-standard TV or VCR applications a multi-standard digital color demodulator for PAL, NTSC and SECAM TV systems could be implemented on one chip having as much as possible common demodulation processing stages. However, since PAL and NTSC use AM modulation whereas SECAM uses FM modulation with two different carriers for the color information in the composite video signal, a conventional solution for a digital SECAM color demodulator using a Hilbert filter as shown in EP-A-0 597 160 has little commonness to that for a digital PAL and/or NTSC color demodulator using a quadrature mixer. Thus, it seems to be inconvenient to combine both solutions on a multi-standard color demodulator chip for all of the three systems. However, the inventors have found a solution for this problem which allows to have a single common quadrature demodulator or mixer for all three color systems.
Accordingly, it is one object of the invention to disclose a method for digitally demodulating PAL, NTSC and SECAM color signals using at least one common processing stage. It is a further object of the invention to disclose an apparatus which utilises the inventive method.
According to the invention, the Hilbert filter disclosed in EP-A-0 597 160 is replaced by a quadrature mixer operating with a single mixer frequency in the first step of the SECAM color demodulation. For this quadrature mixer the already existing quadrature mixer for the PAL/NTSC demodulation can be used. Thereby for a major part of the color demodulation process a common structure is obtained.
In principle, the inventive method is suited for digital SECAM color signal demodulation, wherein the initial demodulation step is carried out using a quadrature mixer.
In principle the inventive apparatus is suited for digital PAL or NTSC or SECAM color signal demodulation and includes:
a quadrature mixer which outputs the PAL or NTSC color components or in case of SECAM an x and an y signal, wherein in case of SECAM a single mixing frequency is used resulting in a bias effect caused by the non-standard-matching color carrier mixing frequency or frequencies;
a stage, in particular a CORDIC processor, which in case of SECAM calculates the function arctan(y/x);
a subsequent stage in which a differentiation and a clamping is performed on the arctan(y/x) signal, wherein said bias effect is corrected by a corresponding clamping operation and wherein the SECAM color components are obtained through an identification of the U and V lines,
or includes:
a quadrature mixer which outputs the PAL or NTSC color components or in case of SECAM an x and an y signal, wherein in case of SECAM the mixing frequency is switched line-alternately to one of the standard SECAM color carrier frequencies;
a stage, in particular a CORDIC processor, which in case of SECAM calculates the function arctan(y/x);
a subsequent stage in which a differentiation is performed on the arctan(y/x) signal, wherein the SECAM color components are obtained through an identification of the U and V lines.
REFERENCES:
patent: 5136369 (1992-08-01), Bohme
patent: 5635995 (1997-06-01), Strolle
patent: 0329812 (1989-08-01), None
patent: 0486095A1 (1992-05-01), None
patent: 0597160A1 (1994-05-01), None
patent: WO91/12696 (1991-08-01), None
Copy of the European Search Report listing the above-cited references.
European search report dated Jul. 29, 1998.
Erbar Maximilian
Lin Jinan
Deutsche Thomson-Brandt GmbH
Hsia Sherrie
Shedd Robert D.
Tripoli Joseph S.
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