OPA735: Photo diode amplifier design support

Part Number: OPA735

Tool/software:

Hi Team,

1. We are currently working on a photodiode amplifier circuit and need to measure currents in the nanoampere (nA) range for low light intensity.

I would like to know if a stability network is required for this amplifier.

Additionally, is the current op-amp sufficient for nA measurements? If not, could you suggest a suitable op-amp? Could you also recommend any application notes and provide your thoughts on enhancing this design?

 Op-amp Part Number - OPA735

Photo diode Part Number - VEMD1060X01

2. We are using an Op-amp in differential and Gain mode for Photodiode forward voltage sensing circuits. 

we need some suggestions for application notes on stability circuitry for Photodiode forward voltage sensing circuits.

We need Immediate response for your Side. Please support.

  • Srinithi,

    1. This is a somewhat unusual circuit for amplifying photodiode signals.  Normally, a transimpedance amplifier configuration is used for this purpose.  Here is a simple document explaining a transimpedance circuit operation: Transimpedance Amplifier Circuit .  I will include a much more complex document on transimpedance noise and stability below.
    2. Op amp stability problems are caused by two different cases.  
      1. Capacitance on the output of the op amp.  In your circuit the only capacitance is C1.  R5 will isolate C1 from the output of U2, so this capacitor is not a problem.
      2. Capacitance on the inverting node.  This is a common issue in transimpedance amplifiers, so if you change the configuration to transimpedance you should check this.  In a transimpedance amplifier, the photodiode is connected directly to the op amp inverting node.  Photodiodes can have significant capacitance so this can cause instability.  The problem can be easily solved by adding a feedback capacitor.  The presentations below cover this.
    3. Bottom line: your circuit looks stable, but I think you should probably switch to a transimpedance configuration.  However, I learn new configurations every day so you may have a good reason for using this configuration.  If you are new to photodiode amplification, you should check out the material below.

    10-Transimpedance and photodiode noise.pdf

    Stability - Capacitance on inverting input.pdf

    Best regards, Art