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The easiest way to do that is by shorting both input and apply a variable DC voltage to both throu the full range of input voltage. Monitor the output for each applied DC input.
The result of A=20*log(Vo/Vi) will be CMRR curve in dB.
The easiest way to do that is by shorting both input and apply a variable DC voltage to both throu the full range of input voltage. Monitor the output for each applied DC input.
The result of A=20*log(Vo/Vi) will be CMRR curve in dB.
I think this method will give a result of common mode gain also called Ac.
But the CMRR=Ad/Ac
How to get CMRR frequency response of a amplifer?
Added after 2 minutes:
Hughes said:
You may refer to Allen's book: "CMOS Analog Circuit Design"
You will get the best signal-to-noise ratio by measuring at the highest permissible cmv. Also, it's unnecessarily complicated to sweep the cmv and evaluate the resulting cmrr curve because it is likely that cmrr will be well represented (with the very best snr) at a single, high cmv.
So, simply apply the maximum cmv to both inputs (which should be shorted together) and measure the output, then compute the cmrr as described in earlier posts.
Can you please explain how to simulate CMRR for a fully differential op amp? I want to perform a Monte Carlo simulation and then select the worst case CMRR. How can I ensure that the simulation parameters are the same in my circuit for a given simulation run?
For a fully differntial amplifier, you need to introduce mismatches in your circuit to get meaningful CMRR results. Without mismatches, you would get an infinite CMRR ( i assume u apply a common mode signal to both inputs and measure the differntial output )
hi boooser,
When you monte-carlo on differential op-amp it gives the common-mode gain variation and mean. Do a separate simulation for differential gain (say at worst corner) and take the ratio. I guess this is a crude of doing but it gives a good estimate of worst case CMRR.
Very popular theme. But so difficult to use "search".
See attachment for example how build test bench for fully differential amplifier.
CMRR calculations are only valid for montecarlo simulation, because CMRR is strong affected by mismatch. If u haven't MC models, u'll can introduce mismatch in ur schematic (e.g. introduce voltage source with dVth in gate circuit, dVth is calculated from ur process specification as dVth=A/sqrt(W*L), constant A provided by fab) so u'll get only estimation of CMRR.
anyone could tell me is it anyway i able to get those scripts and test schematic in the white paper " Functional Verification Of A Differential Operational Amplifier" ??
thanks in advance
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