Differential to differential amplifier

[Cauhtemoc]

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.

[janneman]

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

[tbr]

I would have a closer look at Nelson Pass' stuff...

[janneman]

Originally posted by tbr
I would have a closer look at Nelson Pass' stuff...

Of course. And Erno Borbely's.

Jan Didden