Hello, If you go to this link: http://en.wikipedia.org/wiki/Common-mode_rejection_ratio and scroll all the way down to the bottom where they show the: "Example: operational amplifiers" section.... we have: I get +/-222mv ???? Am I doing the math wrong?
90/10 then the result is multiplied by 10. then 10/the result above hence: 10/((90/20)10) = 0.222??? and they get 316 micro volts?
I think there are several issues with the way you are trying to solve this. First remember that for voltage ratios, the equation is dB = 20log(ratio). So for this problem, you start with 90dB = 20log(10/x). To solve that equation, you divide both sides by 20, and then take 10^ for both sides. Can you take it from there...?
Hi berkeman, You talking to a very slow guy here!!! so I try: I went back to my algebra notes of 20 years ago and saw the example: 2 = log(base10)(100) then I tried doing the reverse: 10^2 = 100 So then I understood that its 10 to the power of (90/20)... So I did the same while following your instructions.... 90dB = 20log(10/x) 90dB/20 = (20log(10/x))/20 4.5dB = log(10/x) Antilog = 10^4.5 so: 10^4.5 = 10/x which becomes: 10/31622.8 = x 316 uV Thankyou for your help!