# Current to voltage covertion circuit design

1. Oct 9, 2012

### prth0901

Hi everyone. I need small help regarding my BE project. I would like to design a current to voltage converter circuit for silicon detector, which produces current of 10pA. can any one help me how to start please.

Best Regards,
nani

2. Oct 9, 2012

### davenn

Hi There Nani
Welcome to PF :)

What research have you done so far into design methods ?
We wont spoonfeed you with circuit diagrams, but if you find some circuits then you can ask questions about anything you dont understand, or improvements etc
If you are doing a BE then you must already have some ideas on how such a system operates ?

cheers
Dave

3. Oct 9, 2012

### yungman

For this, look into electronmeter amplifier. They are mostly transimpedance amplifiers.

go to Analog Devices page and look for op-amp with low bias current in 200fA max. Look for application notes and study it. This is a bigger subject than you might think and it is impractical to explain in a post. Do some study and we can talk a lot more on the requirements you need.

If you have more specific question, post back. Get some knowledge first.

4. Oct 11, 2012

### prth0901

Hi
During the study i have found this op amp (LTC6079CGN#PBF). It has input bias current of 1pA. I am attaching my circuit diagram and link. Can some one please check and give me some suggestions (http://www.farnell.com/datasheets/62514.pdf).

Regards,
Nani.

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• ###### PHOTODIODE AMPLIFIER.png
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5. Oct 11, 2012

### yungman

1pA bias current is high for OP. He/she need to detect 10pA. The feedback resistor is in the range of 1GΩ to get 10mV from 10pA. Here are threads that I had discussion on this topic:

For this low current, it is not that simple anymore. Vibration can be a big problem on top of noise, offset, drift and settling. OP has to study up electronmeter amplifier before any meaningful discussion.

Last edited: Oct 11, 2012
6. Oct 15, 2012

### prth0901

Hi yungman. My teacher suggest me to use TL072IN op amp. Now i want to simulate this circuit in mindi or Ltspice but i couldn't able to find any predefined model. I have tried in internet, I found this link (http://www.madlabo.com/mad/edat/spice/model/opamp/Tl072.mod [Broken]).

Last edited by a moderator: May 6, 2017
7. Oct 15, 2012

### yungman

You need to clarify your first post. You said you want to detect 10pA. Input bias current of TL072 is over 65pA and offset current is high. If you truly want to read 10pA with any accuracy, you cannot use this. Not even close. You need to specify more on what are you trying to read. Specification like:

1) What is the full scale ( Maximum) current you need to read?
2) What is the lowest current you need to read?
3) What is the accuracy requirement?

8. Oct 15, 2012

### Studiot

You say that your detector produces a current of 10 pA. Is this a range with 10pA the max or what? Are we really talking measuring charge or current ie can the detector produce 10pA or whatever continuously?

@yungman BTW I believe it is electrometer (without the n) which was originally a type of valve.