HELP: how to identify a pulse's duty cycle?

[Owen Hao]

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? :|

 

[mnkeis]

Hi
I think you can use two capacitors and a comparator, you charge one capacitor whit the positive pulse and the other with the negative pulse, the comarator will determine you if duty is above or below 50%.
It's just an idea, hope be phisically possible and helpful for you
Regards

Mauro

 

[sixth]

you can measure the average of the input pulse series by using a analog filter and then compare this value with a reference voltage, but this method is only valid for long term condition. if you want to determin the duty cycle quickly, this method is not valid, can you tell out the time you need to identify the pulse's duty cycle?

 

[Owen Hao]

Hi Sixth&mnkeis:
Thanks for you suggestion. The period is between 0.75us and 50us. I am not liable to use analog filter because I think its resolution is not enough. I am still trying the purely digital way. But it seems very hard.