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ADA4938 not static CMRR at low frequencies

Question asked by florianh on Feb 15, 2018
Latest reply on Feb 19, 2018 by florianh

We are reevaluating the use of the ADA4938. The CMRR is specified to be TYP: -75dB @ ∆VIN, cm = ±1 V, f = 1 MHz.

The CMRR measured on an Eval Board with ADA4938 reveals, that the CMRR is strongly frequency dependent. (red curve: ADA4938, blue: ADA4932, please disregard absolut values) :

Unfortunately the SPEC stops in the interesting regime and hints more to a static CMRR below 100kHz.

  • Could anyone explain this behaviour?
  • We could not see any tuning of this with temperature?
  • Is this resulting from Design and are the features under different conditions static?
  • Is it device to device dependent?