throbscottle Well-Known Member Jan 30, 2013 #1 I'm busy trying to choose an op-amp for the input stage to my meter project - got down a few candidates! It would help if I knew how to calculate what minimum cmrr I need though. Input source is 10M divider, gain is 2.5 single sided non-inverting, I'm looking at amps with input bias currents of <10pA, load will be about 10K. Hope this is enough info for someone to start helping me! Thanks in advance
I'm busy trying to choose an op-amp for the input stage to my meter project - got down a few candidates! It would help if I knew how to calculate what minimum cmrr I need though. Input source is 10M divider, gain is 2.5 single sided non-inverting, I'm looking at amps with input bias currents of <10pA, load will be about 10K. Hope this is enough info for someone to start helping me! Thanks in advance
audioguru Well-Known Member Most Helpful Member Jan 30, 2013 #2 Your amplifier is single-ended (not differential) so the CMRR of the opamp does not affect it.
crutschow Well-Known Member Most Helpful Member Jan 31, 2013 #3 audioguru said: Your amplifier is single-ended (not differential) so the CMRR of the opamp does not affect it. Click to expand... Actually the common-mode rejection has a theoretical effect since there is a common-mode voltage equal to the input voltage with a non-inverting amp , but the CMRR of most op amps is so high that its effect on the output can be ignored.
audioguru said: Your amplifier is single-ended (not differential) so the CMRR of the opamp does not affect it. Click to expand... Actually the common-mode rejection has a theoretical effect since there is a common-mode voltage equal to the input voltage with a non-inverting amp , but the CMRR of most op amps is so high that its effect on the output can be ignored.