October 1991

4

Philips Semiconductors

Preliminary specification

SECAM decoder

TDA8395

FUNCTIONAL DESCRIPTION

The TDA8395 is a self-calibrating SECAM decoder

designed for use with a baseband delay circuit.

During frame retrace a 4.433619 MHz reference frequency

is used to calibrate the filters and the demodulator. The

reference frequency should be very stable during this

period.

The Cloche filter is a gyrator-capacitor type filter the

resonance frequency of which is controlled during the

calibration period and offset during scan; this ensures the

correct frequency during calibration.

The demodulator is a Phase-Locked Loop (PLL) type

demodulator which uses the frequency reference and the

bandgap reference to force the PLL to the required

demodulation characteristic.

The low frequency de-emphasis is matched to the PLL and

is controlled by the tuning voltage of the PLL.

A digital identification circuit scans the incoming signal for

SECAM (only line-identification is implemented). The

identification circuit needs to communicate with the

TDA8362 to guarantee that the output signal from the

decoder is only available when no PAL signal has been

identified. If a SECAM signal is decoded a request for

colour-on is transmitted to pin 1 (current is sunk). If the

signal request is granted (i.e. pin 1 is HIGH therefore no

PAL) the colour difference outputs (

−(B−Y) and −(R−Y))

from the TDA8362 are high impedance and the output

signals from the TDA8395 are switched ON.

If no SECAM signal is decoded during a two-frame period

the demodulator will be initialized before another attempt

is made also during a two-frame period. The CD outputs

will be blanked or high-impedance depending on the logic

level at pin 1.

A two-level sandcastle pulse generates the required

blanking periods and, also, clocks the digital identification

pulse on the falling edge of the burst gate pulse. To enable

the calibration period to be defined the vertical retrace is

discriminated from the horizontal retrace, this is achieved

by measuring the width of the blanking period.

LIMITING VALUES

In accordance with the Absolute Maximum System (IEC 134)

SYMBOL

PARAMETER

MIN.

MAX.

UNIT

positive supply voltage

−

8.8

V

storage temperature range

−25

+150

°C

operating ambient temperature range

−25

+70

°C