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TDA1180 View Datasheet(PDF) - STMicroelectronics

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TDA1180
ST-Microelectronics
STMicroelectronics ST-Microelectronics
TDA1180 Datasheet PDF : 12 Pages
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TDA1180P
Pin 10 - Vertical sync output
The vertical sync pulse, obtained by internal inte-
gration of the synchronizing signal, is available at
this pin.
The output impedance is typically 10kand the
lowest amplitude without load is 11V.
Pin 11 - Coincidence detector
From the oscillator waveform a gate pulse 7 µs
wide is taken whose phase position is centered on
the horizontal synchronism.
The gate pulse not only controls a logic block which
permits the sync to reach the oscillator-sync phase
comparator only for as long as its duration, but also
allows the latching and de-latching conditions of
the oscillator to be established.This function is
obtained by a coincidence detector which com-
pares the phase of the gate pulses with that of the
sync.
When the two signals are not accurately aligned in
time it means that the oscillator is not synchronized.
In this case the detector acts on the logic block to
eliminate its filtering effect and on the time constant
switching block to establish a high impedance on
Pin 12 (small time constant of low-pass filter).
This latter block also acts on the oscillator-sync
phase detector to increase its sensitivity and with it
the loop gain of the synchronizing system.
In this conditions the phase lock has low noise
immunity (wide equivalent noise bandwidth) and
rapid pull-in time which allows fairly short synchro-
nization times.
Once locking has taken place the coincidence de-
tector enables the logic block, causes a low imped-
ance on Pin 12 and reduces the sensitivity of the
phase comparator.
In these conditions the phase lock has high noise
immunity ( narrow equivalent noise bandwidth) due
to the complete elimination of interference which
occurs during the scanning period and the greater
inertia with which the oscillator can change its
frequency.
To optimize the behaviour of the IC if a video
recorder is used, the state of the detector can be
forced by connecting Pin 11 to earth or to + VS. The
characteristics of the phase lock thus correspond
to the lack of synchronization.
Pin 12 - Time constant switch, (see Pin 11)
Pin 13 - Control current output
The oscillator is synchronized by comparing the
phase of its waveform with that of the sync pulses
in the oscillator-sync phase comparator and send-
ing its output current I13 (proportional to the phase
difference between the two signals) to Pin 15 of the
oscillator after it has been filtered properly with an
external low-pass circuit.
The time constant of the filter can be switched
between two values according to the impedance
presented by Pin 12.
The voltage limiter at the output of the phase
comparator limits the voltage excursion on Pin 13
and therefore the frequency range in which the
oscillator remains held-in.
The output resistance of Pin 13 is:
q low when V13 > 4.3 or V13 < 1.6V
q high when 1.6V < V13 < 4.3V
To prevent the vertical sync from reaching the
oscillator-sync phase comparator along with the
horizontal sync,a signal which inhibits the phase
detector during the vertical interval is taken from
the vertical output stage; inhibition remain even if
the video signal is not present.
The free running frequenc of the oscillator is deter-
mined by the values of the capacitor and of the
resistor connected to Pins 14 and 15 respectively.
To generate the line frequency output pulses, two
theresholds are fixed along the fall ramp of the
triangular waveform of the oscillator.
Pin14 - Oscillator (see Pin 13)
Pin 15 - Oscillator control current input (see
Pin 13)
Pin 16 - Ground
9/12
 

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