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# lec25 - 6.012 Electronic Devices and Circuits Lecture 25...

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Unformatted text preview: 6.012 - Electronic Devices and Circuits Lecture 25 - CMOS Scaling Rules - Outline • Announcements Handouts - Lecture Outline and Summary; on web: CMOS scaling Course evaluation - at the end of lecture today (approx. 11:45) Final - Monday, Dec. 15, 9:00 am - noon, duPont Gymnasium • Review - Intrinsic high frequency limits for transistors: w T Short-circuit current gain: best can do from CE or CS Unity gain frequency: BJT: w T 2D e /w B 2 = 2 m 2 (used Einstein rel.) e V th /w B MOSFET: w T 3 m e (V GS - V T )/2L 2 (this needs discussion) Revisiting the quasi-static assumption (^ same form; ain't it neat!!) • CMOS gate delay and power Review of Lecture 16 results: Gate Delay = 12 n L min / m n (V DD- V T ) 2 2 V DD P @max. f µ C L V DD 2 /GD = K n V DD (V DD- V T ) 2 /4 ave Power density issue: have to add this as well • CMOS scaling rules The issues and challenges Approaches: Dimension scaling Scaling voltages as well Summary of rules Clif Fonstad, 12/03 Lecture 25 - Slide 1 BJT short-circuit current gain, b j w ) sc ( b F w b : w b = g p /(C p +C m ) w t : w t @ g m /(C p +C m ) Zero, w z : w z = g m /C m Note: w z > w t >> w b (= w t / b F ) log w log |b | b F w b w t w z Low frequency value: 3dB point, Unity gain point, sc w ª g m = g m = 1 t [ C p + C m ] { g m t trB + C eb , dp + C cb , dp } { t trB + kT C eb , dp + C cb , dp ] [ qI C } In the limit of large I C : w t ( BJT ) ª 1 2 D eB = 2 m e V thermal = 2 2 t trB w B w B Clif Fonstad, 12/03 Lecture 25 - Slide 2 MOSFET short-circuit current gain, b j w ) sc ( w t : w t @ g m gs +C gd ) Zero, w z : w z = g m /C gd Note: w z > w t log w log |b | w t w z Unity gain point, /(C sc W * L 1 w ( MOSFET ) ª g m ª g m = m e C ox [ V GS- V T ] = 3 m e [ V GS- V T ] ª t 3 [ C gs + C gd ] C gs 2 WLC * 2 L 2 t trCh ox Clif Fonstad, 12/03 Lecture 25 - Slide 3 Looking more at w T for BJTs and MOSFETs: For a MOSFET we have - V T ] w ( MOSFET ) ª 3 m e [ V GS t L 2 2 [ V GS- V T ] The average E-field in the channel, E...
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lec25 - 6.012 Electronic Devices and Circuits Lecture 25...

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