Transimpedance amp design with OPA2846

Thomas 11

Other Parts Discussed in Thread: OPA2846

Hi All,

I am designing the transimpedance amplifier circuit using OPA2846. There is an example for a two-stage amplifier in the data sheet.

The example is for 100k ohm transimpedance amplification. But my signal is very weak around 50nA.

So I need 8M ohm transimpedance gain. I design 200k ohm in the first stage and the second stage gain is 40.

Is the opamp suitable for this amplification? Will the opamp be a stable opamp for this application?

The circuit is as shown below.

Thanks,

Thomas

over 13 years ago

0 Bart Stiller over 13 years ago

TI__Expert 5400 points

Thomas,

I believe this circuit will be ok from a stability standpoint. A few notes:

To maintain a DC level of 2.5V, the capacitor C5 should be larger, at least 1uF. Also note that the divider network at each noninverting terminal should be based on twice the feedback resistance, ie R4 and R5 = 400k; R11 and R12 = 20k.

You might also consider using smaller resistor values in the second stage, perhaps Rg = 50ohms and Rf = 2kohms.

0 Thomas 11 over 13 years ago in reply to Bart Stiller

Prodigy 120 points

Thanks Bart.

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Transimpedance amp design with OPA2846