# 单极放大器概述

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# Applications and General Considerations

Applications of Amplifier:

2. to overcome the noise of a subsequent stage
3. to provide logical levels to a digital circuit
4. to play a role in feedback systems (Chapter 8)

Amplifier categories

Common-Source Stage (共源) Source Follower (源极跟随器) Common-Gate Stage (共栅) Cascode (共源共珊)
With Source Degeneration

For each amplifier above, we will

1. analyze the MOS’s stage using the equation we learn at chapter 1
2. introduce the small-signal model
3. discuss how to increase the gain

An ideal amplifier: output is a linear replica of the input: $y(t)=\alpha_1 x(t)$, where $\alpha_1$ denote the gain. if we consider the bias (dc operating) point, the overall output is $y(t)=\alpha_0+\alpha_1 x(t)$

Any amplifier is a compomise (trade-off) between “analog design octagon”: In this chapter, we are going to discuss how to calculate $A_v$ and $r_o$