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wylee
Joined: 17 Feb 2004
Posts: 113
Helped: 5
Location: Malaysia
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 21 Sep 2004 14:28 Properties of common source, source follower, common gate |
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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...
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duncan94022
Joined: 08 May 2004
Posts: 42
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21 Sep 2004 20:00 Re: Properties of common source, source follower, common gat |
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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.
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Sprint Zagato
Joined: 23 Oct 2003
Posts: 7
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27 Sep 2004 8:34 Re: Properties of common source, source follower, common gat |
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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.
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