Properties of common source, source follower, common gate

[wylee]

I forgot what are the important properties of these amplfiers/buffer: CMOS common source, source follower, common gate amplifier

:?: I need to know their:

1. input/output impedance (high or low)
2. what they are normally use for
3. gain & BW
4. advantage/disadvantage
5. etc...

 

[duncan94022]

Re: Properties of common source, source follower, common gat

Lots of info on the web! But briefly:

1. Common source

high input impedance, low output impedance, high gain, BW varies inversely with gain. Common voltage amplifier circuit.

2. Common gate

low input impedance, low output impedance, low gain, high BW, unity current gain. Common current regulator circuit.

3. Common drain (also called source follower)

high input impedance, low output impedance, unity voltage gain, high BW. Common voltage buffer circuit, impedance matching, simple output stage.

 

[Sprint Zagato]

Re: Properties of common source, source follower, common gat

All the 3 subblocks are very basic and you can find how to derive all the characteristics on all kind of books.

Since it's very basic, it will be used to build cascode or op..etc. So, before you can do complex analysis in further design, you have to model it as a two ports block. And thta's why you have to derive:
1. Ri
2. Ro
3. Gm -- short circuit transconductance
4. maybe voltage gain

In doing all the derivations, remember that common base or common gate has to be derived by T-model. Sometime Ro will be neglected but in Paul Gray text book they were all derived with Ro.