LMH6642: Photo-Diode Current-to-Voltage Conversion

Hi Elisha, 

The customer may not need to use a circuit as complicated as the one shown in figure 3 to achieve a transimpedance circuit. 500uA is an easy input current to design for and the minimum current resolution will depend on the noise of the circuit. What speed and output voltage do they need from the circuit? Also, do they know the input capacitance of their photodiode? 

Regards, 

Thanks, Jacob. I'll direct the customer to this thread to answer your questions for a quicker resolution

Dear Jacob,
I am using the above circuit but in photovoltaic mode i.e. bias voltage is zero. The resistance and capacitance are exactly as shown in the figure. The load resistance is zero since i am measuring in current mode. We are measuring the cloud coverage and we would like to record the current every second, through DAQ. I need to have 1 micro ampere resolution.

Kindly let me know if more information is required.

Warm regards,

Shweta Pal 

Hi Shweta, 

In your above diagram, can you tell me the model number of the diode you are using represented by PD? That diode will have its own parasitic capacitance that will effect the transimpedance design calculations. 

Thank you, 

Yea Shweta, 

What you draw looks like a standard transimpedance design if you are driving into the inverting summing junction of an op amp. If you are looking at clouds, unlikely you need the speed of the LMH6642. 

Normally, you would use a decompensated VFA for this type of app. Look at the LMP7717 or perhaps the OPA228. 

Touched on these transimpedance design issues towards the end of this recent article, 

https://www.planetanalog.com/author.asp?section_id=3404&doc_id=565165&

Dear Jacob,

The photodiode is by thorlabs and the product code is FDS010 .

Thank you.

Regards,

Shweta Pal.

Dear Michael,

I am sorry I am unable to understand which diagram you are referring to.

Warm regards,

Shweta Pal.