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detect pulse of 140ns and 50mv.

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hiren_dave

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Hi,

i want to detect a pulse with 140ns and 50mV amplitude. i want to design such a circuit when pulse comes pic microcontroller should get an interrupt. how can i do that?

thanks in advance...
 

Use a fast comparator, e.g., LT1719. The output of the comparator would go to one of the interrupt pins on the PIC.

Do you need to measure the width of the pulse, or just interrupt when any pulse occurs?
 
thanks friend. I want just to interrupt microcontroller.
currently i am using lm 324 / lmc6482in ic for opamp and HCF4098b pulse stretcher that can stretch a pulse. but i am not getting a pulse. is these IC are good enough ? Should i buy lt1719? please suggest me...
 

now, i have changed my opamp to MC33274AP (on semiconductor) and pulse stretcher is CD4098BE(texas).
 

now, i have changed my opamp to MC33274AP
Click to expand...
You'll notice that neither slew rate nor GBW are promising to convert the pulse into a correct logic level. Why not using a fast comparator, as suggested? TLV3501 would be another nice part.
 
FvM said:
You'll notice that neither slew rate nor GBW are promising to convert the pulse into a correct logic level.
Click to expand...

hi FVM,

ic MC33274AP resides with me. i will purchase IC TLV3501 until i am testing with MC33274AP ic. I can't understand this quate. why it will not work? please explain. honestly, i am a person with lower technical knowledge.
 

Because you have such a narrow pulse, you need a fast opamp (or comparator) to measure it. The MC33274AP is just too slow to respond to that short a pulse. The slew-rate parameter tells you how fast the output can change. The MC33274AP has a SR of 10V/u-sec. That means for a 140ns pulse input, the output will only change (optimistically) 1.4 volts. (140ns x 10V/usec).

The TLV3501 with a 5V supply, by comparison, will change 4 V in 1.5nS.
 
hi friends,

Finally i got the pulse using MC33274AP opamp and cd4098 pulse stretcher. thanks to all for being with me.
 

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