OPA657: OPA657 oscillation problem

Hello Ozge, 

It would help to see the whole circuit but in any case you always have to compensate the Zt design with a feedback capacitor. That is all described in this high speed presentation. most importantly, we would need the source capacitance. There is an article about to publish that steps through this in a pretty simple fashion, but you might also take a look at the new OPA8187180.Transimpedance design flow using high speed op amps.pptx

Sorry for late response, i was busy with health problems. Our circuit is above. I will read articles and opa818 datasheet.

Thank you very much,

Ozge

SOory you were not well Ozge, 

This is not quite enough, this does not now look like transimpedance, looks like a voltage gain? where do R1 and R4 go? And R2, 1kohm seeems large for R2. Is the 1pF intentional or parasitic? 

Sorry for quick answer and missings. R1 is input and it goes to function generator or  photomultiplier tube output. R4 goes to ground, there was a parallel capacitor actually. But we do not use this resistor and capacitor, they are short-circuited. Supply capacitors are between +/- supplies and ground. R2 is output and it is 50ohm. Input and output 50ohm is for impedance matching as my supervisor says. 1pF is intentional, my supervisor says it reduces the noise and DC signals.

By the way, i'm not sure this circuit is effective. We tried different resistors(1.8k,2k,5k,10k) but these are not enough for low and high frequencies.

Thank you,

Ozge

wow, well lets be careful here, 

So a signal generator and a PMT will have completely different source impedances, pick one, 

your supervisor is handwaving through some subtle issues. feedback caps can work, less so with decompensated parts. 

There is a lot of somewhat difficult material out there that deals with these things, here is one, tell me what you are trying to do - 

https://www.planetanalog.com/author.asp?section_id=3404&doc_id=565165&