طريقة إخماد التشويش لتحسين عملية التزامن .. كتاب التلفزيون الملون والعادي

13-4 The noise suppression method to improve the synchronization process:

The interference or noise greatly affects the synchronization pulses - and its bad effects appear more clearly and deeper than the interference on the visual or audio signal - the eye and the ear
Humanity can ignore - to some extent - some distortion of the image or sound. Whereas, a single jamming pulse at a specific moment badly disrupts the horizontal or vertical synchronization, so the picture is completely disrupted. Therefore, every television receiver inevitably includes a circuit to dampen this interference or remove it and keep its effect away from the synchronization pulses. Figure (9-13) shows a synchronization separator circuit diagram. With jammers, the circuit consists of transistor Q2 connected in series with the emitter of synchro separator transistor Q1. When the jamming barrier circuit is open, as well


In the normal state, the voltage between the collector and the emitter is only (3 volts), and the synchronization separator works normally. But when the jamming barrier circuit is closed, the separator emitter voltage rises to 20 volts. This voltage comes through the resistance R1 from the supply point + 20 volts, and because of the positive bias in the radiator of the synchronization separator, any synchronization pulse does not take its place.

But what is the reason for closing the jamming barrier? We note that the jammer circuit is energized by the visible signal, along with the negative synchronization pulses, while the separator circuit is occupied by the in-phase visible signal - The normal visible signal applied to the jammer transistor does not have enough amplitude to overcome the R2 bias, however, if the sharp jammer pulses are above The synchronization pulse will close the jamming barrier, but the jamming pulses that are not wider than the peak of the synchronizing pulses will not cause it to close. The synchronization pulses are separated in the filtering circuit of the transistor collector Q1 so that the horizontal pulses go in a special way, and the vertical ones in a different way, and we will study later. It shows a simplified separator circuit synchronizing with a jamming inverter and other circuits contained in this one-layer silicon integrated circuit. . That's a circuit

13-5 Separating the vertical from the horizontal pulses:

The working principle of this separator depends on the different frequency or waveform of the vertical and horizontal pulses other than the equal amplitude of the pulses in both. The task of separating the two types of pulses is carried out by frequency filters, consisting of a resistance and an RC capacitor, each of which has a specific time constant by law (TR.C). Figure (10-13):
where :

T is the time constant in seconds.

R is the resistance value in ohms.

C is the capacitance of the capacitor in farads.

If a capacitor C is charged through a resistance R, the rate of charge of the capacitor is proportional to the value of the resistance. The voltage increases on both ends of the capacitor while it decreases on both ends of the resistance, so that their sum is equal to the voltage of the source. If we close the circuit on the same resistance R after separating the primary source, the capacitor discharges its charge through the resistance, so the voltage decreases between the two ends of the capacitor, and increases on both ends of the resistance according to the curve drawn in the shape (13 - 11).
If the required output is the voltage on both ends of the resistance, then it is called the circuit

(differentiation circuit)

But if the required output is the voltage on both ends of the capacitor, then the circuit is called (integration circuit).

Using the differential circuit to separate the horizontal pulses:

When the synchronization pulse enters the differential circuit, it leads to the generation of two sharp pulses at the outlet of the circuit, one positive and the other negative, as in Figure (13-13). The first sharp pulse is generated due to the front edge of the synchronization pulse, so the capacitor is charged, and the second sharp pulse is generated when the back edge of the synchronization pulse arrives, so it discharges capacitor . The synchronization circuit is designed so that its time constant is equal to 1/5 of the horizontal synchronization pulse - in fact, we take advantage of one of the two sharp pulses in adjusting the horizontal oscillator, which is the mostly positive differential pulse, and this oscillator also continues to be controlled while receiving the vertical pulses. Which prevents the occurrence of any defect or disturbance in its control. The differential circuit can be called a filtering and passing circuit for high frequencies