OPA2192: question of AC CMRR of OPA2192

chen zhe

Prodigy 75 points

Part Number: OPA2192
Other Parts Discussed in Thread: OPA192

Tool/software:

Hi team,

I use below circuit to test the CMRR of OPA2192:

however the result is different from datasheet:

datasheet shows opa2192`s CMRR can keep 140dB till 10kHz, but my test result show it drop start from 10Hz, and only 60dB@10kHz:

then I change my testing cuicuit to below:

however, the result seem the same like my first cuircuit`s result:

would you help to check why this is different from OPA2192`s datasheet？

And how dose your team get the CMRR source data of opa2192? By simulation or testing? if testing ,what test circuit do you use for it?

Thanks very much.

Zhe

Regards

1 month ago

0 chen zhe 1 month ago

Prodigy 75 points

Sorry for some error happened on result pasting, so I upload it again:

0 Raymond Zhang1 1 month ago in reply to chen zhe

TI__Guru 69891 points

Hi Che Zhe,

chen zhe said:
would you help to check why this is different from OPA2192`s datasheet？

The following test configuration refers to PSRR test specification. The AC noise is injected via power sources and it is called 电源抑制比. Your PSRR plot matches the OPA1922's datasheet, except it is named as CMRR. The OPA192 configuration shown below is defined as PSRR or 电源抑制比.

TI does the PSRR and CMRR slightly differently due to the op amp application, but the concept and theory are identical to what you configured above, see the link below.

https://e2e.ti.com/blogs_/archives/b/precisionhub/posts/dealing-with-rejection-instrumentation-amplifier-psrr-and-cmrr

chen zhe said:
And how dose your team get the CMRR source data of opa2192? By simulation or testing? if testing ,what test circuit do you use for it?

In OPA192 configuration below, it represents CMRR for the difference amplifier with gain of 5V/V. I see that you are using 50ppm precision resistor for the test, but the resistor matching will only give the CMRR at approx. 86dB range (at Gain of 1V/V). In order to obtain higher CMRR in your circuit, it is necessary to use matching resistors that is better than 50ppm. However, the increased gain in difference amplifier improves the effective CMRR, since it boosts the differential signal without increasing the common mode signal.