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OPA320: Input offset voltage

Danilo A.
Mastermind 24705 points
Part Number: OPA320
Other Parts Discussed in Thread: OPA192, , OPA392

Hi Team,

We would like to ask your help regarding the customer's inquiry below.


I have a few technical questions about the OPA320S and OPA192. I have a test setup using the OPA320S that is configured as a unity-gain buffer.  I see a 500uV change in the input offset voltage when there is high frequency noise in the GND. However, I don't see the same issue with the OPA192.  I'm trying to get an understanding as to why this is occurring with the OPA320S. Based on the datasheet specifications, the OPA192 and OPA320S have similar CMRR and PSRR performance vs frequency, how the offset voltage is affected in these analog amplifiers.

Regards,

Danilo

  • 0
    Guru 140200 points

    Hi Danilo,

    the OPA320 has a higher bandwidth (20MHz) compared to the OPA192 (10MHz). This makes the OPA320 more susceptible to HF noise.

    But how is the HF noise entering GND in your test circuit? Simply injecting noise into GND would not necessarily increase the noise at the inputs of OPAmp. There most be more going on in the test setup. Can you show a schematic and a photo of your test setup?

    The usual way of dealing with HF noise would be the use of low pass filtering at the inputs and outputs of OPAmp, combined with a proper supply voltage decoupling and -if necessary- shielding measures. Unwanted HF must never reach the OPAmp Relaxed

    Kai

  • 0
    TI__Mastermind 47716 points

    Hi Danilo,

    As Kai pointed out, it is difficult to explain what is going on with 500uV offset for OPA320S' buffer configuration with a circuit schematic etc.. Yes, OPA192 has much lower in Vos specification vs. OPA320S, and it may be a part of the reason.  If you want to send us the schematic, we can take a look at it.  

    I am enclosing another OPA392 op amp which is comparable to OPA320S and low voltage precision op amp. OPA192 is considered higher voltage op amp in comparisons, and it seems that it may work for your application as well. 

    Best,

    Raymond