Lecture 06-Extrinsic capacitances

Lecture 06-Extrinsic capacitances - EE 214 Lecture 6 (HO#9)...

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Unformatted text preview: EE 214 Lecture 6 (HO#9) B. Murmann 1 Lecture 6 Design Example 2 Extrinsic Capacitance Boris Murmann Stanford University murmann@stanford.edu Copyright 2004 by Boris Murmann EE 214 Lecture 6 (HO#9) B. Murmann 2 Overview Reading 1.6.7 (Parasitic Elements) 7.1, 7.2.0, 7.2.1 (Miller Effect in CS Stage, only pp. 488-493) Introduction In today's lecture, we'll look at another CS amplifier design example this time with a more realistic input source that has finite resistance. Through this example, we find that we need more modeling to accurately predict the resulting pole at the gate node. Our discussion leads to a discussion of parasitic extrinsic capacitors around the MOSFET - overlap and junction capacitance. EE 214 Lecture 6 (HO#9) B. Murmann 3 Design Example 2 Given specifications DC gain=-4, I D 0.5mA R L =1k, R i =10k Maximize and estimate bandwidth R L V o 2V 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 gs i L o m i o C sR R r g s v s v s H + = = 1 1 ) || ( ) ( ) ( ) ( DC gain Frequency Dependence EE 214 Lecture 6 (HO#9) B. Murmann 4 Hand Calculation Just as in the previous design example, we know that g m r o >> A DC . Hence we simply find mS k g R g A m L m DC 4 1 4 4 = = = = In order to maximize bandwidth, we need C gs as small as possible. Again, this is the case for using up all the available current, i.e. minimum g m /I D V mA . mS I g D m 1 8 5 4 = = In order to estimate the achieved bandwidth, we can now find C gs using ? mS f g C T m gs 4 2 1 2 1 = = EE 214 Lecture 6 (HO#9) B. Murmann 5 Transit Frequency Chart 5 10 15 20 25 5 10 15 20 25 30 NMOS L=0.35um g m /I D [1/V] f T [GHz] 16GHz EE 214 Lecture 6 (HO#9) B. Murmann 6 Bandwidth Using the transit frequency chart, we find...
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This note was uploaded on 01/16/2011 for the course EE 214 taught by Professor Murmann,b during the Spring '04 term at Stanford.

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Lecture 06-Extrinsic capacitances - EE 214 Lecture 6 (HO#9)...

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