TDA8505 Datasheet, PDF (10/32 Pages) NXP Semiconductors – SECAM encoder

Philips Semiconductors
SECAM encoder
Preliminary specification
TDA8505
Sync separator and pulse shaper
The composite sync input at pin 29 together with the
outputs of the 272 divider of the 4.250 MHz reference loop
are the sources for all pulses necessary for the processing.
The pulses are used for:
• Clamping
• Video blanking
• FH/2
• Chrominance blanking
• Stop/start of modulator
• Vertical identification
• Timing for the modulator control
• Sandcastle pulse shaping at pin 20.
External FH/2 at pin 4 is only necessary when two or more
SECAM encoders have to be locked in the same phase.
The phase of the internal FH/2 can be locked with an
external FH/2 connected at pin 4. A reset of the internal
FH/2 is possible by forcing pin 4 to a HIGH level. This
HIGH level corresponds with D'R. Pin 4 is connected to
ground when not used.
Figures 9 and 10 show the generated pulses during
vertical blanking for PLL tuning or crystal tuning
respectively. Figure 11 shows the pulses during line
blanking.
Transcoding application
A sandcastle pulse is necessary for the PAL/NTSC
demodulator (i.e. TDA4510) for transcoding PAL or NTSC
to SECAM.
Most of the demodulator ICs use a sandcastle pulse with
an amplitude of 12 V or 8 V. A 12 V or 8 V sandcastle is
not possible with the TDA8505 because of the 5 V power
supply.
To generate a 3-level sandcastle pulse at pin 20
(see Fig.8) an external supply voltage must be connected
to pin 19.
The PAL or NTSC CVBS signal is connected to the
composite sync input (pin 29) for PLL tuning and pulse
shaping. As previously mentioned the Y input at pin 5 can
be used as the Y+SYNC input for the filtered Y+SYNC PAL
or NTSC signal, when pin 12 is at a HIGH level.
handbook, full pagewidth
V _ext
4.5 V 0.2 V
2.5 V 0.2 V
MSA733 - 1
0.5 V
Fig.8 3-level sandcastle pulse.
July 1994
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