MIT6_012S09_lec10

MIT6_012S09_lec10 - Lecture 10 MOSFET (III) MOSFET...

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Lecture 10 MOSFET (III) MOSFET Equivalent Circuit Models Outline Low-frequency small-signal equivalent circuit model High-frequency small-signal equivalent circuit model Reading Assignment: Howe and Sodini; Chapter 4, Sections 4.5-4.6 6.012 Spring 2009 Lecture 10 1
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Large Signal Model for NMOS Transistor Cut-off Linear / Triode: Saturation Regimes of operation: Effect of back bias I D = 0 I D = W L μ n C ox V GS ± V DS 2 ± V T ² ³ ´ µ V DS I D = I Dsat = W 2 L n C ox V GS ± V T [ ] 2 1 + ² V DS [ ] V T ( V BS ) = V To + ± ² 2 ³ p ² V BS ²² 2 p [ ] V DS I D V GS V GS =V T V DSsat =V GS -V T 0 0 linear saturation cutoff V GS V BS V DS I D 6.012 Spring 2009 Lecture 10 2
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Small-signal device modeling Small-signal is small ± response of non-linear components becomes linear Since response is linear, lots of linear circuit techniques such as superposition can be used to determine the circuit response. Notation: i D = I D + i d ---Total = DC + Small Signal Key Points: In many applications, we are only interested in the response of the device to a small-signal applied on top of a bias. V GS V BS V DS I D +i d v gs v bs v ds + - + + - - 6.012 Spring 2009 Lecture 10 3
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Mathematically: With i d linear on small-signal drives: i D ( V GS , V DS , V BS ; v gs , v ds , v bs ) ± I D V , V , V ( ) + i d ( v , v , v ) i d = g m v gs + g o v ds + g mb v bs De ne: g m ± transconductance [S] g o ± output or drain conductance [S] g
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MIT6_012S09_lec10 - Lecture 10 MOSFET (III) MOSFET...

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