Common Mode Voltage

Tech Note

Theoretically, differential measurements eliminate the effects of common mode voltage. Unfortunately, all differential amplifiers have two gains; a differential gain and a common mode gain (and each acts independently). Moreover, the value of these gains depend upon how the output is connected! This newsletter expands upon the issues involved and shows that you need to be very careful in applying practical, real world semiconductor amplifiers to deal with common mode voltage problems.

You can take a much easier path - use our technology! Dataforth's isolated signal conditioners are designed with a patented isolation barrier that results in a common mode gain specification that is INDEPENDENT of the module's differential gain! Download the following application note and Excel spreadsheet to learn all about these interactions... and to experiment with your own data in a dynamic worksheet:

Dataforth's "Common Mode Voltage" Application Note (AN103 482Kb .pdf)
Interactive "Common Mode Voltage" Excel worksheet (141Kb .xls)

Remember, our Application Engineers can assist you with signal conditioner selection over the phone or via fax and email. Call Dataforth at 520-741-1404 (fax 520-741-0762) or Email us at

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