Analog CMOS Integrated Circuit Design Differential...

Analog CMOS Integrated Circuit Design

Differential Amplifiers

Jawdat Abu-Taha Department of Electrical and Computer Engineering

Islamic University of Gaza

[email protected]

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Overview

• The “differential amplifier” is one of the most important circuit inventions.

• Their invention dates back to vacuum tube era (1930s.)

• Alan Dower Blumlein (a British Electronics Engineer, 1903- 1942) is regarded as the inventor

differential pair. of the vacuum-tube version of

• Differential operation offers many useful properties and is widely used in analog and mixed-signal integrated circuits

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Single-ended and Differential Signals

•A “single-ended” signal is a signal that is measured with respect to a fixed potential (typically ground.)

“ •Differential signal” is generally referred to a signal that

is measured as a difference between two nodes that have equal but opposite-phase signal excursions around a

fixed potential (the fixed potential is called common-mode

(CM) level.)

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Why Differential?

• Better immunity to environmental noise

• Improved linearity

• Higher signal swing compared to single-ended

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Higher Immunity to Noise Coupling

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Supply Noise Reduction

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Basic Differential Pair

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Basic Differential Pair

• Problem: Sensitive to input common-mode (CM) level

– Bias current of the transistors input CM level changes

M1 and M2 changes as the

– gm of the devices as well as output CM level change

• Can we think of a solution?

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Differential Pair

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Common-Mode Response

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Common-Mode Input versus Output Swing

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Example

• Using the half-circuit concept, calculate the small-signal

differential λ≠ 0.)

gain of the following circuit (for two cases of λ=0 and

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Example

• Using the half-circuit concept, calculate the small-signal

differential λ≠ 0.)

gain of the following circuit (for two cases of λ=0 and

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Example

• Sketch the small-signal gain of a differential pair as a function of

its input common-mode level.

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Analysis of Differential Amplifier

2 I D − V = V − V = + V , V VTH in1 in 2 GS1 GS 2 GS W

µnCox L

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Differential Gain

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Differential Pair as a CS and CD-CG Amplifier

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Example

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Differential Pair with MOS Loads

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MOS Loads

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MOS Loads

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Gilbert Cell

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Gilbert Cell

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Gilbert Cell

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Analog CMOS Integrated Circuit Design Differential...

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