TDA8501 Datasheet, PDF (7/30 Pages) NXP Semiconductors – PAL/NTSC encoder

Philips Semiconductors
PAL/NTSC encoder
(1) frequency response.
(2) group delay.
Fig.3 Low pass filter response for colour
difference signals (PAL mode).
(1) frequency response.
(2) group delay.
Fig.4 Low pass filter response for colour
difference signals (NTSC mode).
April 1993
Preliminary specification
TDA8501
Low pass filters
The −3dB nominal frequency response level of the low
pass filters are different in PAL and NTSC modes.
PAL mode: bandwidth = 1.35 MHz nominal (see Fig.3).
NTSC mode: bandwidth = 1.1 MHz nominal (see Fig.4).
The signal outputs of the low pass filters are connected to
the signal inputs of the U and V modulators.
U AND V MODULATORS
Two four-quadrant multipliers are used for quadrature
amplitude modulation of the U and V signals. The level of
harmonics produced by the modulated signals are
minimal, because of real multiplication with sinewave
carriers.
The unbalance of the modulators is minimized by means
of a control loop and two external capacitors, pin 6 for the
U modulator and pin 12 for the V modulator. The timing of
the control loop is triggered by the H/2 pulse, so that during
one sync period the U control is active and during the next
sync period the V control is active. In this way, when U and
V are both zero, the suppressed carrier is guaranteed to be
at a low level.
The internal oscillator circuit generates two sinewave
carriers (0 degree and 90 degree). The '0 degree' (0)
carrier is connected to the U modulator and the '90 degree'
(1) carrier is connected to the V modulator.
PAL mode:
• switched sequentially by the H/2 pulse, the V signal is
modulated alternately with the direct and inverse carrier.
• the internal H/2 pulse can be forced into a specific phase
by means of an external pulse connected to pin 4 (H/2).
Forcing is active at HIGH level. If not used pin 4 can be
left open-circuit or connected to ground. If pin 4 is left
open, the internally generated H/2 pulse (output) is
connected to this pin.
NTSC mode:
• alternation of the V modulation is not allowed. If pin 4 is
not used for set-up control (see Y +SYNC, CVBS and
Chrominance outputs), it can be left open-circuit or
connected to ground.
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