If I want to caculate the WCA of the Vout, which parameters should I take into account? and how to use them? Thanks.
Hello Guozhu,
From the TI precision labs presentation on Common-mode Rejection, we get a good summary of input-referred errors.
The error is the sum of input offset error, Aol error, CMRR, PSRR, and EMIRR (if data is available).
Your offset error will be your Vos, and your input bias current error (if your input impedances are matched, this becomes input offset current multiplied by your input resistance)
Your CMRR error will be your change in common mode divided by your CMRR. (Datasheet CMRR is measured at CM of 0V, so if your CM voltage is 2V, then you would divide 2V-0V by 65dB)
Your Aol error will be the change in output voltage divided by your Aol
Your PSRR will be the change in power-supply divided by your PSRR. If the power supply is changing at a specific frequency like from the ripple of a switch mode power supply, then the AC PSRR must be used (the LM2904AVQPWR-Q1 does not have AC PSRR in the typical graph section, I would recommend using LM2904BQPWRQ1 instead of LM2904AVQPWR-Q1)
EMIRR would be if there is any high-frequency noise that can couple on to the circuit. Internal EMI filters are only present on the B versions of the device.
Best,
Jerry
