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help to build preamplifier circuit....

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jawadali477

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hi,
can anyone help me in building preamplifier circuit? the signal that is going to be received has 30 nanosecond pulse width. any help will be appreciated.

thanks

jawad
 

It depends on the nature of the signal. Current or voltage? High or low impedance? An opamp would be the easiest way.

Keith
 

hi,
its current. my concern is basically what type of op amp should i use? should it has high slew rate? if yes, what slew rate should it have? secondly i'm using S1223 pin photodiode. will it work for detecting such signal i.e 30 nanosecond?
 

I would say the S1223 is far to big and slow for looking at 30ns pulses. For the amplifier you need to search for transimpedance amplifiers.

Keith.
 
hi,
thanks Mr. Kieth for the concern.
how about using phototransister (instead of photodiode)?

regards

jawad
 

Absolutely not! They are far too slow. Hamamatsu devices are fine but for that speed you need something smaller. Have a look at the selection guide **broken link removed** and look for something 300MHz or more.

Keith.
 
i didn't understand the term slow. can you please make me understand this phenomenon?

thanks
jawad
 

You want to detect a 30ns pulse. That is a fast pulse and you need a fast photodiode to see it. It is all relative. A phototransistor may have a response time of several microseconds so wouldn't see a 30ns pulse at all.

Keith.
 
thank you so much Mr. Kieth. i really appreciate your concern and the information you provided to me.

thanks

jawad
 

I believe a good fast charge amplifier with a photodiode in the photoconductive mode is a nice solution. The diode is reverse biased into the charge amp. You can null the dark current by using a second similar diode. There is a pretty good reference circuit somewhere on the Analog devices website for a 10nS rise time amp using an HP diode.
 

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