OPA627: resistor noise bandwidth

justifice zhou

Intellectual 400 points

Part Number: OPA627

Hi,

in the related post, Art Kay gives the method of calculating R1 noise and Rf noise independently.

But I find that it doesn't count for BWn.

I wonder how to calculate BWn for R1 noise and Rf noise.

For example, I think Rf noise should be able to be shown directly at the output since it's directly connected to the output, then how to calculate BWn for Rf noise?

Is it still GBW/(noise gain)? But for Rf noise whose frequency is higher than GBW/(noise gain) should still be directly passed to the output, isn't it?

over 1 year ago

0 Luis Chioye over 1 year ago

TI__Guru 55466 points

Hi Justifice,

Please find below the links for TI training on Op-Amp noise showing the calculations to analyze noise in op-amp circuits accounting for the noise bandwidth of the circuit.

Since the feedback resistor is connected across the feedback of the op-amp, the noise contribution of the feedback resistor is limited by the noise bandwidth of the op-amp circuit. If for example, you were to add a resistor in series at the output of the op-amp, after the op-amp circuit, and not in the op-amp feedback, then in that case the noise of the resistor would not be limited by the bandwidth of the amplifier.

TI Precision Labs Video Series in Op Amp Noise:

Op Amps: Spectral density

Op Amps: Calculating RMS Noise

Op Amps: Calculating total noise

Op Amp Noise: Simplifying calculations

Op Amp Noise: Noise spice simulation

Op Amp Noise: Verifying the noise model

Op Amp Noise: Measuring the system noise

Op Amp Noise: 1/F flicker noise

Op Amp Noise: Noise - Lab

The op-amp noise analysis presented has been correlated many times with bench measurements, and tested in the design of countless circuits through out the years.

Regards,

Luis

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OPA627: resistor noise bandwidth