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Old 15th August 2007, 08:20 AM   #1
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Default Differential to differential amplifier

Hello everyone,
I'm working on something wich require a differential to differential amplifier. I do not want to use op amps for this, only discrete components.

I have tried to use various versions of the common long tailed pair, but the high gain causes it to behave like a comparator. Normally you loop back a portion of the output to one of the inputs (i.e. feedback), can I still do this if I need both inputs and outputs?

Any help would be most appreciated.
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Old 15th August 2007, 08:26 AM   #2
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Yes. You can use feedback from one output to an input, as well as from the other output to the other input. Both input signals then go to each input through a resistor, to be summed at the actual input point with the feedback signal.

Seems to me you need a sim to play with. Thry downloading SWCAD III, everybody here seems to use it. It's free.

Another smart move would be to study the internal diagram of a diff-to-diff opamp datasheet like the OPA1632.

Jan Didden
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Old 15th August 2007, 08:35 AM   #3
tbr is offline tbr  Switzerland
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I would have a closer look at Nelson Pass' stuff...
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Old 15th August 2007, 08:39 AM   #4
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Quote:
Originally posted by tbr
I would have a closer look at Nelson Pass' stuff...

Of course. And Erno Borbely's.

Jan Didden
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