lecture37

lecture37 - 6.720J/3.43J- Integrated Microelectronic...

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Unformatted text preview: 6.720J/3.43J- Integrated Microelectronic Devices- Spring 2007 Lecture 37-1 Lecture 37- Bipolar Junction Transistor (cont.) May 7, 2007 Contents: 1. Common-emitter short-circuit current-gain cut-off fre- quency, f T Reading material: del Alamo, Ch. 11, 11.4.2 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 37-2 Key questions How is the frequency response of a transistor assessed? What determines the frequency response of an ideal BJT? How can the frequency response of a BJT be engineered? 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 37-3 1. Common-emitter short-circuit current-gain cut-off frequency, f T f T : high-frequency figure of merit for transistors Short-circuit means from the small-signal point of view. BJT is biased in FAR. I C +i c I B +i b i b I B V CE Focus on small-signal current gain: i c h 21 = | v ce =0 i b For low frequency, h 21 F , for high frequency h 21 rolls off due to capacitors. Definition of f T : frequency at which | h 21 | = 1. 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 37-4 Small-signal equivalent circuit model: C jc i c i b C +C je + - g m v be v be g i c = g m v be jC jc i b = [ g + j ( C + C je + C jc )] v be Then: g m jC jc h 21 = g + j ( C + C je + C jc ) Magnitude of h 21 : g 2 + 2 C 2 2 | h 21 | = g + 2 ( m C + C je jc + C jc ) 2 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 37-5 g 2 + 2 C 2 2 | h 21 | = g + 2 ( m C + C je jc + C jc ) 2 Bode plot of | h 21 | : log |h 21 | F c 1 T -1 log Three regimes in | h 21 | : low frequency, : | h 21 | g m = F g intermediate frequency, c : | h 21 | ( C + g C m je + C jc ) high frequency, c : C jc | h 21 | C + C je + C jc Cite as: Jess del Alamo, course materials for 6.720J Integrated Microelectronic Devices, Spring 2007....
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This note was uploaded on 09/24/2010 for the course EECS 6.720J taught by Professor Jesúsdelalamo during the Spring '07 term at MIT.

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lecture37 - 6.720J/3.43J- Integrated Microelectronic...

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