The document discusses different modes of operation and transfer characteristics of differential amplifiers. It covers various circuit implementations of differential pairs using BJTs and MOSFETs, including current mirrors, active loads, and multistage amplifiers. Analysis techniques are presented for determining signal currents and evaluating differential gain, input resistance, and frequency response.

1. EE-4232
Differential Amplifiers
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2. Different modes of operation of the differential pair: The differential pair with a common-
mode input signal vCM.
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3. Different modes of operation of the differential pair: The differential pair with a “large”
differential input signal.
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4. Different modes of operation of the differential pair: The differential pair with a large input
signal of polarity opposite to that in (b).
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5. Different modes of operation of the differential pair: The differential pair with a small
differential input signal vi.
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6. Transfer characteristics of the BJT differential pair of previous figure assuming α ≅ 1.
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7. The current and voltages in the differential amplifier when a small
difference signal vd is applied.
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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.
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9. A differential amplifier with emitter existence. Only signal quantities are shown (on color).
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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.
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11. (a) The differential amplifier fed by a common-mode voltage signal. (b) Equivalent
“half-circuits” for the common-mode calculations.
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12. Analysis of the current mirror taking into account the finite β of the BJTs.
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13. Generation of a number of cross currents.
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14. A current mirror with base-current compensation.
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15. The Wilson current mirror.
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16. The Widlar current source.
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18. A differential amplifier with an active load.
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19. Small-signal model of the differential amplifier.
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20. The MOSFET differential pair.
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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).
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22. MOS current mirrors: basic
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23. MOS current mirrors: cascode
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24. MOS current mirrors: Wilson
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25. MOS current mirrors: modified Wilson
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26. A multistage amplifier circuit.
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27. References
• Electronics by A. Hambley
• Microelectronics Circuits by Sedra & Smith
• Other books on Electronics
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