About CMRR

Hi Tokumoto-san,

Good day. The CMRR(dB) at 65C should be -20log(31.62-(-20)*10^-6) which is equal to 85.7 dB since the value at 65C should be below 90 dB based on the plot. Let me know if you have further questions. Thanks.

Regards,

Gilbeys

Hi GLADION-san,

　Thank you very much for your prompt reply!
　Your advice has helped me understand where I made a mistake in my calculations.

　 Please let me ask you two additional questions.
　　Q1) When the temperature is 5°C, the CMRR(dB) at 5℃ is calculated to be 　　　　93.3(dB) from the equations below.
　　　　Is my calculation correct?

　   Q2) From the AD8422 data sheet,the slope of the temperature characteristic of 　　　　the AD8422 CMRR(uV/V) and the AD8429 CMRR(uV) slope are opposite.
　　　　Am I correct in understanding that the temperature characteristics of CMRR 　　　　do not always degrade at the high temperature?
　　　　　*It depends on the device.

　Thank you and best regards,
　Tsuyoshi Tokumoto

Hi Tsuyoshi-san,

Good day. Yes, the CMRR you calculate for 5C is correct. The degradation of the CMRR due to temperature also depends on the part since these two parts were fabricated using different technologies. Here's an article you can use as a reference: https://www.analog.com/media/en/technical-documentation/technical-articles/25406877Common.pdf. Hope this helps.

Regards,
Gilbeys

Hi GLADION-san,

I appreciate your prompt reply and your additional information.
My question about CMRR has been cleared up.

Please let me ask you just one more question.

Page 5 of the AD8429 data sheet states, “The specified performance
temperature range is -40°C to 125°C.”
On the other hand, the specifications in the data sheet page 3 also
states, "TA = 25°C,unless otherwise noted".

Does this mean that the AD8429 has only been final tested at 25°C,
but the values on the datasheet are guaranteed by design at -40°C
to 125°C?

I’d like to ask for your advice on how I should inform my customer
about the specification values for temperature.

Thank you and best regards,
Tsuyoshi Tokumoto

Hi Tsuyoski-san,

Good day. The specs table is guaranteed by design and this value is only specified for 25C:

The CMRR vs. Temp TPC is guaranteed by bench using a representative sample and is tested through the temo -40C to 125C. Thank you.

Regards,
Gilbeys

Hi GLADION-san,

I appreciate your help.
I have understood the content of your reply.

Thank you and best regards,
Tsuyoshi Tokumoto