TDA3566 Philips Semiconductors, TDA3566 Datasheet - Page 6

• Manufacturer Part Number: TDA3566
• Description: PAL/NTSC decoder
• Manufacturer: Philips Semiconductors

Philips Semiconductors
The time constant of the saturation
control (pin 5) provides a delayed
switch-on after killing. Adjustment of
the oscillator is achieved by variation
of the burst phase detector load
resistance between pins 24 and 25
(see Fig.8).
With this application the trimmer
capacitor in series with the 8.8 MHz
crystal (pin 26) can be replaced by a
fixed value capacitor to compensate
for unbalance of the phase detector.
Demodulator
The (R Y) and (B Y) demodulators
are driven by the colour difference
signals from the delay-line matrix
circuit and the reference signals from
the 8.8 MHz divider circuit. The (R Y)
reference signal is fed via the
PAL-switch. The output signals are
fed to the R and B matrix circuits and
to the (G Y) matrix to provide the
(G Y) signal which is applied to the
G-matrix. The demodulation circuits
are killed and blanked by by-passing
the input signals.
NTSC mode
The NTSC mode is switched on when
the voltage at the burst phase
detector outputs (pins 24 and 25) is
adjusted below 9 V.
To ensure reliable application the
phase detector load resistors are
external. When the TDA3566A is
used only for PAL these two 33 k
resistors must be connected to +12 V
(see Fig.8).
For PAL/NTSC application the value
of each resistor must be reduced to
20 k (with a tolerance of 1%) and
connected to the slider of a
potentiometer (see Fig.9). The
switching transistor brings the voltage
at pins 24 and 25 below 9 V which
switches the circuit tot the NTSC
mode.
February 1994
PAL/NTSC decoder
The position of the PAL flip-flop
ensures that the correct phase of the
(R Y) reference signal is supplied to
the (R Y) demodulator.
The drive to the H/2 detector is now
provided by the (B Y) reference
signal. In the PAL mode it is driven by
the (R Y) reference signal. Hue
control is realized by changing the
phase of the reference drive to the
burst phase detector.
This is achieved by varying the
voltage at pins 24 and 25 between
7.0 V and 8.5 V, nominal position
7.65 V. The hue control characteristic
is shown in Fig.6.
RGB matrix and amplifiers
The three matrix and amplifier circuits
are identical and only one circuit will
be described.
The luminance and the colour
difference signals are added in the
matrix circuit to obtain the colour
signal, which is then fed to the
contrast control stage.
The contrast control voltage is
supplied to pin 6 (high-input
impedance). The control range is
+5 dB to 11.5 dB nominal. The
relationship between the control
voltage and the gain is linear (see
Fig.3).
During the 3-line period after blanking
a pulse is inserted at the output of the
contrast control stage. The amplitude
of this pulse is varied by a control
voltage at pin 11. This applies a
variable offset to the normal black
level, thus providing brightness
control.
The brightness control range is 1 V to
3.6 V. While this offset level is
present, the black-current input
impedance (pin 18) is high and the
internal clamp circuit is activated. The
clamp circuit then compares the
6
reference voltage at pin 19 with the
voltage developed across the
external resistor network R
R
picture tube beam current.
The output of the comparator is
stored in capacitors connected from
pins 10, 20 and 21 to ground which
controls the black level at the output.
The reference voltage is composed
by the resistor divider network and the
leakage current of the picture tube
into this bleeder. During vertical
blanking, this voltage is stored in the
capacitor connected to pin 19, which
ensures that the leakage current of
the CRT does not influence the black
current measurement.
The RGB output signals can never
exceed a level of 10.6 V. When the
signal tends to exceed this level the
output signal is clipped. The black
level at the outputs (pins 13, 15 and
17) will be approximately 3 V. This
level depends on the spread of the
guns of the picture tube. If a beam
current stabilizer is not used it is
possible to stabilize the black levels at
the outputs, which in this application
must be connected to the black
current measuring input (pin 18) via a
resistor network.
B
(pin 18) which is provided by
Product specification
TDA3566A
A
and