Multistage Power Amplifier Biasing for PAE and Linearity

Solution Overview

Problem

Conventional power amplifiers, especially those used in space vehicles, face challenges in being both power efficient and small, while maintaining good amplitude modulation to amplitude modulation (AM-AM) and amplitude modulation to phase modulation (AM-PM) transfer characteristics, and often suffer from significant distortion and limited input ranges and bandwidths.

Innovation Solution

A multistage power amplifier design where each stage operates at or near its power added efficiency (PAE) peak, with drive circuits biasing the amplifiers to achieve optimal power transfer characteristics, and the output impedance of each stage is matched to ensure efficient power delivery across the amplifier chain.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If conduction angle biasing is used to improve power efficiency, then power efficiency is improved, but AM-AM and AM-PM transfer characteristics deteriorate with significant distortion

Engineering Contradiction:

Improvepower efficiencyVSAvoidAM-AM and AM-PM transfer characteristics

Core Design Contradiction:

Loss of energyVSManufacturing precision

Solution Approach 1:

The amplifier is divided into multiple stages, each operating at different conduction angles optimized for their specific function. The first stage operates at a higher conduction angle for linearity, while subsequent stages operate at lower conduction angles for efficiency, with each stage contributing to the overall power efficiency improvement without sacrificing overall transfer characteristics

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the operating parameters of different amplifier stages by biasing each stage to operate at or near its PAE peak at different conduction angles. This parameter optimization allows each stage to contribute to power efficiency while the cumulative effect maintains acceptable AM-AM and PM-PM characteristics

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If conventional power efficient amplifiers (Doherty, Chireix, EER) are used, then power efficiency is improved, but device complexity and size increase

Engineering Contradiction:

Improvepower efficiencyVSAvoidamplifier complexity and size

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The amplifier is divided into multiple stages, each operating at different conduction angles optimized for their specific function. The first stage operates at a higher conduction angle for linearity, while subsequent stages operate at lower conduction angles for efficiency, with each stage contributing to the overall power efficiency improvement without sacrificing overall transfer characteristics

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the operating parameters of different amplifier stages by biasing each stage to operate at or near its PAE peak at different conduction angles. This parameter optimization allows each stage to contribute to power efficiency while the cumulative effect maintains acceptable AM-AM and PM-PM characteristics

Inventive Principle:

Principle #35Parameter changes

3Volume of moving object

If single stage amplifiers are used, then device size is reduced, but power efficiency and power transfer characteristics deteriorate

Engineering Contradiction:

Improveamplifier sizeVSAvoidpower efficiency

Core Design Contradiction:

Volume of moving objectVSLoss of energy

Solution Approach 1:

The amplifier is divided into multiple stages, each operating at different conduction angles optimized for their specific function. The first stage operates at a higher conduction angle for linearity, while subsequent stages operate at lower conduction angles for efficiency, with each stage contributing to the overall power efficiency improvement without sacrificing overall transfer characteristics

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the operating parameters of different amplifier stages by biasing each stage to operate at or near its PAE peak at different conduction angles. This parameter optimization allows each stage to contribute to power efficiency while the cumulative effect maintains acceptable AM-AM and PM-PM characteristics

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS7948324B2Power efficient multistage amplifier and design method

Publication Date: 2011.05.24 VIASAT INC

AI summary

A multistage amplifier and design method are disclosed. The multistage amplifier has a plurality of amplifier stages, each stage having an amplifier designed and biased to operate at or near the amplifier's power added efficiency (PAE) peak. The PAE peak of each of the amplifier is at or near the amplifiers linear-compression transition region, providing a multistage power amplifier that is power efficient and has desirable amplitude to amplitude and amplitude to phase power transfer characteristics. The amplifier is designed by matching the output impedance of a final stage with a load. Amplifier stages are iteratively designed from the last stage to the first. At each stage, an amplifier and drive circuit are designed. The drive circuit and amplifier are designed to provide each stage with output impedance matched to the input impedance of the following stage and to operate at or near the PAE peak of the amplifier.