September 1994
5
Philips Semiconductors
Preliminary specification
Integrated NTSC decoder
and sync processor
TDA8315T
FUNCTIONAL DESCRIPTION
CVBS or Y/C input
The TDA8315T has a video input which can be switched
to CVBS (with internal chrominance bandpass and trap
filters) and to Y/C (without chrominance bandpass and
trap filters). The switching between CVBS and Y/C is
achieved by the DC level of the CHROMA input (pin 15).
Integrated video filters
The circuit contains a chrominance bandpass and trap
circuit. The filters are realised by gyrator circuits that are
automatically tuned by comparing the tuning frequency
with the crystal frequency of the decoder. The
chrominance trap can be switched off by the DC level of
the CHROMA input.
The luminance delay line is also realised by gyrator
circuits.
Colour decoder
The colour decoder contains an alignment-free crystal
oscillator, a colour killer circuit and colour difference
demodulators. The gain of the two colour difference signal
demodulators is identical and the phase angle of the
reference carrier signals is 90
°
. This phase shift is
achieved internally. It is possible to switch the demodulator
angle to 110
°
by an internal matrix circuit. The switching is
obtained externally via pin 8.
Synchronization circuit
The sync separator is preceded by a voltage controlled
amplifier which adjusts the sync pulse amplitude to a fixed
level. The sync pulses are then fed to the slicing stage
(separator) which operates at 50% of the amplitude.
The separated sync pulses are fed to the first phase
detector and to the coincidence detector. The coincidence
detector is used to detect whether the line oscillator is
synchronized. The PLL has a very high static steepness,
this ensures that the phase of the picture is independent of
the line frequency. The line oscillator operates at twice the
line frequency.
The oscillator network is internal. Because of the spread of
internal components an automatic adjustment circuit has
been added to the IC.
The circuit compares the oscillator frequency with that of
the crystal oscillator in the colour decoder. This results in
a free-running frequency which deviates less than 2% from
the typical value.
The horizontal output pulse is derived from the horizontal
oscillator via a pulse shaper. The pulse width of the output
pulse is 5.4
μ
s, the front edge of this pulse coincides with
the front edge of the sync pulse at the input.
The vertical output pulse is generated by a count-down
circuit. The pulse width is approximately 380
μ
s. Both the
horizontal and vertical pulses will always be available at
the outputs even when no input signal is available.