مقسمات التردد .. كتاب التلفزيون الملون والعادي

2-19 Frequency Dividers:

Frequency dividers are used to obtain low frequencies from a fixed value high frequency.

The resulting frequencies can be fixed or programmed. When it is fixed, the frequency of the input signal is divided into a fixed number such as 2 - 5 - 75 - 181 - 256 - and the division factor can be programmed by changing the logical input of the divider - and integrated circuits (Ics) are used in the work of this divider, which has several types such as N or P or C and its types are:

RTL logic transistor resistance.

DTL Bi-Logic Transistor

TTL transistor logic transistor.

ETL is a way to connect a logical emitter and a logical circuit that can be contained in one or more chips.

Frequency divider working principle:

The frequency divider contains the following terminals: 1- Fixed-frequency signal input: It consists of continuous pulses of a specific frequency.

2- Several entries for the binary system, which determine the division factor, and it is represented by the number (0) binary and (1) binary, the number (0) is logical represented by the voltage (zero volts). The logical number 1 is represented by the voltage (5) volts.

In Figure (3-19), if the logical signal of the entrances is 1010, then the frequency divider is divided by the number (10), and multiple logical entrances can be used to divide by any number we choose. .

Added to the entrance circuit is a circuit that changes the division factor through switches, a rotary switch, or a computer output, and it is called the (LATCH) circuit.

3 - (Enable) or (START) input, which specifies the start of the PBX through an operating pulse

4 - (Reset) entrance, which is to reinitialize the divider.

5 - Output Signal.

In Figure (4-19), we find that the input signal has a fixed frequency (10) kHz - and the logical input to the divider is 1010) i.e. (10). When the start signal is received from (Enable) or (START) input, the splitter starts the counting process to end with the end of the number (1000) pulses. 1000 Hz, and in many practical applications, the output of the divider must continue until it stops its work or is reprogrammed, and this is done by applying the information of the (Latch) circuit (the latch circuit). This circuit is operated by switches or by rotary control or by a computer output.

Frequency Divider Practical Applications:

These applications are many and varied. If we assume that we would like to obtain a frequency (450 kilohertz) for special purposes from a fixed signal frequency (9 megahertz). And it comes true This is done by using a frequency divider on (10) Figure (6-19), and we apply its output to a frequency divider on (2). So the final obtained frequency is 9 megabytes + 20 = 450 kilohertz. We note that it is not possible to obtain the frequency with one frequency divider because the largest number that we divide by is the number (15), if the number of digits of the divider is /4/. The maximum number that the divider can divide by is calculated, if we assume that the number of digits is (N), so the division factor = 1-2. If the number of digits is p, the division factor for the frequency divider is (2 - 1 = 15), and if the number of digits is 12, the division factor for the frequency divider is 12 - 1 = 4095 times.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​The Counters

With the counter works like a frequency divider. They are logical circuits that produce pulses at the output proportional to the number of input pulses, and are less than that by dividing by the number N, which is the divisor. An example of this is a digital clock that divides the input pulses by (60) to give a pulse per second, then we divide this frequency by (60) to give a pulse per minute, and the output is divided by (60) also to get a pulse per hour. This counter counts the input pulses for a specified period of time