TDA3592A 데이터 시트보기 (PDF) - Philips Electronics

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TDA3592A

SECAM-PAL transcoder

Philips Electronics 

Philips Semiconductors

SECAM-PAL transcoder

Product specification

TDA3592A

The two colour difference signals are combined again after clamping and then applied to the modulator via de-emphasis,

blanking and reinsertion circuits. The ratio of (R-Y) to (B-Y) at the de-emphasis output (pin 20) is 1,78.

Modulation

A burst signal is reinserted into the combined SECAM signal at the input to the PAL modulator. At this input the phase

relationship for magenta colour is +(R-Y) and −(B-Y). The modulation carriers for the (R-Y) and (B-Y) signals are 90° out

of phase; for a magenta colour the modulated (R-Y) component has the same phase position as the (R-Y) burst. The

(B-Y) burst is modulated 180° out of phase with respect to the (B-Y) component of a magenta-coloured input signal.

Identification SECAM/SECAM

Identification of the SECAM signal is performed using the fact that only SECAM signals have a line-to-line difference in

voltage level. The identification circuit compares the phase of the demodulated voltage difference waveform with the

phase of the flip-flop output. If the phase relationship is not correct, the flip-flop is reset by an extra pulse from the flip-flop

trigger generator. For horizontal identification the phase comparison is performed during the period of pulse ‘B’ (see

Fig.2). When vertical identification is selected, the comparison is performed only during the horizontal scan of the vertical

blanking. The SECAM identification circuits operate when selected by the voltage on pin 4; this may be horizontal, vertical

or combined horizontal and vertical identification, depending on the switching arrangements of pin 4.

These are as follows:

• Horizontal identification preset when V4-1 < 2,9 V;

• Vertical identification preset when V4-1 > 4,1 V;

• Horizontal/vertical combination when sandcastle pulse is present on pin 4.

Information obtained from the identification detector is also used for colour killing and, if required, for switching to PAL.

January 1988

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