What do the things like Vss, Vcc, and Vdd stand for?

I know that Vss is ground, but what do the others mean? I now there are more than just the three i mentioned, so what do some of them mean (Vin, etc)?

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Apparently these terms originated from the terminals of transistors (C = collector, E = emeitter for BJTs; D = drain, S = source for FETs). Commonly Vcc or Vdd is the positive supply and Vee or Vss is the negative supply (not necesseraly the ground). And Vin is the input voltage of a device, Vo is the output, ...

 

Some of them are from transistor terminology.

Bias voltage is typically labeled Vcc or Vdd, meaning voltage on the collector (bjt) or drain (fet), respectively. Vee and Vss would mean voltage on the emitter and source, respectively. Common emitter/source would mean tied to ground, but not always - it's whatever is used as the return for the negative bias. Op Amps, for example, can have +15V on Vcc and -15V on Vee.

 

FETs:
Vdd= drain
Vss = source

BJTs:
Vcc= collector
Vee= emitter

Also note that the polarities of the N and P type FETs and BJTs are opposite (drain/source and collector/emitter). Normally when it's a uC or something like that though, the Vdd and Vss polarity seems to be referenced to the N-type devices rather than the P-types (so Vdd>Vss and Vcc>Vee).

 

Huh? I am sorry, i don't follow...

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For an NPN BJT and NMOS,

Positive is Vcc/Vdd
Negative is Vee/Vss

But for a PNP and PMOS,

Positive is Vee/Vss
Negative is Vcc/Vdd

So they have two meanings as far as polarity goes depending on what transistor you are talking about. But in an IC, they sometiems just label the power terminals Vdd/Vss or Vee/Vcc. When they do this they are using the N devices as a reference for the polarity of the power pins. Don't worry about it. You probably already know it and I'm just saying it out loud.

 

Um... ok...

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What about CMOS where the positive and negitive both go to the source?

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Vdd is assumed to be the positive rail and Vss the negative one. These are just conventional symbols, of course.

 

That's what I mean when I say for ICs, it's referenced to the N-type conventions.