TA7609P Synchronous Separation Circuit

The circuit shown is the synchronous separation circuit in ICTA7609P, and its working principle is similar to the above. c is an amplitude separation tube. The negative full TV signal passes through the isolation resistor 3R01, and is added to the base of Q1, that is, pin 16, through the coupling capacitors 3C01 and 3D01. When no signal is added, there is no base bias, and Q1 is cut off. When the synchronization pulse arrives, the input terminal is at a high level. At this time, 3D01? and Q1 are both turned on, and 3C01 is charged. Due to the small charging time constant, 3C01 is charged with a voltage close to the amplitude of the synchronization pulse. After the synchronization head passes, 3C01 is discharged through 3R02. The time constant is large and the discharge is very slow, so there is a reverse bias voltage on 3C01? for Q1. It keeps Q1 cut off during the positive scanning process, so that the collector of Q1 separates the negative polarity of the horizontal and field composite synchronization pulses, which are supplied to the phase detector of the automatic phase control of the horizontal scanning system as the horizontal synchronization signal. 

   The composite synchronization pulse separated from the collector of Q1 is shaped and amplified by Q2~Q5, and then output from pin 14, which is supplied to the field scanning system for integration as a field synchronization signal. At the same time, the composite synchronization is also used as the color synchronization selection pulse of the color decoder and the clamping pulse of the brightness channel. 3C02 and 3D01 form an anti-pulse interference circuit. Due to 3C02 and 3D01, once a large-amplitude narrow interference pulse arrives, 3C02 is quickly charged with a higher voltage, while the voltage on 3D01 does not change much due to its large capacity and slow charge change. After the interference disappears, 3C02 is quickly discharged through 3D01, causing the very negative bias caused by the large pulse interference to drop rapidly, thereby ensuring normal cutting of the circuit.