February 1992

7

Philips Semiconductors

Product specification

Small signal combination for multistandard colour TV

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):

The AGC detector currents are:

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 M

50/60 Hz information derived from the internal vertical divider section

(see 50/60 Hz truth table).

MUTE Truth Table:

pin 32

HIGH/open:

positive modulation

pin 32

LOW:

negative modulation

positive modulation

negative modulation

charge

1

µA55 µA

discharge

3 mA

1.5 mA

Input signal

Pins 9 and 10

50 Hz

60 Hz

none

50/60 Hz

50/60 Hz

50/60 Hz

none

pin 25

9.5 V

9.5 V

0.3 V

9.5 V

9.5 V

9.5 V

0.3 V

pin 28

50 Hz

60 Hz

none

50 Hz

60 Hz

none

50/60 Hz

pin 18

LOW

LOW

LOW/

HIGH

HIGH

HIGH

HIGH

HIGH

pin 14

12 V

9 V

0.3 V

12 V

9 V

12 V

0.3 V