High Speed Low Gain Current Amplifier?

[AmanNVI]

Hi gents,

I have a current signal from a detector (PMT) which is being sampled once every 2 to 2.4 nS.
The current output from my detector ranges from 0-2 mA.
The current input on my A/D converter / op amp expects a 0-10mA signal. The voltage values range from 5 - 25V of PMT output.

I can't change the detection electronics, so I was thinking I could use a simple collector-base transistor setup to increase the current (common collector design) like this one (on right)
**broken link removed**

I tried a setup using an NPN for this - but it inverted and amplified the current signal. I guess this makes sense as I think this is a "Class A" amplifier.

So my question is, is this the best way of achieving high speed low gain amplification of current? If yes I can add another transistor, and re-invert the signal. If there's a better way, i.e. an op-amp or low gain amp that will keep up with the speed needed, I'd go for it. My major concern is that I don't want to reduce the signal quality from the PMT. This is for a very low light laser scanning application, so signal quality is of top priority.

I apologize in advance of my questions are lacking a deep understanding here - I know enough only to be dangerous

Any advice is greatly appreciated!

 

[Ow@i$]

I suggest to use an opamp in an inverting configuration, and you can also that way can control the gain depending upon your values... signal too will be the same!!!

 

[crutschow]

What is the maximum frequency and/or rise-time of the signal from the PMT detector?

 

[AmanNVI]

I suggest to use an opamp in an inverting configuration, and you can also that way can control the gain depending upon your values... signal too will be the same!!!

Thanks so much for your reply Smoothcriminal! I've considered this, one question I have is whether using an op amp would introduce any additional signal degradation. I'm not familiar enough with them to know the answer to this, but you and some other sources who are obviously far more knowledgeable than I have suggested this, so I'll definitely try it out!

-Aman

 

[crutschow]

............... I've considered this, one question I have is whether using an op amp would introduce any additional signal degradation. ...................

It depends upon the signal voltage level, frequency, and/or minimum risetime. Hence my previous question.

 

[AmanNVI]

It depends upon the signal voltage level, frequency, and/or minimum risetime. Hence my previous question.

OK - So the rise time of the PMT is 1nS. The dwell time of my scanner is 50nS.

 

[crutschow]

OK - So the rise time of the PMT is 1nS. The dwell time of my scanner is 50nS.

Op amps with a 1nS risetime (implying a closed loop bandwidth of at least 350MHz) are not easy to find. And designing such a high speed amplifier is not for novices. I would suggest purchasing a device designed for this purpose such as one of these. It will save you a lot of grief. :wink:

 

[FvM]

A single transistor amplifier as considered in your initial post might be an option (using a fast GHz transistor). It must be however impedance matched to the circuit, both PMT output and ADC input to work with ns rise times. I can imagine, that the PMT to ADC interface is using 50 ohm impedance. In this case, the amplifier must have voltage gain.

A detailed description of the existing system is necessary. Some points in your post are hard to understand related to nanosecond signals, e.g. the 5 - 25 V output point,