Electronics > Projects, Designs, and Technical Stuff
High Speed Transimpedance Amplifier
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arivalagan13:
Hello all,
I'm in the process of designing a transimpedance amplifier for an analytical instrument. The requirement is such that the process generates a very low current which is multiplied by microchannel plate. Even after this, the current is between 1 to 5 pA and the bandwidth requirement is around 300 MHz. The transient response requirement is also very high.
I've designed a transimpedance amplifier with OPA656 which is a 500MHz unity gain-bandwidth product opamp. I've installed a 1Gohm feedback resistor..I'm about to sweep this resistor value in order to find the correct resistor value to faithfully amplify the current signal.
For testing purposes, I use an old photodiode..whose specifications I don't know clearly.

My questions are:
what are the systematic steps I should follow to design the amplifier?
2. I don't have ready-made access to sophisticated measuring instruments like keysight/Tektronics DSO and the like.
Having said that suppose I want to characterize the frequency response and transient response of the amplifier.
But, function generators can only generate voltage sources...or how do I generate current sources in order to measure the frequency response of the TIA.....or whether the facility of generating current sources is available with the function generator?
3.I've the same question for measuring the transient response of the TIA

to put in other words: How do I measure the frequency response of the transimpedance amplifier? and How do I generate such a small current in order to measure the frequency response and the transient response..

Kindly provide necessary support in this regard.

Regards,
M Arivalagan
Research Scholar
Anna University
Chennai
Tamilnadu
Ph.:+91 75023 98999
email: arivalagan13@gmail.com
StillTrying:

--- Quote from: arivalagan13 on June 10, 2019, 03:55:57 pm ---the current is between 1 to 5 pA and the bandwidth requirement is around 300 MHz. The transient response requirement is also very high.
...
I've installed a 1Gohm feedback resistor..
--- End quote ---

I think you're beyond what can be done by a factor of about 10 million, hopefully I'm wrong though. :-[
awallin:
gotta learn to walk before you run... try this for a start:
https://electrooptical.net/static/oldsite/www/frontends/frontends.pdf
DaJMasta:
Hamamatsu also has some designs for high speed photodiode circuits available as app notes with some of the important considerations mentioned.

A lot has to do with parasitic capacitance of the system, the photodiode itself is a significant component so using any old photodiode may not give you the performance of the rest of the circuit.  Of course, the capacitance of the amp matters, but I believe the Hamamatsu app notes also mention that breaking the feedback resistor into a series string of feedback resistors also helps reduce the capacitance on the path.
Kleinstein:
For a fast system the FB resistor should only be as large as needed to get the noise low enough.
I would start with increasing the gain of the micro-channel plate to get more signal to start with.
I would suspect that one may need to go discrete fets and possibly not silicon based any more. If small and thus low capacitance, one may not need a TIA anymore.
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