ILA8362ANS (8A)
FUNCTIONAL DESCRIPTION
Video IF amplifier
Synchronisation circuit
The IF amplifier contains 3 AC-coupled control stages
with a total gain control range of greater than 60 dB and
sensitivity 70 μV.
The sync separator is proceeded 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 reference carrier for the video demodulator is
obtained by means of passive regeneration of the picture
carrier. The external reference tuned circuit is the only
remaining adjustment of the IC.
The separated sync pulses are fed to the first phase
detector and to the coincidence detector. The coincidence
detector is used for transmitter identification and to detect
whether the line oscillator is synchronised.
The polarity of the demodulator can be switched so that
the circuit is suitable for both positive and negative
modulated signals.
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 AFC circuit is driven with the same reference signal
as the video demodulator. The AFC output voltage is 6 V.
The AGC detector operates on levels, top sync for
negative modulated and top white for positive modulated
signals. The AGC detector time constant capacitor is
connected externally. This is mainly because of the
flexibility of the application.
The circuit employs a second control loop to generate the
drive pulses for the horizontal driver stage.
The time constant of the AGC system during positive
modulation is slow, this is to avoid any visible picture
variations. This, however, causes the system to react very
slowly to sudden changes in the input signal amplitude.
X-ray protection can be realised by switching the pin of
the second control loop to the positive supply line. The
detection circuit must be connected externally. When the
X-ray protection is active the horizontal output voltage is
switched to a high level. When the voltage on this pin
returns to its normal level the horizontal output is
released again.
To overcome this problem a speed-up circuit has been
included which detects whether the AGC detector is
activated every frame period.
The circuit contains a video identification circuit which is
independent of the synchronisation circuit. Therefore
search tuning is possible when the display section of the
receiver is used as a monitor. In the normal television
mode the identification output is connected to the
coincidence detector, this applies to all three devices. The
identification output voltage is LOW when no transmitter
is identified. In this condition the sound demodulator is
switched off (mute function). When a transmitter is
identified the output voltage is HIGH. The voltage level
is dependent on the frequency of the incoming
chrominance signal.
The IC contains a start-up circuit for the horizontal
oscillator. When this feature is required a current of
5.5 mA has to be supplied to pin 36. For an application
without start-up both supply pins (10 and 36) must be
connected to the 8 V supply line.
The drive signal for the vertical ramp generator is
generated by means of a divider circuit. The RC network
for the ramp generator is external.
Integrated video filters
The circuit contains a chrominance bandpass and trap
circuit. The filters are realised by means of gyrator
circuits and are automatically tuned by comparing the
tuning frequency with the crystal frequency of the
decoder.
Sound circuit
The sound bandpass and trap filters have to be connected
externally. The filtered intercarrier signal is fed to a
limiter circuit and is demodulated by means of a PLL
demodulator. The PLL circuit tunes itself automatically
to the incoming signal, consequently, no adjustment is
required.
When the pin is left open-circuit the trap is switched off
so that the circuit can also be used for S-VHS
applications.
The luminance delay line and the delay for the peaking
circuit are also realised by means of gyrator circuits.
Colour decoder
The colour decoder in the various ICs contains an
alignment-free crystal oscillator, a colour killer circuit
and colour difference demodulators. The 90° phase shift
for the reference signal is achieved internally.
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IKSEMICON [ IK SEMICON CO., LTD ]
