TDA4472-M

Preliminary Information

TELEFUNKEN Semiconductors

Rev. A2, 15-Oct-96

3 (14)

Circuit Description

Vision IF Amplifier

The video IF signal (VIF) is fed through a SAW filter to

the differential input (Pin 6-7) of the VIF amplifier. This

amplifier consists of three AC-coupled amplifier stages.

Each differential amplifier is gain controlled by the auto-

matic gain control (VIF-AGC). The output signal of the

VIF amplifier is applied to the FPLL carrier generation

and the video demodulator.

Tuner-and VIF-AGC

At Pin 8, the VIF-AGC charges/discharges the AGC

capacitor to generate a control voltage for setting the gain

of the VIF amplifier and tuner in order to keep the video

output signal at a constant level. Therefore, in the case of

all negative modulated signals (e.g., B/G standard) the

sync. level of the demodulated video signal is the

criterion for a fast charge/discharge of the AGC capacitor.

The control voltage (AGC voltage at Pin 8) is transferred

to an internal control signal, and is fed to the tuner AGC

to generate the tuner AGC current at Pin 11 (open

collector output). The take over point of the tuner AGC

can be adjusted at Pin 10 by a potentiometer or an external

dc voltage (from interface circuit or microprocessor).

FPLL, VCO and AFC

The FPLL circuit (frequency phase locked loop) consists

of a frequency and phase detector to generate the control

voltage for the VCO tuning. In the locked mode, the VCO

is controlled by the phase detector and in unlocked mode,

the frequency detector is superimposed. The VCO

operates with an external resonance circuit (L and C par-

allel) and is controlled by internal varicaps. The VCO

control voltage is also converted to a current and repre-

sents the AFC output signal at Pin 22.

A practicable VCO alignment of the external coil is the

adjustment to zero AFC output current at Pin 22. At center

frequency the AFC output current is equal to zero.

The optional potentiometer at Pin 26 allows an offset

compensation of the VCO phase for improved sound

quality (fine adjustment). Without a potentiometer (open

circuit at Pin 26), this offset compensation is not active.

The oscillator signal passes a phase shifter and supplies

the in-phase signal (0

°) and the quadrature signal (90°)of

the generated picture carrier.

Video Demodulation and Amplifier

The video IF signal, which is applied from the gain

controlled IF amplifier, is multiplied with the inphase

component of the VCO signal. The video demodulator is

designed for low distortion and large bandwidth. The

demodulator output signal passes an integrated low pass

filter for attenuation of the residual vision carrier and is

fed to the video amplifier. The video amplifier is realized

by an operational amplifier with internal feedback and

8 MHz bandwidth (–3 dB). An additional noise clipping

is provided. The video signal is fed to VIF-AGC and to the

video output buffer. This amplifier with a 6 dB gain offers

easy adaption of the sound trap. For nominal video IF

Sound IF Amplifier and SIF-AGC

The SIF amplifier is nearly identical with the 3-stage VIF

amplifier. Only the first amplifier stage exists twice and

is switchable by a control voltage at Pin 3. Therefore with

a minimal external expense it is possible to switch

between two different SAW filters. Both SIF inputs

features excellent cross-talk attenuation and an input

impedance which is independent from the switching

condition.

The SIF-AGC is related to the average level of FM-carrier

and controls the SIF amplifier to provide a constant SIF

signal to the QPS mixer.

Quasi-Parallel-Sound (QPS) Mixer

The QPS mixer is realized by a multiplier. The SIF signal

(FM or NICAM carrier) is converted to the intercarrier

frequency by the regenerated picture carrier (quadrature

signal) which is provided from the VCO. The intercarrier

signal is fed via an output amplifier to Pin 24.

AFC Switch

The AFC output signal at Pin 22 can be controlled by a

switching voltage at Pin 19. It is possible to switch off the

AFC.

VCR Mode

For the VCR mode in a TV set (external video source

selected), it is recommendable to switch off the IF circuit.

With an external switching voltage at Pin 6 or 7, the IF

amplifiers are switched off and all signal output levels at

Pins 12 and 24 are according to the internal dc voltage.

Internal Voltage Stabilizer

The internal bandgap reference ensures constant perfor-

mance independent of supply voltage and temperature.