lecture27

lecture27 - 6.720J/3.43J - Integrated Microelectronic...

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Unformatted text preview: 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 27-1 Lecture 27 - The Long Metal-Oxide-Semiconductor Field-Effect Transistor (cont.) April 13, 2007 Contents: 1. Charge-voltage characteristics of ideal MOSFET (cont.) 2. Small-signal behavior of ideal MOSFET 3. Short-citcuit current-gain cut-off frequency, f T Reading assignment: del Alamo, Ch. 9, 9.5 (9.5.2), 9.6 Cite as: Jess del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY]. 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 27-2 Key questions What are the capacitances associated with the inversion layer charge? What is the topology of a small-signal equivalent circuit model for the MOSFET? What are the key bias and geometry dependencies of all small- signal elements in the model? How does one characterize the frequency response of a transistor? Cite as: Jess del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY]. 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 27-3 1. Charge-voltage characteristics of ideal MOSFET (cont.) Inversion charge: V DS n + n + n + p S G D B inversion layer depletion region V GS L S L D V BS For V GS > V T : L Q I = W Q i ( y ) dy 0 Change variables to V : V DS dy Q I = W Q i ( V ) dV 0 dV Cite as: Jess del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY]. 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 27-4 V DS dy Q I = W Q i ( V ) dV 0 dV From channel current equation, we have: dy W e dV | V = I D Q i ( V ) Then: Q I = W I 2 D e 0 V DS Q i 2 ( V ) dV Now use charge-control relationship: Q i ( V ) = C ox ( V GS V V T ) Finally get: 2 ( V GS V T ) 2 + ( V GS V T )( V GD V T ) + ( V GD V T ) 2 Q I = WLC ox 3 ( V GS V T ) + ( V GD V T ) Cite as: Jess del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY]. 6.720J/3.43J - Integrated Microelectronic Devices - Spring 2007 Lecture 27-5 2 ( V GS V T ) 2 + ( V GS V T )( V GD V T ) + ( V GD V T ) 2 Q I = WLC ox 3 ( V GS V T ) + ( V GD V T ) Evolution of Q I with V DS : Q I -WLC ox (V GS-V T ) V DS =V DSsat =V GS-V T V GS >V T 2 WLC ox (V GS-V T ) 3 0 0 V DS V DSsat - Used fundamental charge control relationship expression only valid in linear regime....
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lecture27 - 6.720J/3.43J - Integrated Microelectronic...

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