Hello, I'm studying the MOS/BJT differential pair on Microelectronics by Sedra-Smith.(adsbygoogle = window.adsbygoogle || []).push({});

The book refers to voltage signals with the following notations:

= DC voltage

= AC voltage

= generic time-varying voltage

When it comes to differential pairs, it uses a quite confusing notation for differential inputs: they are always called , like they could be only AC signals, but I'm not positive on this restriction.

I happened to find some exercises on the MOS differential pair based on Sedra-Smith's figures (link) and they seem to confirm that may be both a DC and an AC signal. Is this definitely correct?

If it is, I have a second question: what would be the point of applying a DC differential input to a differential pair? I mean, is there any application in the real life in which a DC voltage needs to be amplified?

Thanks in advance for your help.

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# Differential pair: is the differential input always supposed to be an AC voltage?

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