h13_lecture9_2

h13_lecture9_2 - Lecture 9 Common Drain Stage (Source...

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EE 214 Lecture 9 (HO#13) B. Murmann 1 Lecture 9 Common Drain Stage (Source Follower) Boris Murmann Stanford University murmann@stanford.edu Copyright © 2004 by Boris Murmann EE 214 Lecture 9 (HO#13) B. Murmann 2 Overview Reading – 3.3.7 (Common Drain Stage) – 7.2.2 (Frequency Response of Voltage Buffers) – 5.3 (Source Follower as an Output Stage, optional) Introduction – Last lecture, we have seen that a common gate stage has a fairly low input impedance, and high output impedance. The common drain stage that we'll analyze today exhibits the exact opposite features: High input impedance and low output impedance. After an analysis of relevant port characteristics, we will discuss some potential applications and also drawbacks of this circuit.
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EE 214 Lecture 9 (HO#13) B. Murmann 3 Common Drain Stage I B R L V i V DD C L V o v o g m v gs + v gs - C gd +C gb r o C gs C sb +C L R L v i -g mb v o EE 214 Lecture 9 (HO#13) B. Murmann 4 CD Voltage Transfer (1) Ltot Ltot gs m gs m i o R sC sC g sC g v v 1 + + + + = () 0 1 = + + o i m gs i Ltot gs Ltot o v v g sC v R sC sC v v o g m v gs + v gs - C gd +C gb C gs C Ltot R Ltot v i Ltot m Ltot gs m gs Ltot m m i o R g C C s g sC R g g v v 1 1 1 1 + + + + + = o mb L Ltot sb L Ltot r || g || R R C C C 1 = + =
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EE 214 Lecture 9 (HO#13) B. Murmann 5 Low Frequency Gain Interesting cases –R L →∞ , r o →∞ , g mb =0 • PMOS, source tied to body, ideal current source Ltot m m v R g g a 1 0 + = o mb L Ltot r || g || R R 1 = 1 0 = v a mb m m v g g g a + = 0 L →∞ , r o →∞ , g mb 0 • NMOS, ideal current source) (typically 0.8) –r o →∞ , g mb =0, R L finite • PMOS, source tied to body, load resistor L m m v R g g a 1 0 + = EE 214 Lecture 9 (HO#13) B. Murmann 6 High Frequency Gain Three scenarios () p s z s a v v s a v i o v
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h13_lecture9_2 - Lecture 9 Common Drain Stage (Source...

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