photodiode amplifier and bias current


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.

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 ( one of the recommended amplifiers is the AD8048, which it has 3.8nV/√Hz but 3.5uA of input bias current.


Unai Goyarrola