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OPA836 TINAspice vs Experimental

Other Parts Discussed in Thread: OPA836

Hi,


I used TinaSPICE to simulated the OPA836 as an Transimpedance Amplifier (schematic attached). IG1 is a square wave [0 250µA] and is currently working at 5MHz. IG1 D1, R4 and R6 gather are a photodiode model. Dynamics results of the simulation match with the experimental results only if the R1 resistor is present. Why?


In other words, when R1 resistor is removed from the simulation and the experimental setup, both results do not match. If I add the R1 resistor in both simulation and experimental setup, both results match.
Is there any specification why R1 should be connected between the ground and the In+ input?

Thank you for taking time.

Steven

  • How do the results differ without the resistor? 

    It is possible that the reverse leakage current of the diode is poorly modeled and the resistor swamps out it's impact.  

    Ideal current sources can also cause problems, the 1M resistor would help with that.