ADA4522 CMRR spec

In the datasheet rev D, CMRR is specified as 155dB typical @ 5V and 160dB for 30V operation, yet figure 30 shows it to be only 110dB from 10Hz to 100Hz, declining thereafter. Presumably the graph is in error?

Is CMRR normally specified at DC?

Parents
  • Hi, Emman, thanks for the prompt response.

    I'm sorry but I find that explanation very hard to accept. It seems to me that it would be a very unusual op-amp where the CMRR drops by 50dB from DC to 10Hz - that is a huge amount, especially given that isn't a very slow micro-power amplifier. It would be even stranger for the CMRR to then level out and remain steady up to nearly 100Hz before it starts to decline again.

    I have looked at various datasheets since and whilst most seem to be consistent, the same problem seems to apply to the ADA4528 (160dB DC, 110dB @ 100Hz in fig. 35), AD8538 (150dB DC, 108dB @ 100Hz, fig. 15)

    The AD8531 seems to suffer the opposite problem - DC CMMR spec is 47dB typical whereas fig. 22 shows it to be 86dB from 1kHz to 10kHz before it starts to drop off. Which is the correct figure?

Reply
  • Hi, Emman, thanks for the prompt response.

    I'm sorry but I find that explanation very hard to accept. It seems to me that it would be a very unusual op-amp where the CMRR drops by 50dB from DC to 10Hz - that is a huge amount, especially given that isn't a very slow micro-power amplifier. It would be even stranger for the CMRR to then level out and remain steady up to nearly 100Hz before it starts to decline again.

    I have looked at various datasheets since and whilst most seem to be consistent, the same problem seems to apply to the ADA4528 (160dB DC, 110dB @ 100Hz in fig. 35), AD8538 (150dB DC, 108dB @ 100Hz, fig. 15)

    The AD8531 seems to suffer the opposite problem - DC CMMR spec is 47dB typical whereas fig. 22 shows it to be 86dB from 1kHz to 10kHz before it starts to drop off. Which is the correct figure?

Children
No Data