llbaobao
Member level 3
I found in Allen's book, there is a kind of method to measure the CMRR of op amp.
Please see the attached file for circuit sturcture.
there are two sequent steps:
1.set VHH to VHH+1 and VLL to VLL+1 and Vout to 1V by applying -1V to the input designated as -Vout. This is equivalent to applying a common mode input signal of 1V to the amp with mormal supply values. the value at Voff is measured and designated as voff1.
2.set VHH to VHH-1 and VLL to VLL-1 and Vout to -1V by applying 1V to the input designated as -Vout. the value at Voff is measured and designated as voff2.
then CMRR=2000/[Voff1-Voff2]
Can some of give help about how the final expression of CMRR is got?
I calculated by hand but can not get it.
Thank you for your help.
Please see the attached file for circuit sturcture.
there are two sequent steps:
1.set VHH to VHH+1 and VLL to VLL+1 and Vout to 1V by applying -1V to the input designated as -Vout. This is equivalent to applying a common mode input signal of 1V to the amp with mormal supply values. the value at Voff is measured and designated as voff1.
2.set VHH to VHH-1 and VLL to VLL-1 and Vout to -1V by applying 1V to the input designated as -Vout. the value at Voff is measured and designated as voff2.
then CMRR=2000/[Voff1-Voff2]
Can some of give help about how the final expression of CMRR is got?
I calculated by hand but can not get it.
Thank you for your help.