Re: Photomultiplier trans-impedance amplifier - DC eliminati
Micard,
While you get 40V when the PMT is coupled to an oscilloscope - what load do you have? Normally I would expect a transimpedance amplifier to be used. The the problem is how high you can have the transmipednace before the DC saturates the amplifier.
micard said:
Hi!
I'm looking for particular shape - gaussian. About the inductive load - would you suhhest gyrator?
No, I was thinking of simply an inductor. As I said, I am not sure whether it is ideal for your circumstances, but it has been done in some published papers, I and have done it that way once before. The problem is that you end up with a resonant circuit. In my case I actually used that and tuned it. In your case that may still work. You would need to add a resistor in parallel with the inductor to dampen the Q and stop ringing. The best way to experiment with the idea is with simulation.
micard said:
Hi!
What is the DC offset feedback loop?
It is not uncommon to design circuits where you take the output voltage (after a low pass filter) and feed the inverse back to the input to cancel out whatever is causing the offset. In your case you would need to sink the excess DC current from the PMT on the input to the transimpedance amplifier. It will work, but I would be concerned about injecting noise in to the input.
micard said:
Hi!
Would there be any use in trimm/balance pins of an opamp?
No. They will have very little effect as the offset isn't amplified in a transimpedance amplifier.
micard said:
Hi!
Unfortunately in this measurement system I'm looking for the fluorescence, which I need to stimulate by the laser. I cannot get rid of all the stimuli signal even with usage of razor edge filters.
All the fluoroscopy systems I have designed use photodiodes of various sizes. I don't remember having large DC signals because the optical filtering removes it. I am guessing your excitation and fluorescence wavelengths must be very close if that isn't the case with your system.
What wavelengths are you using?
I presume you have filtering of both the excitation and fluorescence wavelengths?
Is the DC offset actually optical or caused by leakage?
I have usually ended up with at least two stages - a transimpedance stage and a voltage amplifier. Total gains have been up to 2V/nA (using 3 stages in total). Leakage (dark current) becomes a problem at those sort of levels.
Keith.