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Old 15th August 2006, 05:33 AM   #1
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Join Date: Sep 2005
Default Fully differential opamps and common mode voltage

Okay, let's say I have a discrete fully differential opamp, but I do NOT have any kind of common mode voltage adjust.

So that I understand the concept better ==> what could happen at the outputs with no consideration to the common mode output voltage (worst-case)?
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Old 15th August 2006, 07:13 AM   #2
Tim__x is offline Tim__x  Canada
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Join Date: Jun 2004
Location: Edmonton area, Alberta
The worst thing that I can think of happening is for both outputs to slide to one rail and stay there. This would mostly depend on the various impedances within the amplifier, any particularly high impedance nodes, like a current source loaded Vas, will be very upredictable without common mode feedback.

A common mode amplifier (and feedback path) can be very simple, just a couple transistors, you'll save a lot of trouble by adding one
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