TDA3567 Philips Semiconductors, TDA3567 Datasheet - Page 4

• Manufacturer Part Number: TDA3567
• Description: NTSC decoder
• Manufacturer: Philips Semiconductors

Philips Semiconductors
FUNCTIONAL DESCRIPTION
Luminance amplifier
The luminance amplifier is voltage driven and requires an input signal of 450 mV peak-to-peak
line must be connected between the i.f. amplifier and the decoder. The input signal must be a.c. coupled to the input pin 8.
The black level clamp circuit of the RGB amplifiers uses the coupling capacitor as a storage capacitor. After clamping
the signal is fed to a peaking stage. The RC network connected to pin 13 is used to define the amount of overshoot.
The peaking stage is followed by a contrast control stage. The control voltage has to be supplied to pin 6. The control
voltage range is nominally 17 to
Chrominance amplifier
The chrominance amplifier has an asymmetrical input. The input signal at pin 3 must be a.c. coupled, and must have an
amplitude of 550 mV peak-to-peak. The gain control stage has a control range in excess of 30 dB, the maximum input
signal should not exceed 1,1 V peak-to-peak, otherwise clipping of the input signal will occur. From the gain control stage
the chrominance signal is fed to the saturation and contrast control stages. Chrominance and luminance control stages
are directly coupled to obtain good tracking. The saturation is linearly controlled via pin 5. The control voltage range is
2 V to 4 V. The impedance is high and the saturation control range is in excess of 50 dB. The burst signal is not affected
by contrast or saturation control. After the amplification and control stages the chrominance signal is internally fed to the
(R-Y) and (B-Y) demodulators, burst phase and a.c.c. detectors.
Oscillator and a.c.c. circuit
The 3,58 MHz reference oscillator operates at the subcarrier frequency. The crystal must be connected between pin 16
and ground. The oscillator does not require adjustment due to the small spreads of the IC. The free running frequency
of the oscillator can be checked by connecting the saturation control (pin 5) to the positive supply line. Then the loop is
opened, so that the frequency can be measured. The oscillator has an internal gain limiting stage which controls the gain
to unity, so that internal signals are sinusoidal. This prevents the generation of higher harmonics of the subcarrier signals.
The burst signal is compared to a 0 reference signal by the burst amplitude detector and is then amplified and fed to a
peak detector for a.c.c. and to a sample and hold circuit which drives the colour killer circuit. The reference signal for the
burst phase detector is provided by the 90 phase shifted signal. An RC network is used to obtain the required catching
range and noise immunity for the output voltage of the burst phase detector.
The hue control is obtained by mixing oscillator signals with a phase of 0 and 90 before they are fed to the (R-Y) and
(B-Y) demodulators. The 90 phase shifted signal is provided by a miller integrator (biased by pin 18). As the hue control
is independent of the PLL, the control will react without time delay on the control voltage changes.
Demodulator circuits
The demodulators are driven by the amplified and controlled chrominance signals, the reference signals are obtained
from the hue control circuit. In nominal hue control position the phase angle of (R-Y) reference signal is 0 , the phase
angle of the (B-Y) reference signal is 90 .
For flesh tone corrections the demodulated (R-Y) signal is matrixed with the demodulated (B-Y) signal according to the
following equations:
(1) Signal with negative going sync; amplitude includes sync pulse amplitude.
June 1986
R Y
G Y
B Y
NTSC decoder
–
–
–
matrixed
matrixed
matrixed
=
=
=
1 61 R Y
0 43 R Y
B Y
–
IN
–
–
IN
IN
–
–
3 dB. The linear curve of the contrast control voltage is shown in Fig.2.
0
0
42 B Y
11 B Y
–
–
IN
IN
4
(1)
The luminance delay
Product specification
TDA3567