Lecture 03-CS and figure of merit for transistors

Lecture 03-CS and figure of merit for transistors - Lecture...

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EE 214 Lecture 3 (HO#5) B. Murmann 1 Lecture 3 Common Source Amplifier Performance Figures of Merit for Transistors Boris Murmann Stanford University murmann@stanford.edu Copyright © 2004 by Boris Murmann
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EE 214 Lecture 3 (HO#5) B. Murmann 2 Overview Reading 1.6.8 (Transit Frequency) Introduction – Having established some basic modeling tools, we will now look at the achievable performance of our common source stage. We'll derive first order expressions for the amplifier's bandwidth and power dissipation. As we will see, these metrics are proportionally related to more fundamental performance measures of the MOS device itself: Transit Frequency and Transconductor Efficiency.
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EE 214 Lecture 3 (HO#5) B. Murmann 3 Common Source Amplifier Revisited Consider a common source stage driven by a "transducer" Ideally, what we want to achieve is – A certain voltage gain – Large bandwidth, low power dissipation I D +i d R L V O +v o V DD v i V I r o C gs g m v gs + v gs - + v o - R L R i Transducer R i v i
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EE 214 Lecture 3 (HO#5) B. Murmann 4 Transfer Function gs i L o m i o C sR R r g s v s v s H + = = 1 1 ) || ( ) ( ) ( ) ( For simplicity, let's assume that R L is fixed, and R L << r o The desired DC gain (A DC ) then dictates our choice for g m DC gain Frequency Dependence OV m D OV D m V g I V I g 2 1 2 = = Now recall that L DC m R A g =
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EE 214 Lecture 3 (HO#5) B. Murmann 5 Power Dissipation Substituting I D and g m using the expressions on the previous slide yields OV DC L DD V A R V P = 2 1 Clearly, minimizing V OV will also minimize power dissipation – Actually, how about making V OV 0? • More later… Let's now look at the bandwidth of this circuit Power dissipation is given by D DD I V P =
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EE 214 Lecture 3 (HO#5) B. Murmann 6 Bandwidth The –3dB bandwidth of our circuit is ox gs gs i dB WLC C C R 3 2 : with 1 3 = = ω OV m V L W Cox g µ = In order to make this expression more insightful, we can eliminate C ox using OV DC i L dB V L A R R = 2 3 1 2 3 It then follows that
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EE 214 Lecture 3 (HO#5) B. Murmann 7 Discussion
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Lecture 03-CS and figure of merit for transistors - Lecture...

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