November 1987

4

Philips Semiconductors

Product specification

Television IF amplifier and demodulator

TDA8340

TDA8341

PINNING

FUNCTIONAL DESCRIPTION

IF amplifier

This is a 3-stage, gain-controlled IF amplifier with a wide dynamic range. On-chip capacitors in the d.c. feedback loop of

the amplifier maintain stability at maximum gain. Internal stabilization of the supply voltage ensures the desired sensitivity

and gain control range over the whole supply voltage range and also gives very good power supply ripple rejection in this

part of the circuit.

Demodulator

The redesigned IF demodulator is a quasi-synchronous circuit that employs passive carrier regeneration and logarithmic

clamping to give improved signal handling. The demodulator input is a.c. coupled to the IF amplifier to reduce d.c. offsets

and thus minimize residual IF carrier in the output signal.

Video amplifier

The linearity and bandwidth of the video amplifier are sufficient to meet all wide band requirements, e.g. for teletext

transmissions. Second harmonics of the IF carrier are effectively reduced by a Sallen-Key low pass interstage filter

between the demodulator output and the video amplifier input. An integrated filter in the noise inverter reduces the

sensitivity of the video amplifier for high sound carriers.

White spot protection comprises a white spot clamp system combined with a delayed-action inverter which is also highly

resistant to high sound carriers.

Note. To prevent radiated video output at the input pins, connect a 6,8

µH inductor in series with pin 12 and fit as close

as possible to the IC body. Use short leads.

AGC detector

A Bessel low-pass filter between the video output and the AGC detector improves the detector function in the presence

of high sound carriers. No ‘hang-up’ occurs in the detector after pin 14 has been short-circuited to ground (VCR switch

operated). The detector also generates the sample-and-hold pulse for the AFC system.

1 and 16

Balanced IF inputs

2 and 15

IF amplifier decoupling

3

Tuner AGC starting point adjustment

4

Tuner AGC output

5

AFC output

6

AFC on/off switch and sample-and-hold capacitor

7 and 10

Reference carrier

π/2 rad. phase shift

8 and 9

IF picture carrier passive regeneration

11

12

Video output

13

14

IF AGC capacitor and VCR switch