TELEFUNKEN Semiconductors

TDA4481-D

Rev. A1: 23.02.1995

2 (10)

Pin Configuration

Pin

Function

1–2

Picture-IF-carrier input

3

SCART-switch

4

AGC storage capacitor

5

SCART-AF input

6

Standard switch

7

AF output (controlled)

8

Volume control voltage

9

SCART-AF output

10

VC0 tank circuit

Pin

Function

11

Ground

12–13

FM demod. circuit 5.5 MHz

14

FM deemphasis capacitor

15

Intercarrier output 5.5 MHz

16

Supply voltage

17

Intercarrier input 5.5 MHz

and muting

18–19

Sound-IF-carrier input

20

not connected

Description

This circuit configuration permits high-quality processing

of audio carriers for all standards, providing separate inputs

for the video and audio carriers. The audio carrier signal

(FM or AM) is passed to two multiplying mixer

arrangements via a 3-stage variable wide-band amplifier

with levelled output signals. One mixer demodulates AM

and generates the gain control signal. The second mixer

operates as an intercarrier demodulator and supplies the

intermediate AF carrier.

The video carrier signal required to form the intercarrier is

decoupled in a prelimited and selected form from the

demodulator tank of the intermediate video frequency

circuit (TDA 4453 or TDA 4439) and led to the intercarrier

mixer via a limiting amplifier. By virtue of the system, the

Nyquist range of the IF input filter in the video channel

affects the attainable AF signal-to-noise ratio.

The audio FM IF carrier reaches a quadrature demodulator

via an interconnected IF-filter and subsequent limiting

amplifier. The resulting AF signal is led via a low-pass

amplifier with increased level and the AF standard switch

to the SCART switch. It is available at both AF outputs,

Pin 14 is provided to connect a de-emphasis capacitor

(10 nF for 50

ms). The de-emphasis is effective for both AF

outputs during FM operation, but deactivated for AM

operation.

A frequency converter is inserted to mix the different

possible sound frequency standards (4.5, 6.0, 6.5 MHz)

into a uniform intermediate audio frequency, e.g. 5.5 MHz.

The VCO frequency (pin 10) can be controlled from the

unlevelled AF output at pin 9 or the de-emphasis

connection at pin 14.

The intercarrier and converter circuits as well as the FM

demodulator are deactivated during AM modulation. FM

muting is also possible if a switching voltage is applied to

pin 17.

All switching functions (standard, SCART, mute) can take

place with TTL-equivalent level.