OPA1612: Current noise

Remy HOFF

Part Number: OPA1612
Other Parts Discussed in Thread: OPA1611

Hi all,

i am working on a high end amplifier and would like to use OPA1612 as state of the art.

I am thinking about the current input noise which can be carefuly calculated as the source resistance involve more noise.

My topology implement a OPA1612 in inverter manner with a potentiometer before it as a voltage divisor and it is hard for me to understand if it adds a source resistance or not ...

My pot is 10k and i try to know if it will add input current noise more to the classical R1 and R2 which define the overall gain, depending of course of the position of the pot.

Thank you very much for your help.

over 3 years ago

0 Raymond Zhang1 over 3 years ago

TI__Mastermind 48076 points

Hi Remy,

Is the following current noise circuit is what you described?

Anyway, enclosed is the model in the above simulation. Also, I included the video clip for the noise simulation.

/cfs-file/__key/communityserver-discussions-components-files/6/OPA1611_2D00_2-current-noise-11062020A.TSC

https://training.ti.com/ti-precision-labs-op-amps-noise-verifying-noise-model?context=1139747-1139745-14685-1138803-13844

If you have additional questions, please let us know.

Best,

Raymond

0 Remy HOFF over 3 years ago in reply to Raymond Zhang1

Prodigy 230 points

Hi Raymond,

amazing tool. I never tested Tina with op amp model.

I ran several resistances values and found a good results with R4=500 et R1=750 ohm (gain of 1.5 needed) in terms of total voltage noise.

I also found that R3 (Rbias to cancel input voltage offset) add noises ... Then better results with 0.

However, small feedback cap degrades the THD (1kHz Fourrier analysis). With cap=0, THD is 0.00025%. With 500pF, THD is 0.009%. With 1nF, THD is 0.02%.

Because this cap is needed for stability, my feeling is that there is a dream to have the lower noise but we need a higher cap to achieve the pole gain for a given frequency, which degrade a lot the THD.

Between THD and Noise, the THD is the predominant factor, due to the cap.

What is your feeling ?

0 Raymond Zhang1 over 3 years ago in reply to Remy HOFF

TI__Mastermind 48076 points

Hi Remy,

It sounds about right. Please also check the total noise of the circuit. OPA1611 is high BW op amp.. You do need C1 capacitor to lower the broadband noise of the OPA1611. Also please check the these parameters after a circuit is built.

Best,

Raymond

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OPA1612: Current noise