Philips 7629 Service Manual page 67

Once the signal source is selected, a chroma filter calibration is performed. The
received color burst sub-carrier frequency is used for this. Correspondingly, the chroma
band pass filter for PAL/NTSC processing or the cloche filter for SECAM processing is
switched on. The selected luminance (Y) signal is supplied to the horizontal and vertical
synchronization processing circuit and to the luminance processing circuit. In the
luminance-processing block, the luminance signal goes to the chroma trap filter. This
trap is switched "on" or "off" depending on the color burst detection of the chroma
calibration circuit.
The group delay correction part can be switched between the BG and a flat group delay
characteristic. This has the advantage that in multi-standard receivers no compromise
has to be made for the choice of the SAW filter.
Video demodulation
The color decoder circuit detects whether the signal is a PAL, NTSC or SECAM signal.
The result is made known to the auto system manager. The PAL/NTSC decoder has an
internal clock generator, which is stabilized to the required frequency by using the 12
MHz clock signal from the reference oscillator of the microcontroller / teletext decoder.
The base-band delay line is used to obtain a good suppression of cross color effects.
The Y signal and the delay line outputs U and V are applied to the luminance / chroma
signal processing part of the TV processor.
Luminance / Chrominance signal processing
The output of the YUV separator is fed to the internal YUV switch, which switches
between the output of the YUV separator or the external YUV (for DVD or PIP) on pins
51-53. Pin 50 is the input for the insertion control signal called 'FBL-1'. When this signal
level becomes higher than 0.9 V (but less than 3 V), the RGB signals at pins 51, 52 and
53 are inserted into the picture by using the internal switches.
Also some picture improvement features are implemented in this part: