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TEA2028B

COLOR TV SCANNING AND POWER SUPPLY PROCESSOR

STMicroelectronics 

TEA2028B

GENERAL DESCRIPTION

Introduction

This integrated circuit uses I2L bipolar technology

and combines analog signal processing with digital

processing.

Timing signals are obtained from a voltage-control-

led oscillator (VCO) operating at 500kHz by means

of a cheap ceramic resonator. This avoids the

frequency adjustment normally required with line

and frame oscillators.

A chain of dividers and appropriate logic circuitry

produce very accurately defined sampling pulses

and the necessary timing signals.

The principal functions implemented are :

- Horizontal scanning processor.

- Frame scanning processor :

B Class Power stage using an external power

amplifier with fly back generator such as the

TDA8170.

- Secondary switch mode power regulation.

- The SMPS output synchronize a primary I.C.

TEA2261 at the mains part.

- This concept allows ACTIVE STANDBY facilities.

- Line and frame synchronization separation.

- Dual phase-locked loop horizontal scanning.

- High performance frame and line synchronization

with interlacing control.

- Video identification circuit.

- Super sandcastle.

- Automatic 50-60Hz standard identification.

- VCR input for PLL time constant and frame syn-

chro switching.

- Frame saw-tooth generator.

- Frame blanking output.

- Switching mode regulated power supply compris-

ing error amplifier and phase modulator.

- Security circuit and start-up processor.

- 500kHz VCO.

The circuit is supplied in a 28 pin DIP case.

VCC = 12V.

Synchronization Separator

Line synchronization separator is clamped to black

level of input video signal with synchronization

pulse bottom level measurement.

The synchronization pulses are divided centrally

between the black level and the synchronization

pulse bottom level, to improve performance on

video signals in noise conditions.

Frame Synchronization

Time constant of Frame Separator can be adjusted

by adding a capacitor pin 20.

The frame timing identification logic permits auto-

matic adaptatio to 50 - 60Hz standards or non-in-

terlaced video.

An automatic synchronization window width sys-

tem provides :

- fast frame capture (6.7ms wide window),

- good noise immunity (0.4ms narrow window).

The internal generator starts the discharge of the

saw-tooth generator capacitor so that it is not dis-

turbed by line fly-back effects.

Thanks to the logic control, the beginning of the

charge phase does not depend on any disturbing

effect of the line fly-back.

A 32µs timing is automatically applied on standardi-

zed transmissions, for perfect interlacing.

In VCR mode, the discharge time is controlled by

an internal monostable independent of the line

frequency and gives a direct frame synchroniza-

tion.

Horizontal Scanning

The horizontalscanning frequency is obtainedfrom

the 500kHz VCO.

The circuit uses two phase-locked loops (PLL) :

the first one controls the frequency, the second one

controls the relative phase of the synchronization

and line fly-back signals.

The frequency PLL has two switched time con-

stants to provide :

- capture with a short time constant,

- good noise immunity after capture with a long

time constant.

The output pulse has a constant duration of 29µs

(with C(pin 1) = 3.3nF), independent of VCC and

delay in switching off the scanning transistor.

Video Identification

The horizontal synchronization signal is sampled

by a 2µs pulse within the synchronization pulse.

The signal is integrated by an external capacitor.

The identification function provides three different

levels :

- 0V : no video identification

- 6V : 60Hz video identification

- 12V : 50Hz video identification

This information may be used for timing research

in the case of frequency or voltage synthetizer type

receivers and for audio muting.

Super Sandcastle with 3 levels : burst, line fly-

back, frame blanking

In the event of vertical scanning failure, the frame

blanking level goes high to protect the tube.

Frame blanking time (start with reset of frame

divider) is 21 lines.

VCR Input

This provides for continuous use of the short time

constant of the first phase-locked loop (frequency).

In VCR mode, the frame synchronization window

widens out to a search window and there is no

delay of frame fly-back (direct synchronization).

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