# about clock in digital circuit?

Discussion in 'General Electronics Chat' started by Anikets, Aug 31, 2014.

1. ### Anikets Thread Starter New Member

Aug 6, 2014
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what is clock ? why it is necessery ? how to generate it?

Jul 18, 2013
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3,620
1/Measures time interval
2/ Depends what you are doing or timing
3/ Many ways depending on 1 & 2?
Max.

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3. ### Anikets Thread Starter New Member

Aug 6, 2014
11
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i mean to say in digital circuit, how clock is generated?

4. ### alfacliff Well-Known Member

Dec 13, 2013
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usually with a crystal oscilator and several counters used as deviders. sometimes the o=scilator is seperate from the mcu, and sometimes it is internal. some older home clocks used the line frequency 50 or 60 hz to provide timing for the clock.

Jul 18, 2013
13,135
3,620
Also R/C oscillator if precise timing period is not required in digital gate logic circuitry.
Max.

6. ### crutschow Expert

Mar 14, 2008
16,505
4,439
Most complex digital circuits are sequential, where the logic is performed in discrete steps (such as a computer). A timing pulse signal (called a clock) is used to control the operational steps and keep all the circuitry in proper sequence. (An example of a common clocked circuit element is a flip-flip.) This clock is a digital pulse train and normally operates at a constant high frequency, limited only by the operational speed and propagation delay of the various circuit paths. The clock has to allow enough time for all the circuits to settle to their new state before the next clock arrives.

The clock can be generated by a simple RC relaxation oscillator, or by crystal oscillators if the frequency is critical to maintain an accurate time sequence for the logic outputs.

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7. ### ScottWang Moderator

Aug 23, 2012
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>what is clock ?

A regular high low sequence as square wave.

>why it is necessary ?

It is like the heart for human, the heart compressing and pushing the blood, so we have a blood circulation in our whole body, and the same, the clock as the heart to pushing the high low signal to where they should go according to the designation.

>how to generate it?

google CD4069 oscillator, ne555 oscillator, crystal oscillator, and to see my blog.

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8. ### MrChips Moderator

Oct 2, 2009
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4,268
There are two classes of digital circuits, combinational and sequential.

In a combinational circuit, the behaviour of the circuit is determined by input parameters.
For example, if there are four input parameters a, b, c, d, the output Q of the circuit can be expressed as a function of a, b, c, and d:

Q = f(a, b, c, d)

In a sequential circuit, the element of time and the current state of Q must be considered. Hence the next outcome of Q at time n+1 can be expressed as:

Qn+1 = f(a, b, c, d, Qn)

Thus the transition from Qn to Qn+1 is dependent on time. That is the purpose of the CLOCK signal. The CLOCK determines when the transition from one state to the next state occurs.

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9. ### Anikets Thread Starter New Member

Aug 6, 2014
11
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sir could you please tell me practical example for this?