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Unformatted text preview: 6.720J/3.43J  Integrated Microelectronic Devices  Spring 2007 Lecture 271 Lecture 27  The Long MetalOxideSemiconductor FieldEffect Transistor (cont.) April 13, 2007 Contents: 1. Chargevoltage characteristics of ideal MOSFET (cont.) 2. Smallsignal behavior of ideal MOSFET 3. Shortcitcuit currentgain cutoff 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 272 Key questions What are the capacitances associated with the inversion layer charge? What is the topology of a smallsignal 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 273 1. Chargevoltage 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 274 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 chargecontrol 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 275 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 GSV T ) V DS =V DSsat =V GSV T V GS >V T 2 WLC ox (V GSV T ) 3 0 0 V DS V DSsat  Used fundamental charge control relationship expression only valid in linear regime....
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 Spring '07
 JesúsdelAlamo
 Transistor, Volt

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