ch10 - Chapter 10 Differential Amplifiers 10.1 General...

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1 Chapter 10 Differential Amplifiers 10.1 General Considerations 10.2 Bipolar Differential Pair 10.3 MOS Differential Pair 10.4 Cascode Differential Amplifiers 10.5 Common-Mode Rejection 10.6 Differential Pair with Active Load
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CH 10 Differential Amplifiers 2 Audio Amplifier Example An audio amplifier is constructed above that takes on a rectified AC voltage as its supply and amplifies an audio signal from a microphone.
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CH 10 Differential Amplifiers 3 “Humming” Noise in Audio Amplifier Example However, V CC contains a ripple from rectification that leaks to the output and is perceived as a “humming” noise by the user.
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CH 10 Differential Amplifiers 4 Supply Ripple Rejection Since both node X and Y contain the ripple, their difference will be free of ripple. in v Y X r Y r in v X v A v v v v v v A v = - = + =
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CH 10 Differential Amplifiers 5 Ripple-Free Differential Output Since the signal is taken as a difference between two nodes, an amplifier that senses differential signals is needed.
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CH 10 Differential Amplifiers 6 Common Inputs to Differential Amplifier Signals cannot be applied in phase to the inputs of a differential amplifier, since the outputs will also be in phase, producing zero differential output. 0 = - + = + = Y X r in v Y r in v X v v v v A v v v A v
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CH 10 Differential Amplifiers 7 Differential Inputs to Differential Amplifier When the inputs are applied differentially, the outputs are 180° out of phase; enhancing each other when sensed differentially. in v Y X r in v Y r in v X v A v v v v A v v v A v 2 = - + - = + =
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CH 10 Differential Amplifiers 8 Differential Signals A pair of differential signals can be generated, among other ways, by a transformer. Differential signals have the property that they share the same average value to ground and are equal in magnitude but opposite in phase.
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CH 10 Differential Amplifiers 9 Single-ended vs. Differential Signals
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CH 10 Differential Amplifiers 10 Differential Pair With the addition of a tail current, the circuits above operate as an elegant, yet robust differential pair.
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CH 10 Differential Amplifiers 11 Common-Mode Response 2 2 2 1 2 1 EE C CC Y X EE C C BE BE I R V V V I I I V V - = = = = =
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CH 10 Differential Amplifiers 12 Common-Mode Rejection Due to the fixed tail current source, the input common- mode value can vary without changing the output common- mode value.
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CH 10 Differential Amplifiers 13 Differential Response I CC Y EE C CC X C EE C V V I R V V I I I = - = = = 0 2 1
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CH 10 Differential Amplifiers 14 Differential Response II CC X EE C CC Y C EE C V V I R V V I I I = - = = = 0 1 2
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CH 10 Differential Amplifiers 15 Differential Pair Characteristics None-zero differential input produces variations in output currents and voltages, whereas common-mode input produces no variations.
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16 Small-Signal Analysis Since the input to Q 1 and Q 2 rises and falls by the same amount, and their bases are tied together, the rise in I C1 has the same magnitude as the fall in I C2 . I
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ch10 - Chapter 10 Differential Amplifiers 10.1 General...

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