Video

Amplifier

Band Gap

Voltage Reference

IF Amplifier

AFC

AGC

Reference

Amplifier

20

19

22

18

14

12

13

21

11

17

8

9

3

2

5

6

124

23

7

4

TDA8222

D.C. Volume

Control

6dB

15

16

10

FM

Discri

Limiter

LP Filter

Mute

Tuner

AGC

White and

Black Noise Inverter

6dB

BLOCK DIAGRAM

FUNCTIONAL DESCRIPTION

General

The IC consists of the following parts (see block

diagram):

- Three stages gain controlled wide band amplifier

- Quasi-synchronous demodulator

- Video amplifier with white and black noise in-

verter

- AGC circuit which operates on top sync level

- Analog AFC circuit

- FM discriminator

- Mute function

- Video and audio switches

- DC volume control

IF Amplifier

It consists of three cascaded AC coupled differen-

tial gain stages. The gain of each amplifier is con-

trolled by the AGC voltage. The global AGC range

is more than 60dB. Thanks to the internal AC

coupling no DC feedback is required.

Demodulation

It is a quasi-synchronous type with passive carrier

regeneration done by an external tuned circuit, and

a limiter amplifier.

Video Amplifier

the output with a good phase and amplitude fre-

quency response.

White and Black Noise Inverter

A fixed 3.2V level is inserted when a white spot

above 4.5V (measured on the video output Pin 18)

happens, this prevents from very noisy signal on

the screen.

A fixed 2.5V level is inserted when a black spot

below 1.3V happens, this to avoid synchronization

on parasitic signals.

AGC Circuit

The AGC detector operates on top sync level, an

external capacitor on Pin 24 controls the time con-

stant.

The voltage on this capacitor is converted into a

current to control the amplifier stage.

TDA8222

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