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Microwave Amplifier Design

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Microwave Amplifier Diagram

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Gain Definitions

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Cont’d

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After a few manipulations, we have:

Source Mismatch Factor

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P

T

AVS

ins G

GPP

M

Load Mismatch Factor

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A

T

AVN

LL G

GPPM

Example#1

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Cont’d

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Cont’d

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Stability Consideration

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Cont’d

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Stability Circle in the Smith Chart

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Stable and Unstable Regions in ΓL Plane

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Stable and Unstable Regions in Γs Plane

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Conditions for Unconditional Stability

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Example#2

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For f=500 MHz, we have:

For f=1 GHz, we have:

Cont’d

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Γs Plane

Cont’d

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ΓL Plane

Stability Consideration

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A straightforward but somewhat lengthy manipulations result in the following necessary and sufficient conditions for unconditional stability:

Stern’s stability factor:

Example#3

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Cont’d

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Example#4

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Cont’d

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Cont’d

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Improving Stability

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Unilateral Transistor: S12=0

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In a unilateral case we have:

Cont’d

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Maximum Achievable Gain(Unilateral Case: S12=0)

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Bilateral Transistor(S12≠0)

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Solving above equations, Γs and ΓL are obtained:

It is proven maximum gain is obtained when simultaneous conjugate match exists.

Maximum Achievable Gain (Bilateral Case: S12≠0)

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It is proven that:

The maximum stable gain is defined as the value of GTmax when K=1. Namely,

Example

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BJT Bias Network

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BJT Bias Network

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GaAs FET Bias Network

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GaAs FET Bias Network

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GaAs FET Bias Network

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GaAs FET Bias Network

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