Cascaded Class-AB Doherty Amplifier for Lower Distortion
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Solution Overview
Problem
Doherty amplifiers face challenges with high distortion due to Class-C peaking amplifiers, leading to AM-AM and AM-PM distortions, and have inefficiencies and bulkiness, making them unsuitable for applications like active antenna systems and mobile devices.
Innovation Solution
A Doherty amplifier configuration using multiple Class-AB amplifiers in cascade configurations for both main and peaking stages, with specific biasing to emulate Class-C behavior, reducing distortion and improving power added efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If Class-C peaking amplifiers are used in Doherty configuration, then power added efficiency is improved, but distortion increases due to AM-AM and AM-PM effects
Solution Approach 1:
The patent changes the operating class parameter from Class-C to Class-AB for the peaking amplifier, fundamentally altering its operational characteristics. This parameter change allows the amplifier to maintain higher efficiency while reducing the severe nonlinearity and distortion associated with Class-C operation, particularly the AM-AM and AM-PM distortions that plague traditional Doherty amplifiers.
2Loss of energy
If traditional Doherty amplifier configuration is used, then efficiency is improved, but device complexity and bulkiness increase making it unsuitable for mobile applications
Solution Approach 1:
The patent merges the main amplifier and peaking amplifier into a single integrated structure where both amplifiers share common components such as the output matching network and biasing circuitry. This consolidation reduces the overall device complexity and footprint while maintaining the efficiency benefits of the Doherty configuration, making it suitable for space-constrained mobile applications.
Solution Approach 2:
The patent designs the amplifier stages to perform multiple functions: the Class-AB peaking amplifier not only provides peak power amplification but also contributes to back-off power amplification when properly biased. This multi-functionality reduces the need for separate dedicated components, thereby simplifying the overall device structure and reducing bulkiness.
3Reliability
If multistage Class-AB amplifiers are used, then linearity is maintained, but power handling capability and efficiency are limited
Solution Approach 1:
The patent employs dynamic biasing techniques where the biasing conditions of the Class-AB amplifiers are adjusted based on the input signal level. During peak power operation, the biasing is optimized for maximum power handling, while during back-off operation, the biasing is adjusted to maintain optimal linearity. This dynamic adaptation allows the amplifier to achieve both high power handling capability and good linearity across different operating conditions.
Data Source
AI summary
A multistage linear power amplifier receiving an input signal. The multistage linear power amplifier comprises a plurality of Class-AB amplifiers connected in a cascade configuration. The plurality of Class-AB amplifiers amplifies the input signal to generate an amplified input signal. At least one of the plurality of Class-AB amplifiers is biased such that the multistage linear power amplifier emulates a Class-C amplifier.