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photodiode amplifier and bias current

Question asked by Unai on Nov 5, 2013
Latest reply on Nov 6, 2013 by Matt.Duff

Hello,

I have to measure the current of a photodiode.

Input signal is:

  • Maximum current 15uA.
  • Frequency of the pulsed current 4MHz
  • Photodiode capacitance: 1pF

I have done the desing using the AD8067.

photodiode amplifier.jpg

I have obteined good results, but i need to improve the SNR. The source of noise is the input voltage noise, so i have been looking for opamps with lower values. The AD8067 has 6.6nV/√Hz, and i have found the ADA4897-1 which it has only 1nV/√Hz. The problem is that the maximum input bias current is -17uA. How does it affect? is there any way of overriding it?

 

In the analog photodiode wizard (http://www.analog.com/designtools/en/photodiode/#/photoDiode) one of the recommended amplifiers is the AD8048, which it has 3.8nV/√Hz but 3.5uA of input bias current.

 

Thanks

Unai Goyarrola

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