mudball Posted March 13, 2006 Report Share Posted March 13, 2006 hey guys... i just wanna know the meaning of what common-mode is and common- mode rejection... do these relate to each other???thx Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 13, 2006 Report Share Posted March 13, 2006 Hi Mudhall,Welcome to our forum. ;DCommon-mode signals to an opamp are signals that are the same at both inputs. The range of common mode signals for most opamps is within a few volts from each supply voltage. A few opamps like the LM324 and LM358 have inputs with a common mode voltage range that includes the negative supply, which sometimes is the circuit's ground. A feww opamps have an input common mode range that includes the positive supply voltage. New Cmos opamps have an input common mode voltage range that includes all its voltages and are called input rail-to-rail.An opamp is supposed to have differential inputs and therefore amplify only the difference between its inputs, but the inputs are not perfect and amplify common mode signals a little, and more at higher frequencies. The amount of rejection is called input common mode rejection. Quote Link to comment Share on other sites More sharing options...
Enac Posted March 16, 2006 Report Share Posted March 16, 2006 Hi Mudhall,Welcome to our forum. ;DCommon-mode signals to an opamp are signals that are the same at both inputs. The range of common mode signals for most opamps is within a few volts from each supply voltage. A few opamps like the LM324 and LM358 have inputs with a common mode voltage range that includes the negative supply, which sometimes is the circuit's ground. A feww opamps have an input common mode range that includes the positive supply voltage. New Cmos opamps have an input common mode voltage range that includes all its voltages and are called input rail-to-rail.An opamp is supposed to have differential inputs and therefore amplify only the difference between its inputs, but the inputs are not perfect and amplify common mode signals a little, and more at higher frequencies. The amount of rejection is called input common mode rejection.Great explanation, AG! Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 16, 2006 Report Share Posted March 16, 2006 Hi Ron,It is about time that you came over to this web-forum. ;D Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted March 26, 2006 Report Share Posted March 26, 2006 Also, noise can appear common mode at the inputs. There is also input capacitance which, if the noise is a higher frequency than the wanted signal, can aid in removing the noise. Quote Link to comment Share on other sites More sharing options...
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