THOMSON VP2750 Technical Manual page 97

SECAM CHROMINANCE PROCESSING DURING RECORDING
The SECAM chrominance processing of R6000 Series video recorders is handled by IC100, a
specialised integrated circuit.
The composite video signal, output from Pin 3 of IX001, is applied to Pin 15 of IC100. The
chrominance component of this signal is taken by a 4.4-MHz band pass filter.
The SECAM chroma, thus selected, is sent to a bell filter with central frequency 4.28 MHz.
This filter shapes the chroma signal to obtain a constant level whatever the signal frequency
deviation. The bell filter consists of LC004 and CC019.
The chroma signal is sent to a limiter stage. This circuit clips the signal, thus transforming the
input sinusoidal signal into a square signal. This creates good conditions for entering the four-
way divider.
At the divider output, the SECAM chroma signal is transposed to 1.07 MHz. The band pass
filter, with a central frequency of 1.1 MHz, isolates the fundamental of the square signal, and
thereby returns the chroma signal to sinusoidal form.
The signal is sent to an anti-bell filter with central frequency 1.07 MHz, consisting of LC001 and
CC005.
The SECAM chrominance signal is output at 11 of IC100 via a mute circuit.
The chroma signal is then mixed with the Y FM signal via TC015, IC101, and TC009.
CHROMA ERASURE
Line erasure is performed by the line synchronisation time signals at 27 of IC100.
Frame erasure is performed by a VCO locked by the frame sync present at 27 of IC100.
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