TDA8315 View Datasheet(PDF) - Philips Electronics

Part Name

Description

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TDA8315

Integrated NTSC decoder and sync processor

Philips Electronics 

Philips Semiconductors

Integrated NTSC decoder

and sync processor

Preliminary specification

TDA8315T

FUNCTIONAL DESCRIPTION

CVBS or Y/C input

The TDA8315T has a video input which can be switched

to CVBS (with internal chrominance bandpass and trap

filters) and to Y/C (without chrominance bandpass and

trap filters). The switching between CVBS and Y/C is

achieved by the DC level of the CHROMA input (pin 15).

Integrated video filters

The circuit contains a chrominance bandpass and trap

circuit. The filters are realised by gyrator circuits that are

automatically tuned by comparing the tuning frequency

with the crystal frequency of the decoder. The

chrominance trap can be switched off by the DC level of

the CHROMA input.

The luminance delay line is also realised by gyrator

circuits.

Colour decoder

The colour decoder contains an alignment-free crystal

oscillator, a colour killer circuit and colour difference

demodulators. The gain of the two colour difference signal

demodulators is identical and the phase angle of the

reference carrier signals is 90°. This phase shift is

achieved internally. It is possible to switch the demodulator

angle to 110° by an internal matrix circuit. The switching is

obtained externally via pin 8.

Synchronization circuit

The sync separator is preceded by a voltage controlled

amplifier which adjusts the sync pulse amplitude to a fixed

level. The sync pulses are then fed to the slicing stage

(separator) which operates at 50% of the amplitude.

The separated sync pulses are fed to the first phase

detector and to the coincidence detector. The coincidence

detector is used to detect whether the line oscillator is

synchronized. The PLL has a very high static steepness,

this ensures that the phase of the picture is independent of

the line frequency. The line oscillator operates at twice the

line frequency.

The oscillator network is internal. Because of the spread of

internal components an automatic adjustment circuit has

been added to the IC.

The circuit compares the oscillator frequency with that of

the crystal oscillator in the colour decoder. This results in

a free-running frequency which deviates less than 2% from

the typical value.

The horizontal output pulse is derived from the horizontal

oscillator via a pulse shaper. The pulse width of the output

pulse is 5.4 µs, the front edge of this pulse coincides with

the front edge of the sync pulse at the input.

The vertical output pulse is generated by a count-down

circuit. The pulse width is approximately 380 µs. Both the

horizontal and vertical pulses will always be available at

the outputs even when no input signal is available.

September 1994

5

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