The second phase detector
-2 locks the phase of the horizontal drive pulses at output pin 40 to the
horizontal flyback pulse at input pin 41.
This compensates for the storage time of the horizontal deflection transistor.
The
-2 loop filter (C) is externally connected to pin 42.
The horizontal phase can be given a static off set via IIC bus (HSH "horizontal shift).
A dynam ic correction is possible by current feedback into the
-2 loop filter capacitor.
To protect the horizontal deflection transistor, the horizontal drive is switched off immediately
when a power failure ("Power-On Reset "bit POR) is detected.
The power failure may have corrupted the contents of the internal data registers, so the TDA8374 should be started up again.
The TDA8374 has a separate supply input (pin 37) that only used as a clean supply voltage for the horizontal
oscillator circuits.
7-4. Vertical Synchronization
The vertical sawtooth generator drives the vertical output.
It uses an external capacitor at pin51 and a current reference resistor at pin 52.
The TDA8374 vertical drive has differential current outputs for DC-coupled vertical output stage, like the TDA8356.
At TDA8356 input pins1 and pin2 this current is converted into a drive voltage via a resistor.
7-5. Geometry processing
W ith the TDA8374 is possible to im plement autom atic geometry alignment, because all parameters are
adjusted via the IIC bus.
The deflection processor of the TDA8374 offers the following five controls;
- Horizontal shift
- Vertical slope
- Vertical amplitude
- Vertical s-correction
- Vertical shift
7-6. Colour decoder
The colour decoder contains an alignm ent-free X-tal oscillator, a dual killer and difference demodulators.
Together with the TDA8395 SECAM add-on a multi standard PAL/SECAM/NTSC decoder can be built
with automatic reconition.
W hich standard can be decoded depends on the external X-tal used.
Two X-tal pins (34 and 36) are present so normally no external switching is required.
The IC m ust be told which X-tals are connected (bit XA and XB).
This is important, because the X-tal frequency of the colour decoder is also used to calibrate many
internal circuit. The burst phase detector locks the X-tal oscillator with the chroma burst signal.
The phase detector operates during the burst key period only, to prevent disturbance of the PLL by
the chrom a signal. Two gain m odes provide:
- G ood catching range when the PLL is not locked.
- Low ripple voltage and good noise imm unity once the PLL has locked.
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ACEC
