- #1
Ianlamb
- 4
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Member advised to use the homework template for posts in the homework sections of PF.
Hi,
I have this question.
An instrumentation measuring system uses a differential amplifier having a CMRR of 120 dB and differential gain of 105. The maximum differential input signal is 60 μV. If the amplified noise voltage is specified to be not more than 1% of the maximum output voltage, calculate the maximum common mode voltage that can be present in the input to the amplifier.
Just need to know if this is correct or I am on the right track.
I have the formula
CMRR=20log10(Adiff/Acm)
Then
120=20log10(10^5/Acm)
Then
120/20=log10(10^5/Acm)
Then
6=log10(10^5/Acm)
Then taking anti logs
1000000=10^5/Acm
Transpose this into
Acm=10^5/1000000=0.1volt
Is this correct? as when I plug the 0.1 back into the original equation I do not get the original 120dB answer.
Thanks.
I have this question.
An instrumentation measuring system uses a differential amplifier having a CMRR of 120 dB and differential gain of 105. The maximum differential input signal is 60 μV. If the amplified noise voltage is specified to be not more than 1% of the maximum output voltage, calculate the maximum common mode voltage that can be present in the input to the amplifier.
Just need to know if this is correct or I am on the right track.
I have the formula
CMRR=20log10(Adiff/Acm)
Then
120=20log10(10^5/Acm)
Then
120/20=log10(10^5/Acm)
Then
6=log10(10^5/Acm)
Then taking anti logs
1000000=10^5/Acm
Transpose this into
Acm=10^5/1000000=0.1volt
Is this correct? as when I plug the 0.1 back into the original equation I do not get the original 120dB answer.
Thanks.