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Combinational logic for frequency division

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Junior Member level 3
Jan 14, 2003
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It came up in a general banter session to check if it's possible to divide frequency of a digital waveform by only using combinational logic (of course with no output fed back to inputs)? It's quite easy to create a frequency multiplier. But is a frequency divider possible?


If you connect 2 JK flip-flops in series you can divide frequency in two ,3 JK flip flop you can divide 4 ...

All the Js and Ks are connected to logic 1
Signal--->CLK1 Q1--->CLK2 Q2----->CLK3 ....

With due respect, please read the topic patiently while you plan to post a solution. The point is use of only combinational logic for frequency division. A flip flop is an inherent sequential circuit. So that isn't the solution. In fact it's a T flip flop that we should use where J and K are tied high. The question is usage of combinational gates without feedback.

hi friend,

actually i guess we can realize ff using muxes right ? would that not be enough..

If not do tell abt the comb freq multiplier and divider both.. its interesting ..

So let me level set before we try finding a solution.

You can actually construct a frequency multiplier by passing a signal through an XOR gate while the other input is tied to the delayed version of the first input. For example you can tie input A to the signal and input B to the signal that passes, lets say, 10 invertors. Now this, because of the propagation delay, will generate pulses where the two inputs were out of phase with each other. And since this occurs twice every cycle, we have an output thats twice the frequency of the input signal.

The question now is on a similar setup or a complex one is it possible to come up with a frequency divider. Your multiplexor example is still not good, because you will tie the output to one of the inputs of the multiplexor thus a feedback from output to the input exists.

More bluntly put, is it required to "remember any previous value" for a circuit that you would construe to divide the frequency?

I hope I made it clear. It may happen that we do not have a circuit at all. But if we have that'd be a great debate on it!

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