OPA2188: how to calculate noise for an I/V circuit?

justifice zhou

Part Number: OPA2188

Hi,

I have created a I/V circuit as shown below:

I'm not sure how to calculate the noise introduced at the output of the OPAMP for VREF noise, since there is no gain for VREF, if VREF noise is 10nV, then should I just add 10nV at the output to calculate the output noise?

And to calculate the thermal noise of 2M resistor, the equation is: sqrt(4KTRΔf), but I don't know how to calculate Δf=GBP/noise gain, I know the gain bandwidth product(GBP) of OPA2188, but I don't know the noise gain of the circuit, is it 1?

Besides, are there any simulation tool that can simulate noise performance (output noise waveform)? Is TINA okay?

over 2 years ago

0 Michael Steffes over 2 years ago

Guru 48395 points

Well the transimpedance design has a peaked noise gain shape due to the detector source C, here is a full design flow discussion including noise

6787.Transimpedance design flow using high speed op amps.pptx

0 Marek Lis over 2 years ago

TI__Guru 62790 points

You may simulate the output noise by using circuit below.

However, since the stability of the circuit is a function of CJ (I picked 100pF), you must include it together with the photodiode in your simulation - see below (a minimum phase margin is 45 degrees).

Once you made sure the circuit is stable, you may simulated the noise as shown below - with Cj of 100pF and generic photodiode, the circuit shows total noise of 83uVrms.

Justifice TIA OPA188.TSC

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OPA2188: how to calculate noise for an I/V circuit?