最新精品-最新精品范文-chapter_5 Differential and multistage amp(For IT class).ppt

Chapter 5  Differential and Multistage Amplifier
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Outline
Introduction
The CMOS Differential Pair
Small-Signal Operation of the MOS Differential Pair
The BJT Differential Pair
The differential Amplifier with Active Load
Frequency Response of the Differential amplifier
Multistage Amplifiers
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Introduction
Two reasons of the differential amplifier suited for IC fabrication:
IC fabrication is capable of providing matched devices.
Utilizing ponents than single-ended amplifier:
Differential circuits are much less sensitive to noise and interference.
Differential configuration enable us to bias the amplifier and to couple amplifier stages without the need for bypass and coupling capacitors.
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The MOS Differential Pair
Basic structure of differential pair.
Characteristics
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The MOS Differential Pair
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Operation with mon –Mode Input Voltage
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Operation with mon –Mode Input Voltage
Symmetry circuit.
Common-mode voltage.
Current I divides equally between two transistors.
The difference between two drains is zero.
The differential pair rejects mon-mode input signals.
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Operation with a Differential Input Voltage
The MOS differential pair with a differential input signal vid applied.
With vid positive: vGS1 > vGS2, iD1 > iD2, and vD1 < vD2; thus (vD2 - vD1) will be positive.
With vid negative: vGS1 < vGS2, iD1 < iD2, and vD1 > vD2; thus (vD2 - vD1) will be negative.
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Operation with a Differential Input Voltage
Differential input voltage.
Response to the differential input signal.
The current I can be steered from one transistor to the other by varying the differential input voltage in the range:
When differential input voltage is very small, the differential output voltage is proportional to it, and the gain is high.
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Large-Signal Operation
Transfer characteristic curv