h09_lecture6_2

h09_lecture6_2 - Lecture 6 Design Example 2 Extrinsic...

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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.
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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 0 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 π = =
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EE 214 Lecture 6 (HO#9) B. Murmann 5 Transit Frequency Chart 0 5 10 15 20 25 0 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 fF GHz mS f g C T m gs 40 16 4 2 1 2 1 = = = π MHz fF k C R f gs i dB 398 40 10 1 2 1 1 2 1 3 = = =
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h09_lecture6_2 - Lecture 6 Design Example 2 Extrinsic...

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