TDA4504 데이터 시트보기 (PDF) - Philips Electronics
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TDA4504 Datasheet PDF : 26 Pages
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Philips Semiconductors
Small signal combination for multistandard colour TV
Product specification
TDA4504B
AGC circuit
For signals employing negative modulation the AGC detector operates on peak sync level but upon peak white content
with those having positive modulation. Selection is facilitated by the system switch (pin 32):
pin 32
pin 32
HIGH/open:
LOW:
The AGC detector currents are:
charge
discharge
positive modulation
1 µA
3 mA
positive modulation
negative modulation
negative modulation
55 µA
1.5 mA
With a 6.8 µF AGC capacitor, the video tilt will be < 10% for positively modulated signals and < 2% for negative
modulation.
To obtain a rapid AGC action when executing a search tuning operation with the circuit set for peak white AGC, the
charge current is held at 55 µA until the detection of a transmitted signal.
The transmitter identification
A mute signal is generated to disable the audio preamplifier of an audio demodulator during the absence of a
transmission signal. When the video switch is in the internal mode, the identification of a transmitted signal is derived
from the coincidence detector.
In the external mode the IF part of the circuit has its own identification system. The system relies upon the detection of
sync. pulses on the incoming IF signal. The separated horizontal sync pulse charges the capacitor on pin 25 which drives
the mute output (pin 14).
The connection of a 1 MΩ resistor between pin 25 and VCC results in the mute information being overruled by the
50/60 Hz information derived from the internal vertical divider section
(see 50/60 Hz truth table).
MUTE Truth Table:
Input signal
Pins 9 and 10
pin 25
pin 28
pin 18
pin 14
50 Hz 60 Hz none 50/60 Hz
9.5 V
50 Hz
LOW
12 V
9.5 V
60 Hz
LOW
9V
0.3 V
none
LOW/
HIGH
0.3 V
9.5 V
50 Hz
HIGH
12 V
50/60 Hz
9.5 V
60 Hz
HIGH
9V
50/60 Hz
9.5 V
none
HIGH
12 V
none
0.3 V
50/60 Hz
HIGH
0.3 V
February 1992
7
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