4902_C2009_Studio_5_short.ppt

4902_C2009_Studio_5_short.ppt - Studio 5 Review Current...

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1 Studio 5 Review Current Source Active Load Bandwidth of Common Source Amplifier
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2 Current source Ideal goal Small signal model: Open circuit “R D =
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3 Realizing current source: MOSFET Large signal nonideality: "Compliance range" Looks like current source only for V DS >V GS -V TH V DS = V GS - V TH SATURATION
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4 MOSFET I D -V DS characteristic for fixed V GS Small-signal nonideality: slope in active region V DS = V GS - V TH
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5 Modify small-signal model: Finite r ds current source Slope = I/ V Ideal: zero slope r o = r o = " V " I SLOPE = " I " V = 1 r o V DS = V GS - V TH r o
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6 Caution: R on vs. r o confusion! R on Triode region Large signal True resistance (V-I through origin) r o Saturation region Small signal Models nonideality of current source V DS = V GS - V TH SATURATION TRIODE SLOPE = 1/r o SLOPE = 1/R on
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7 I D - V DS Characteristic for Different V GS "Family" of curves INCREASING V GS
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8 I D - V DS Characteristic for Different V GS Extrapolate backward: intersect at V DS -axis
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9 1/slope provides small signal resistance r o Intersect at -1/ λ Slope: Typical λ values: 0.01 V -1 L > 1μm 0.2 V -1 L < 1 μm 1 r o = I D 1 " # r o = 1 I D
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10 MOSFET small signal model r o in parallel: Model nonideality of current source due to channel length modulation r o = 1 " I D g m = 2 I D V GS " V TH r o
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This note was uploaded on 10/13/2009 for the course ECE 4902 taught by Professor Mcneill during the Spring '01 term at WPI.

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4902_C2009_Studio_5_short.ppt - Studio 5 Review Current...

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