• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 47 subscribers
  • Views 485 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Transimpedance amplifier with OPA657

Thomas 11
Prodigy 120 points
Other Parts Discussed in Thread: OPA657, LM317

Dear All,

I tried to build a transimpedance amp with the opamp I have (OPA657). The circuit is made connecting all pin connections in the air.

I believe that with no breadboard will make less noisier in the circuit. I take 5V from LDO (LM317).

The problem is even with no photodetector, the amplifier output has 50mV p-p output.

I am expecting very low noise as there is no sensor yet.

I must have very low noise at the amp as the signal from the PD is very weak like 50nA.

With this noise is I won't be able to see the signal.

How can I improve the noise at the amp output and what could be the source of the noise?

The circuit schematic and all noise measurements are shown in the figure.

Thanks,

Thomas

  • 0
    TI__Expert 4115 points

    Thomas,

    I assume you followed design as shown in the data sheet. If so, stability of the circuit depends on having the capacitive load of the photo diode in the circuit. Without it, the OPA657 will most likely oscillate and that could be the noise you see. Try to put 20pF capacitor to ground on negative input. This will put device in noise gain of 20 at high freqeuncy and should compensate so it will not oscillate.