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SAA7191B

Digital multistandard colour decoder, square pixel (DMSD-SQP).

Philips Electronics 

Philips Semiconductors

Digital Multistandard Colour Decoder,

Square Pixel (DMSD-SQP)

7 FUNCTIONAL DESCRIPTION

7.1 Chrominance processor

The 8-bit chrominance input signal (CVBS or chrominance

format) passes a bandpass filter to eliminate DC

components and to decimate the sample rate before it is

fed to the two multipliers (quadrature demodulator), Fig.3.

Two subcarrier signals from a local oscillator (0 to 90

degree) are fed to the multiplicator inputs of the multipliers.

The multipliers operate as a quadrature demodulator for all

PAL and NTSC signals; it operates as a frequency

down-mixer for SECAM signals.

The two multiplier output signals are converted to a serial

data stream and applied to three low-pass filter stages,

then to a gain controlled amplifier. A final multiplexed

low-pass filter achieves, together with the preceding

stages, the required bandwidth performance. The signals,

originated from PAL and NTSC, are applied to a

comb-filter. The signals, originated from SECAM, are fed

through a Cloche filter (0 Hz centre frequency), a phase

demodulator and a differentiator to obtain

frequency-demodulated colour-difference signals.The

SECAM signals are fed after de-emphasis to a cross-over

switch, to provide the both serial-transmitted

colour-difference signals. These signals are fed finally to

the output formatter stages and to the output interface.

Product specification

SAA7191B

August 1996

8

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