TDA8303 datasheet(2/21 Pages) PHILIPS

2 / 21 page

July 1992

Philips Semiconductors

Preliminary speciﬁcation

Small signal combination IC for black/white TV

TDA8303

TDA8303A

FEATURES

• Video IF amplifier with synchronous demodulator

• Automatic gain control (AGC) detector suitable for

negative modulation

• AGC tuner

• Automatic frequency control (AFC) circuit with

sample-and-hold

• Video preamplifier

• Sound IF amplifier and demodulator

• DC volume control or separate supply for starting the

horizontal oscillator

• Audio preamplifier

• Horizontal synchronization circuit with two control loops

• Vertical synchronization (divider system) and sawtooth

generation with automatic amplitude adjustment for 50

and 60 Hz

• Transmitter identification (mute)

GENERAL DESCRIPTION

The TDA8303/TDA8303A combines all small signal

functions (except the tuner) which are required for a

monochrome television receiver. For a complete black and

white receiver only the output stages for video, sound,

horizontal and vertical deflection and a tuner have to be

added.

The TDA8303 is for applications with npn tuners and the

TDA8303A for pnp tuners.

FUNCTIONAL DESCRIPTION

Video IF ampliﬁer, demodulator and video ampliﬁer

Each of the three AC-coupled IF stages permits the

omission of DC feedback and possesses a control range

in excess of 20 dB. An additional advantage is the

symmetry of the amplifier which results in a less critical

application.

The IF amplifier is followed by a passive synchronous

demodulator providing a regenerated carrier signal. This is

limited by a logarithmic limiter circuit prior to its application

to the demodulator. The limiter has a very low differential

phase shift which results in good differential gain and

phase figures.

The video amplifier also contains a white spot inverter and

a noise clamp which limits interference pulses to a point

below the peak sync level. This circuit is more effective

than a noise inverter and results in an improved picture

stability, with respect to interference.

AFC-circuit

The reference signal for the AFC circuit is obtained from

the demodulator tuned circuit. In this way only one tuned

circuit needs to be applied and only one adjustment has to

be carried out. The disadvantage with this method is that

the frequency spectrum of the signal fed to the detector is

determined by the SAW filter characteristic. This spectrum

is asymmetrical with respect to the picture carrier so that

the AFC output voltage is dependent on the video signal.

To overcome this video frequency dependency of the AFC

output, the demodulator output is followed by a

sample-and-hold circuit which samples during the sync

level of the signal. This means that only the carrier signal

is available to the AFC and it will not be affected by the

video information.

At very weak input signals the drive signal of the AFC

circuit will contain substantial noise. This noise has an

asymmetrical frequency spectrum causing an offset in the

AFC output voltage. This effect can be minimized by

applying a notch in the demodulator tuned circuit. The

sample-and-hold circuit is followed by an amplifier with

high output impedance, therefore the steepness of the of

the AFC control voltage is dependent on the load

impedance.

ORDERING INFORMATION

Note

1. SOT117-1; 1996 December 3.

EXTENDED TYPE

NUMBER

PACKAGE

PINS

PIN POSITION

MATERIAL

CODE

TDA8303

DIL

plastic

SOT117(1)

TDA8303A

DIL

plastic

SOT117(1)

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