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04/24/07 10:43
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 		 #137874 - Calculation of Offset due to common mode voltage
Responding to: ???'s previous message
I got the answer for Offset calculation and i am interested in putting it here to be useful for any newbie who refer this thread.

If CMRR = 85dB and Common mode Voltage is 1V, then

using the formula for CMRR we get,

20 log ( Ad / Ac) = 85db
Solving the above gives (Ad / Ac) = 17783.

So, Offset Voltage = Common Mode Voltage / CMRR = 1 / 17783 = 56.2uA.
Therefore if the OPamp circuit has a gain of 10, then an offset voltage of 562µV will appear at the output.

And, this is also well formulated in the link given by Steve.

Thanks everyone for your kind help.

regard's
Suresh.

List of 72 messages in thread
TopicAuthorDate
Understanding OpAmp Circuits.            01/01/70 00:00      
   start with the basics ...            01/01/70 00:00      
   Historical aspect            01/01/70 00:00      
   Current directions            01/01/70 00:00      
      Maybe that's his confusion.            01/01/70 00:00      
         picky, picky,            01/01/70 00:00      
            Conventional Current Flow            01/01/70 00:00      
               But WHAT is flowing?            01/01/70 00:00      
                  Please elaborate.            01/01/70 00:00      
                     The >cause< is flowing...            01/01/70 00:00      
                        A suggestion.            01/01/70 00:00      
                           What do you think?            01/01/70 00:00      
                              capacitors            01/01/70 00:00      
               I see            01/01/70 00:00      
                  Its much clear now.            01/01/70 00:00      
                     Some answers...            01/01/70 00:00      
                        reply to Answers...            01/01/70 00:00      
                           Figure 9            01/01/70 00:00      
                              It helped me finding out the answers...            01/01/70 00:00      
                                 It's there...            01/01/70 00:00      
                                    Just liked to make it clear..            01/01/70 00:00      
                                       How I would design it            01/01/70 00:00      
                                          if my load is resistive ...            01/01/70 00:00      
                                             Datasheet is a bit incomplete            01/01/70 00:00      
                                                clear till now...            01/01/70 00:00      
                                                if input is current? then output??            01/01/70 00:00      
                                                   Current to voltage converter            01/01/70 00:00      
                                                      Hhm...            01/01/70 00:00      
                                                         I stand corrected            01/01/70 00:00      
                                                   Mechanism of negative feed back            01/01/70 00:00      
                                                      Thank You!            01/01/70 00:00      
                                                         A bit more details are needed            01/01/70 00:00      
                                                            Not for Application. Just learning.            01/01/70 00:00      
                                                               Answers            01/01/70 00:00      
                                                                  gain calculation??            01/01/70 00:00      
                                                                     Compensation Techniques...            01/01/70 00:00      
                                                                        Answers III            01/01/70 00:00      
                                                                           ...            01/01/70 00:00      
                                                                           Offset nulling in low cost OpAmps..            01/01/70 00:00      
                                                                              nulling an LM358?            01/01/70 00:00      
                                                                                 Opamps with Offset null pins?            01/01/70 00:00      
                                                                                    CMRR            01/01/70 00:00      
                                                                                       Let me consider an example..            01/01/70 00:00      
                                                                                          link            01/01/70 00:00      
                                                                                             Thank you.            01/01/70 00:00      
                                                                                       start with the definition and go from there            01/01/70 00:00      
                                                                                          whether offset can be calculated using a formula.            01/01/70 00:00      
                                                                                             Calculation of Offset due to common mode voltage            01/01/70 00:00      
                                                                                                Exactly !            01/01/70 00:00      
                                                                                                   But to be true i got help from a person and...            01/01/70 00:00      
                                                                     Answers II            01/01/70 00:00      
                                                                        corrected circuit of Instrumentation Amplifier            01/01/70 00:00      
                                                                           Gain is still 19!            01/01/70 00:00      
                                                                              regarding 2K & CMRR            01/01/70 00:00      
                                                                                 Sources and Solutions            01/01/70 00:00      
                                                                                 The idea of having a common ground...            01/01/70 00:00      
                                                                  VREF            01/01/70 00:00      
   It is quite simple...            01/01/70 00:00      
   op-amp golden rules            01/01/70 00:00      
      First things first:            01/01/70 00:00      
         Always??            01/01/70 00:00      
      an addition            01/01/70 00:00      
         That's not really op-amp specific.            01/01/70 00:00      
            true, the interesting fact here is            01/01/70 00:00      
         Hardly...            01/01/70 00:00      
            I've done it            01/01/70 00:00      
               Do you remember which one?            01/01/70 00:00      
                  not really            01/01/70 00:00      
                     Although most OPamp can withstand shorts...            01/01/70 00:00      
   Op-Amp Simulator            01/01/70 00:00      
      cant run 16 bit windows program :(            01/01/70 00:00      
         Try LT Spice            01/01/70 00:00      

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