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Transimpedance Amplifier

Hari T O0
Genius 3820 points

Other Parts Discussed in Thread: OPA314

Hi,

I need to design a transimpedance amplifier which should be able to conver currents in the nano ampere range.

May I know which opamp parameters need to be checked to know whether the opamp can convert the currents in the nano ampere range.

Regards

Hari

  • 0
    TI__Prodigy 610 points

    Hi Hari,

    There are tons of  good material at ti.com that treat the design of  TIAs. A good starting point is to read the three-part blog series "What Op Amp do I Need? (Transimpedance Amplifiers)" by John Caldwell. I also like this post by Collin Wells. Finally here's a TI reference design.

    There are a few things that you will typically need to care about when designing a TIA. Firstly, the diode's capacitance adds to the summing node of the amplifier and degrades the phase margin. Secondly, DC parameters such as bias current and offset voltage can be a concern. Consider that the former will also flow through the current gain resistor along with the actual signal and therefore must be significantly smaller than the signal you try to measure (a CMOS amplifier will generally be capable of that since it will be possible to find ICs with bias current lower than one pA, e.g the OPA314). Thirdly, noise from the resistors and from the amplifier should be considered to meet system requirements.


    Best of luck with your design,


    Gustaf