1. Differential Amplifiers: Second Stage Dr. Paul Hasler

2. Differential Transistor Pairs MOSFET Diff-PairBJT Diff-Pair The bottom transistor (the one with I bias ) sets the total current The upper two transistors compete for a fraction of this current

3. BJT Differential Pair Analysis

4. Analysis of Diff-Pair Source of Common-Mode Gain

5. Differential Pair Currents -0.4 3 2 100.10.20.30.4 0 0.5 1 1.5 2 2.5 3 Differential input voltage (V) Output current (nA) I out + I out -

6. Above V T MOSFET Large-Signal

7. I SS  i D1  i D2 Start with 2 equations

8. Above V T MOSFET Large-Signal I SS  i D1  i D2 Start with 2 equations

9. Above V T MOSFET Large-Signal I SS  i D1  i D2 Start with 2 equations

10. Above V T MOSFET Large-Signal I SS  i D1  i D2 Start with 2 equations

11. Above V T MOSFET Large-Signal I SS  i D1  i D2 Start with 2 equations

13. Gain Changes with Bias Current

14. Common-Mode Input Range Maximum: Q1 in Forward-activeMinimum: Q3 in Forward-active

15. MOS Common-Mode Input Range Maximum: M1 in Saturation Minimum: M3 in Saturation v ic (max) = V DD - 0.5I SS R D -v DS1 (sat)+V GS1 = V DD - 0.5I SS R D + V T1 v ic (min) = V SS +v DS3 (sat)+V GS1

16. Micro-Surgery

17. Small Signal: BJT Diff-Pair

18. Common-Mode Circuit

19. An emitter-degenerated amplifier Gain ~ - R c / (2 R EE )

20. MOS Common-Mode Circuit

21. An emitter-degenerated amplifier Gain ~ - R D / (2 R ss )

22. Differential-Mode Gain

23. Gain = - g m R c CMRR ~ - 2 g m R E ~ - 2 (I EE / 2 U T ) R E

24. MOS Differential Mode Circuit

25. Gain = - g m R D CMRR ~ - g m R ss ~ - (I ss / ( V gs - V T ) ) R ss

26. Mismatch in Transistor Circuits Outline The general approach to analyzing mismatches Input voltage and current offsets of BJT differential amplifiers Input voltage offsets of MOS differential amplifiers Objective The objective of this presentation is: 1.) Illustrate the method of analyzing mismatches 2.) Analyze the input current and voltage offsets for differential amplifiers

27. BJT Mismatch Modeling

28. Mismatch Modeling in MOS

29. BJT Mismatch Modeling

30. Differential Amplifiers II Review of Basic Differential Pairs Above Threshold Differential Amplifiers Small-Signal Analysis: Differential and Common mode circuits Modeling of Mismatch