Hitachi C1421R User Manual

TDA8395 SECAM decoder
The TDA8395 is an alignment-free SECAM colou r decoder, including a Cloche filter, demodulator and line
identification circuit.
The Cloche filter is a gyrator-capacitor type.
lts frequency is calibrated in the vertical retrace period.
The calibration reference( pin 1 ) is obtained from the TDA8374 colour X-tal oscillator (pin 33).
Pin 7 is a decoupling for the Cloche reference.
The voltage change at this pin dueto leakage currents should be lower than 1 O mV, during field scan, resulting in a
capacitor of minimal100 nF.
Pin 8 is the reference capacitor for the PLL.
The voltage variation during field scan at this pin should be lower than 2 mV , resulting in a capacitor of 220 nF.
The sandcastle input (pin 15) is connected to TDA837 4 pin 41 and is used for generation of the blanking periods and
provides clock information for the identification circuit.
The CVBS source select output (TDA837 4 pin 38) supplies SECAM chroma to pin 16 of the TDA8395.
This is demodulated by a PLL demodulator, that uses the reference frequency at pin I and a bandgap reference to
obtain the desired demodulation characteristic.
lf the digitalline identification in the TDA8395 detects SECAM, pin 1 will sink a current of 150 (A out of TDA8374
SECAMref pin 33.
When the TDA8374 has not detected PAL or NTSC, it will respond by increasing the voltage at pin 33 from 1.5V to 5V.
Now the TDA837 4 colou r difference outputs pin 30 and 29 are made high-ohmic and the TDA8395 output pin 9 and 1 O
are switched on.
These outputs will be disconnected and high-ohmic when no SECAM is detected for two trame periods, the decoder
will be initialized before trying again.
SECAM-L and -L: application
For SECAM-L and L' the TDA8374 has to be switched to positive modulation via 12C-bus bit MOD.
SECAM-L' signals only occur in VHF band I and have their picture and sound carrier interchanged, compared to
SECAM-UPAL channels.
For SECAM-L' the IF picture carrier is situated at 34.2 MHz and the AM-sound carrier at 40.7MHz.
Therefore the IF-PLL reference has to be tuned away from 38.9 to 34.2 MHz.
This can be done via 12C-bus sub-address 15hex (IF-PLL).
The AM sound output is inserted at TDA837 4 externa! audio input pin via the SCART plug.
When bit MOD selects positive modulation for SECAM-UL', the TDA8374 automatically switches to externa! audio.
Base band delay line TDA4665
TDA4665 is an integrated double baseband delay line of 64 ~
lt couples to the TDA837 4 and TDA8395 without any switches o r alignments.
The TDA4665 consist of two main blocks:
- Two delay !ines of 64 sec in switched capacitar technique
- Internal clock generation of 3 MHz, line locked to the sandcastle pulse
The TDA4665 operates according to the mode demanded by the colou r transmission standard:
-For PAL it operates as geometric adder to satisfy the PAL demodulation requirements
-ln NTSC mode it reduces cross-colour interference (comb-filtering)
- For SECAM it repeats the colour difference signal on consecutiva horizontal scan lines.
A sandcastle pulse is connected to pin 5.
The top pulse voltage (should not exceed 5 V) can be directly coupled to the 5 V sandcastle output of the TDA8374.
11-UK

Hitachi C1421R Specifications

General

Brand	Hitachi
Model	C1421R
Category	TV
Language	English