دارة (حلقة حجز الطور) .. كتاب التلفزيون الملون والعادي

19-3 The Phase-Locked Loop: (PLL)

This circuit is not completely modern, but it is used in television sets in two circuits

Often they are:
1- The horizontal AFC circuit, i.e. the automatic frequency control) and in the horizontal oscillator.

2- The (AFPC) circuit (Automatic Frequency Page Adjuster) and an oscillator (4.43) MHz for the color sub-carrier signal frequency. The (PLL) circuits are located in the digital frequency divider in order to regulate and stabilize the wide-range frequency tuning circuits found in the UHF-VHF TV electors.

The work of PLL circuits depends on comparing two signals and generating a correction proportional to the frequency or page difference between them - and this effort then changes the frequency or page difference of one of the two signals to make it the same frequency and page as the fixed signal. The two signals in general are from a voltage controlled oscillator (VCO), and a stable reference frequency crystal oscillator.

The PLL circuit creates a voltage appropriate to the difference in page and frequency between the VCO and the reference crystal oscillator. This voltage (called the correction voltage or error voltage) is used to adjust the VCO output signal to match the crystal oscillator.

PLL working principle:

The work of the PLL circuit secures the signal with constant frequency and page, by generating the appropriate correction voltage for the difference between the micro-frequency crystal oscillator and the voltage controlled oscillator (VCO) after applying the two frequencies to the page comparator - the output of the page comparator that generates direct current is filtered DC and applied to the voltage controlled oscillator ( VCO) to set its frequency and page. the shape

(19 - 7) The frequency of the crystal oscillator can be much higher than the frequency of the oscillator (VCO), if we want a fixed frequency.

For example, (10) kHz and the frequency of the crystal oscillator is (20 MHz). A frequency divider should be used on (2000), so the output of the divider will be a signal (10 kHz) with reference crystal stability to adjust the voltage-controlled oscillator (VCO) and ensure the stability of its frequency.

It is worth noting that a low frequency crystal oscillator is not available, because such an oscillator is very expensive.

The use of the PLL circuit in TV voters:

The PLL circuit is included in the MPU or AP microprocessor microprocessor, which can provide fine tuning for all VHF and UHF channels electronically, without the need for a fine tuning controller (FTC). Because the correct synthesis of each is done accurately and automatically, and the integrated circuit that represents the PLL circuit contains 1153 transistors. While the integrated circuit of the microprocessor includes (11029) a transistor channel.

19-4 Microcomputer (C):

​​​​​​The mini computer is a complete (computer) on a single chip or on several chips - and the computer is somewhat similar to the human brain, as it stores information in memory - and then extracts the necessary information from this memory when it is needed - and it has the ability to Perform many operations.

Computer departments (computer):

Every computer has three main parts:

1- Memory.

2 - Central Processing Unit (CPU).

3 - Entrance and Exit (1/0).

Memory stores instructions and information necessary and sufficient to perform its work - and there are those
There are two types of memory, the first is a (Reading Only Memory) (ROM), which stores previously specified information that remains unchanged. The second memory is Read And Write Memory (RAM), which receives and stores new information. It is variable on demand.

Central processing unit: (CPU)

It is the one that processes the information step by step, according to the specific programs stored in the memory. It directs and controls the work of the computer, so it is called (microprocess).

A - The Input section enters information into the (CPU).

B- The Output department receives the information that the CPU outputs and outputs it in an understandable form.

Computer capability:

Basically, the computer performs very simple operations in every small part of the time, but what distinguishes it is the very high speed in which it accomplishes these operations. For example, a program that involves processing (10,000) pieces of information seems very complicated and takes a long time to complete, but the computer is able to process and complete these operations in several milliseconds, and this enormous and imaginary speed makes us say: The computer has limitless capabilities. In fact, each computer has specific capabilities that are determined by many factors.

The instructions for A3 lead you to put the value 3 in H8 and here you write the number 3 in the starting point and advance to A8.


A8 - Subtract the amount from the expression in H7 » and instructions A6 direct you to put the number 9 in H7 and so on 9-3=6.

B1 - If the value found is not zero, advance to B3.

B3 - If the value is a negative number, advance to B5.

B4 - If the amount in H7 is greater than the amount in H8 stop.

And notice that you start at square A1 and work your way up to A4-A3-A2 and so on. And this is a very simple computer program, and how it does very simple operations in every tiny fraction of time - but a computer can do thousands of operations in a millisecond.

Thus the application of the microcomputer in the television voter system is no longer surprising. Digital electronics - microcomputers - dividers and others deserve attention and study because they will be widespread in household uses
industrial and its equipment