CMRR and PSRR

[joniengr081]

I was reading the datasheet of INA240. I am always bit confuse of these two terms. Common Mode Rejection Ratio (CMRR) and Power Supply Rejection Ratio (PSRR). These are the two important characteristics of operational amplifier.

The datasheet describe CMRR as:
132-dB DC CMRR
93-dB AC CMRR at 50 kHz

And PSRR as
+/-10 μV/V

What does these two parameters means ?
What is Vcm (common mode input voltage) of an op-amp ? In the datasheet it says - 4 V to 80 V. Does it means that the Vin+ - Vin- can be maximum up to 80 V ?

[TimFox]

Last question first:  the CM range on the input voltage is for both of them together.  Your difference (V₊ - V_-) is the differential input voltage, and may not be so large as the CM range.
General answer:  if you have any two voltages V₁ and V₂ with respect to a common reference node (e.g., ground or the negative supply voltage, as relevant), you can always define the common-mode and differential voltages
V_CM = (V₁ + V₂)/2 for the common-mode, and
V_diff = (V₁ - V₂)

The rejection ratios:  if you apply an unwanted signal to either the common mode (at the input) or the power supply (difference between the two power voltages), that unwanted variation will induce an error voltage at the input, equivalent to an offset voltage.
The rejection ratio is the ratio between the (large) unwanted signal and the (small) offset voltage.
Note that the offset voltage here is an equivalent voltage at the input that would give you the measured output voltage.

[Terry Bites]

You may find this note from Renesas helpful.
It explains the effects of these parameters and how they are measured.

[MathWizard]

I've been aware of this stuff for a while, but I've never tried to measure CMRR or PSRR, those test circuits sure are easy, I better read about PSRR again. I thought it would be about AC signals, and output ripple, for some AC added on-top/between the DC rails.

For a while I've been wanting to make a test jig for various op-amp parameters. So I better choose a few circuits and just make them.