jonathan.wood1 Posted September 13, 2006 Report Share Posted September 13, 2006 I'm an Electrical Eng. Tech. Student and have a small question... Its a basic problem, all the information I have is,An Op-Amp has a CMMR of 76dB and an open-loop gain of 81,000.What is its common gain.. now here is my little problem.. I have the formula..Acm=(Aol/CMMR)This is I believe not correct? Since I've been getting some weird values, does this have anything to do with log20 that would get me the CMMR'?Im pretty certain thats where I've went wrong does anyone have any ideas how I can make Aol/Acm=CMMR work to give me Acm.. when I have CMMR'? Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 13, 2006 Report Share Posted September 13, 2006 80dB is a voltage gain of 10,000. 74dB is a voltage gain of 5000. So 76dB is a voltage gain of about 6000. So the common gain is 13.5. Quote Link to comment Share on other sites More sharing options...
nickagian Posted September 13, 2006 Report Share Posted September 13, 2006 Hi Electrical_tech_Student!When you use the formula Acm=(Aol/CMMR), all the quantities have to be pure numbers without dimensions (not dB), so you cannot use CMMR=76dB and Aol=81000 at the same time! You have to convert 76dB into 10^(76/20)=6300, since CMMR(in dB)=20log10CMMR. Then you can use this number with the above formula!Another solution is to convert Aol in dB and use the formula Acm(in dB)=Aol(in dB)-CMMR(in dB) and then you find Acm in dB. Quote Link to comment Share on other sites More sharing options...
jonathan.wood1 Posted September 13, 2006 Author Report Share Posted September 13, 2006 Thanks for that great help. You guys both took me in the right direction and helped me figure out how to solve these problems. Quote Link to comment Share on other sites More sharing options...
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