CMOS Common Source Amplifier Region III Voltage Transfer Characteristics
An analysis of a CMOS common source amplifier operating in Region III, the high gain region. Details on saturation regions for transistors Q1 and Q2, voltage transfer characteristics, and intersection of I-V curves. Includes solutions and small signal parameters. Neglects channel-length modulation in DC analyses.
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Presentation Transcript
CMOS Common Source Amplifier Based on input voltage vI, vo follows the voltage transfer characteristics curve Region III is the high gain region: Q1 and Q2 are in saturation VIA < vI <VIB VOB < vo <VOA 1
Q2 saturation I-V (Q2) i (2) v=|Vov2| (1) v=0 v Q2 saturation i Function of v, Function of vo v = VDD vo Q2 sat: vo < VDD-|VOV2| (1) vo=VDD (2) vo=VDD-|Vov2| vo 2 EECE 311 - Introduction
I-V (Q1) i Q1 saturation Increasing vi vo I-V of Q1 Function of vo, EECE 311 - Introduction3
Q1 & Q2 (i vs. vo) Q1 saturation i vo Q2 saturation i Intersection of I-V(Q1) I-V(Q2) provides the solution space (1) vo=VDD (2) vo=VDD-|Vov2| vo 4 EECE 311 - Introduction
Q1 & Q2 (i vs. vo) Q1 saturation i Q2 saturation (1) vo=VDD (3) vo=Vov1 (2) vo=VDD-|Vov2| VOA vo VOB Q1 sat: vo >|VOV1| Q2 sat: vo < VDD-|VOV2| 5 EECE 311 - Introduction
Q1 & Q2 (i vs. vo) Q1 saturation i Q2 saturation (1) vo=VDD (3) vo=Vov1 VOB (2) vo=VDD-|Vov2| VOA vo vOA= VDD-|VOV2|=VDD-(VSG-|vtp|) can be derived from IQ3=Iref by solving for VSG vOB can be solved by equating: iQ2 =iQ1 @ vo=vov1 iQ2= 1 iQ1= 1 2?? ? 2?? ? ?(??? |???|)2(1 +??? ???1 ?(???1)2(1 +???1 ) ?? ??) EECE 311 - Introduction6
= = = = 100 A I I I Solution: 1 2 D D REF = = 200 (10) ' 2 2 100 A = I k V V W L 1 2 1 2 1 1 1 D n OV OV 0.316V V 1 OV 100 I V = = = 0.633 mA/V 1 g D 1 m 0.5 0.316V 20 200K 100 1 2 1 OV V I = = = An r 1 o 1 D V 10 Ap = = = 100K r 2 o 100 I 2 D Output resistance: // Voltage gain: A g = We will neglect channel- length modulation in DC analyses. (i.e., when we solve for ID, VOV) = = 66.67K R r r 1 2 o o o ( ) = // 42.2 V/V r r 1 1 2 v m o o When we solve for small signal parameters we will consider those effects Limits of output voltage swing: ( ) 2 ( ) 2 = = = 65 (10) ' p 100 A 0.6 I k V V V W L 1 2 1 2 REF SG tp SG = = = 1.155V 1.155 0.6 0.555V V V 2 SG OV enters SAT when: V V = Q v Q v 2 3 0.555 = = 2.445 V 2 O DD OV enters SAT when: 0.316 V OV V = = 1 7 1 O
