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# CMIR of single stage amplifier

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#### avinash

##### Full Member level 3
i have a differential stage amplifier.how to calculate the CMIR of this amplifier?

I assume CMIR is Common Mode Input Range?
For a fixed differential input vary the common mode input and plot the gain.
The gain starts to suffer beyond a certain point.

Giri

make sure all the transistors are sat

Pls upload ur schematic of differential input stage, thus CMIR can be calculated according to input transistor operating state.

Connect your amplifier in unity gain feedback configuration ( negative feedback) and sweep the positive input from the negative supply rail to the positive supply rail. The range of voltages for which the output follows the input voltage i.e. the output voltage is equal to the input voltage is your ICMR.

dear assembly ,u r absolutely wrong .the technique u r telling me is for operational amplifier whose opern loop gain is quite high.but for singal stage amplifier whose open loop gain is low cannot be used as unity gain amplifier as it does not provide virtual ground on the input.

avinash bhai,

just sweep the common mode input and check ur gain.
the range of CM which is meeting ur gain spec is ur CMIR.

PS: i think u shd be polite with assembly. he was trying to help u. avoid using the words "u r wrong". u can use better words to put ur arguments..

dear opamp741,
i think you are right.i take my words back and appologize to Mr Assembly.

dear avinash,
i think the way change your CM input while make sure all transistors working in satuation region. and then find the widest range.
wish help

common mode range by definition tells that the range of i/p voltages for which the o/p is linear.,
u can plot the i/p and output u can check the linearity region,which is u r cmir.

nagula suresh said:
common mode range by definition tells that the range of i/p voltages for which the o/p is linear.,
u can plot the i/p and output u can check the linearity region,which is u r cmir.
what is i/p and o/p

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