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# Diff Amps

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ALL ABOUT HOW IT WORKS AND ITS ANALYSIS

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### Diff Amps

1. 1. EE-4232 Differential Amplifiers 0
2. 2. Different modes of operation of the differential pair: The differential pair with a common- mode input signal vCM. 1
3. 3. Different modes of operation of the differential pair: The differential pair with a “large” differential input signal. 2
4. 4. Different modes of operation of the differential pair: The differential pair with a large input signal of polarity opposite to that in (b). 3
5. 5. Different modes of operation of the differential pair: The differential pair with a small differential input signal vi. 4
6. 6. Transfer characteristics of the BJT differential pair of previous figure assuming α ≅ 1. 5
7. 7. The current and voltages in the differential amplifier when a small difference signal vd is applied. 6
8. 8. A simple technique for determining the signal currents in a differential amplifier excited by a differential voltage signal vd; dc quantities are not shown. 7
9. 9. A differential amplifier with emitter existence. Only signal quantities are shown (on color). 8
10. 10. Equivalence of the differential amplifier (a) to the two common-emitter amplifiers in (b). This equivalence applies only for differential input signals. Either of the two common-emitter amplifiers in (b) can be used to evaluate the differential gain, input differential resistance, frequency response, and so on, of the differential amplifier. 9
11. 11. (a) The differential amplifier fed by a common-mode voltage signal. (b) Equivalent “half-circuits” for the common-mode calculations. 10
12. 12. Analysis of the current mirror taking into account the finite β of the BJTs. 11
13. 13. Generation of a number of cross currents. 12
14. 14. A current mirror with base-current compensation. 13
15. 15. The Wilson current mirror. 14
16. 16. The Widlar current source. 15
17. 17. 16
18. 18. A differential amplifier with an active load. 17
19. 19. Small-signal model of the differential amplifier. 18
20. 20. The MOSFET differential pair. 19
21. 21. Normalized plots of the currents in a MOSFET differential pair. Note that VGS is the gate-to-source voltage when the drain current is equal to the dc bias current (I/2). 20
22. 22. MOS current mirrors: basic 21
23. 23. MOS current mirrors: cascode 22
24. 24. MOS current mirrors: Wilson 23
25. 25. MOS current mirrors: modified Wilson 24
26. 26. A multistage amplifier circuit. 25
27. 27. References • Electronics by A. Hambley • Microelectronics Circuits by Sedra & Smith • Other books on Electronics 26