U4935B Datasheet, PDF (9/16 Pages) TEMIC Semiconductors – SECAM Decoder

U4935B
Demodulator
The bell filter delivers the C signal via a limiter amplifier
to the demodulator. The demodulator is of a phase-locked
loop (PLL) type VCO and a phase-emitter coupled
multivibrator with the limiter output and is fed back to the
VCO. The free-running frequency is adjusted by charging
or discharging the capacitor at Pin 8 during the vertical
blanking and is held during scanning.
Therefore, the IC needs no adjustment to enable constant
operation
The low-frequency de-emphasis is matched to the PLL
and is controlled by the tuning voltage of the PLL.
The capacitor, C8, should be connected as close as
possible to the ground pin of the package. If this is not
ensured, a black-level error for both channels may result.
Bell-filter
output
Limiter
VBLK pulse
LPF
VCO
PLL
De–
emphasis
to H,
V blanking
9611721
Tuning
8 PLL
ref
C₈
Figure 18. Block diagram of the demodulator
TELEFUNKEN Semiconductors
9 (16)
Rev. A1, 28-Jan-97
Preliminary Information