EECE 311 Lecture, Spring 2012

1 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 • Function of v, • Function of vo – v = VDD – vo – Q2 sat: vo < VDD-|VOV2| EECE 311 - Introduction 2  I-V (Q2) v i (1) v=0 (2) v=|Vov2| vo i (1) vo=VDD (2) vo=VDD-|Vov2| Q2 saturation Q2 saturation • I-V of Q1 – Function of vo, EECE 311 - Introduction 3  I-V (Q1) vo i Q1 saturation Increasing vi • Intersection of – I-V(Q1) – I-V(Q2) provides the solution space EECE 311 - Introduction 4  Q1 & Q2 (i vs. vo) vo i (1) vo=VDD (2) vo=VDD-|Vov2| Q2 saturation vo i Q1 saturation EECE 311 - Introduction 5  Q1 & Q2 (i vs. vo) vo (1) vo=VDD (2) vo=VDD-|Vov2| Q2 saturation i Q1 saturation (3) vo=Vov1 VOA VOB Q2 sat: vo < VDD-|VOV2| Q1 sat: vo >|VOV1| EECE 311 - Introduction 6  Q1 & Q2 (i vs. vo) vo (1) vo=VDD (2) vo=VDD-|Vov2| Q2 saturation i Q1 saturation (3) vo=Vov1 VOA VOB • 1 2 ' 2 2 1 1 1 1 1 2 2 1 1 1 1 1 2 1 1 2 2 1 2 100 A 100 A 200 (10) 0.316V 100 0.633 mA/V 0.5 0.316V 20 200K 100 10 100K 100 Output resistance: // 66.67K Voltage gain: D D REF W D n OV OV L OV D m OV An o D Ap o D o o o I I I I k V V V I g V V r I V r I R r r                                 1 1 2 2 2 ' 1 1 2 2 2 2 2 1 // 42.2 V/V Limits of output voltage swing: 100 A 65 (10) 0.6 1.155V 1.155 0.6 0.555V enters SAT when: 3 0.555 2.445 V enters SAT when: v m o o W REF p SG tp SG L SG OV O DD OV O A g r r I k V V V V V Q v V V Q v                     1 0.316 V VOV  7  Solution: We will neglect channel- length modulation in DC analyses. (i.e., when we solve for ID, VOV) When we solve for small signal parameters we will consider those effects