1. Lecture 6 Active Load Amplifier Multistage Amplifier Circuit

2. Differential to Single-Ended Conversion Reason for converting the signal from differential to single ended—to drive an offchip load.

3. A Simple Circuit for Differential to Single-Ended Conversion Problem: the drain signal current of Q1 is wasted!

4. If Q 4 is perfectly matched to Q 3 I(Q3)=I(Q4)=I/2 V o =V DD -V SG3

5. If Q 4 is NOT perfectly matched to Q 3

6. Small Signal Operation See next slide

7. Virtual Ground Common Drain Gain: (Drain Resistance)/(1/gm+Source Resistance) Low Res into the drain of Q3 High Res into the drain of Q4 Not a virtual ground (Strictly Speaking)

8. Analysis Technique Short circuit transconductance Output resistance

9. Short Circuit Transcondutance Virtual Ground Justification: 1.The drain of Q4 is grounded! 2.The resistance into Q3 is low! (e.g. 1/g m3 ) 3.Therefore, we have an approximate virtual ground. Approximations: 1.r o1 >>1/g m3 2.r o3 >>1/g m3 Implications of the short at the output: 1.r o4 is shorted out. 2.r o2 is shorted out.

10. Output Resistance

11. A 2-Stage CMOS Op-Amp

12. A Bias Circuit that Stabilizes g m

13. Materials Not Covered in Class

14. CMRR Circuit