January 1988

7

Philips Semiconductors

Product specification

SECAM-PAL transcoder

TDA3592A

Coupling of identification systems

Coupling of a TDA3592A and a PAL decoder can be performed to obtain an optimum identification system. The system

operates using the functions of pins 13, 6 and 7: the voltage level at pin 13 is controlled by the PAL/PAL detection of the

PAL decoder; and the voltage level at pins 6 and 7 are functions of SECAM/SECAM detection in the TDA3592A.

The circuit action is as follows and is summarized in Table 1.

Table 1

System operating modes

System priorities

When TDA3592A pin 13 is connected to the PAL/PAL output of a PAL decoder, the system will give PAL priority in signal

identification. Connecting TDA3592A pin 13 to ground will give SECAM priority.

Luminance and chrominance signal paths

The signal input at pin 16 is clamped by a circuit which detects the top of the luminance signal sync pulse. This clamp,

the luminance signal path to pin 15 and the SECAM signal path to pin 14 remain active when the supply voltage falls to

(typ.) 5 V. At this level of supply voltage the SECAM processing circuits are switched off, giving a reduction in total power

dissipation.

Channel switching

During channel switching pin 6 is taken rapidly to a high voltage (

± 10,2 V), this corresponds

to the SECAM mode of the TDA3592A.

PAL

The high voltage level at pin 6 caused by channel switching is maintained by the TDA3592A

when it recognizes the signal as SECAM (this condition is maintained even if reflected PAL

signals are present). The PAL decoder recognizes the signal as PAL and takes pin 13 of

TDA3592A to a voltage greater than 1,7 V. The TDA3592A is now held in the SECAM

condition by an internal current source at pin 6.

SECAM

The initial high voltage level (

+ 10,2 V) at pin 6 caused by channel switching sets the

TDA3592A in the SECAM mode and during this time the PAL decoder detects a PAL signal.

This causes a voltage at pin 13 of

< 1,1 V which prevents the internal current source of

TDA3592A maintaining the high voltage level of pin 6 which, in turn, allows the TDA3592A to

detect SECAM. The initiation of SECAM detection is delayed by the action of the external

circuit at pins 6 and 7 and commences as pin 6 approaches 7,0 V. The SECAM signals are

converted by TDA3592A to PAL signals at pin 14, which results in the PAL decoder switching

to the PAL mode (the TDA3592A remains in the SECAM mode).

Black-and-white

The TDA3592A is initially set in the SECAM mode as previously described. The PAL decoder

detects PAL and the TDA3592A detects SECAM which results in a system operation in the

colour-killing mode.

TDA3592A

PAL DECODER MODE

SYSTEM OPERATING MODE

SECAM

PAL

SECAM

SECAM

PAL

condition not used

SECAM

PAL

PAL

SECAM

PAL

black-and-white