# Help: how to realize the following function?

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#### Owen Hao

##### Newbie level 4
Hi
These days I am required to design a following circuit: distinguish a pulse's duty cycle without clock aided. The input signal is a series pulse with different period and
different duty cycle. And no clock is available, also creating a clock is not allowed because of low power. I must identify whether each pulse's duty cycle is more or less than 50%. Is possible to design this circuit just using digital blocks?? Anyone could give me a valuable clue for that?

//Bow
:|

#### zorro

Hi Owen,

I suppose that your signal is periodic, and that it has two definite (digital) levels 0 and V.
Passing that signal by a low pass filter with unity gain, the output is V*duty_cycle. Comparing this level with V/2 gives you the solution. The filter can be as simple as a single RC cell.
Regards

Z

#### Owen Hao

##### Newbie level 4
Hi Zorro
Thanks for your suggestion. I have tried the analog way, but there always is a tradeoff between the rosolution and current consume, that's why I hope design the circuit only with digital blocks. If the input signal's frequency could be doubled with digital way(for example, generate a 2MHz signal when input is 1MHz),I think it's very helpful to my supposion. Do you think it's possible or not?

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