Chapter 4-2

Introduction to Low Noise, High Power,

and Broadband Amplifier Design

Chien-Jung Li

Department of Electronics Engineering

National Taipei University of Technology

Department of Electronic Engineering, NTUT

Functional Block Diagram of Communication Systems

Input

Transducer

Output

Transducer

Input Signal

(Audio, Video, Data)

Output Signal

(Audio, Video, Data)

Transmitter

(Tx)

Receiver

(Rx)

Channel

• The main job of the communication systems is to transfer

useful information from one end to the other ends.

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Block Diagram of a Basic Radio System

• Transmitter (Tx)

• Receiver (Rx)

Data in

Modulator IF Filter Mixer

Bandpass Filter

(BPF) Power Amplifier

(PA)

Antenna

Local

Oscillator

(LO)

Bandpass Filter

(BPF) Mixer IF Filter

Data out

DemodulatorIF Amplifier

Local

Oscillator

(LO)

Low Noise

Amplifier

(LNA)

Antenna

This architecture was first called superheterodyne and patented in 1917 by

Armstrong. The “transceiver” means the system that combines Tx and Rx.

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Constant NF Circles

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Noise Circle and Gain Circles (I)

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Noise Circle and Gain Circles (II)

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Noise Circle and Gain Circles (III)

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Broadband Design

• The most popular and well-established circuit techniques

employed in the design of broadband amplifiers that are

generalized in hybrid and monolithic technologies are:

Reactively matched circuit

Traveling wave distributed circuit

Feedback circuit

Lossy matched circuit

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Broadband Stability

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Broadband v.s. Narrowband Matching

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PA Matching Considerations

• In order to obtain maximum output power, typically the power

amplifier is not conjugately matched. In stead, the load is designed

such that the amplifier has the correct voltage and current to deliver

the required power.

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Matching to S22* vesus Matching to Γopt

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Class A, AB, C PAs

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Power Contour

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Power Combing

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Cascaded PA

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