Envelope-Controlled Cascode Doherty Amplifier Bias for Low Load Current
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Solution Overview
Problem
Doherty amplifiers face efficiency and linearity tradeoffs due to inherent AMAM/AMPM discontinuity, and envelope tracking techniques require high load currents and capacitances, which can compromise performance.
Innovation Solution
A Doherty amplifier system with a cascode configuration and an envelope tracking bias circuit providing a bias signal to the peaking amplifier's output transistor, reducing load current and capacitance, and using a scaling/shifting/delay circuit to optimize bias signals for improved efficiency and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If envelope tracking technique is implemented to improve efficiency, then power efficiency is improved, but load current and capacitance requirements increase
Solution Approach 1:
The amplifier is divided into two separate amplifiers (first and second amplifiers) with different biasing arrangements. The first amplifier operates with a first bias signal while the second amplifier operates with a second bias signal, allowing each to be optimized for different operating conditions. This segmentation enables efficient operation across varying power levels without requiring high load currents and capacitances throughout the entire system.
Solution Approach 2:
The bias signals provided to the amplifiers are made dynamic rather than fixed. The first bias signal and second bias signal can be adjusted independently based on operating conditions, enabling the system to adapt its efficiency characteristics dynamically. This dynamic biasing allows the amplifiers to maintain optimal efficiency across different power output levels while avoiding the need for continuously high load current and capacitance.
2Power
If Doherty amplifier configuration is used to improve power output, then power capability is improved, but AMAM/AMPM discontinuity causes linearity degradation
Solution Approach 1:
Each amplifier is given a different local biasing characteristic tailored to its specific function. The first amplifier receives a first bias signal optimized for its operating range, while the second amplifier receives a second bias signal optimized for its operating range. This local optimization of biasing conditions allows each amplifier to maintain linearity in its respective operating domain while collectively providing high power output capability.
Solution Approach 2:
The biasing parameters of the amplifiers are changed and optimized independently. By providing different bias signals to the first and second amplifiers, the system can adjust the operating parameters of each amplifier to minimize AMAM/AMPM discontinuity effects. This parameter optimization enables the maintenance of linearity even as power output capability is enhanced through the Doherty configuration.
Data Source
AI summary
In some embodiments, an amplifier system can include an amplifier circuit having first and second amplifiers configured to amplify respective first and second portions of an input signal. Each of the first and second amplifiers can include a cascode stage with input and output transistors arranged in a cascode configuration. The amplifier system can further include an envelope tracking bias circuit coupled to the amplifier circuit and configured to provide a bias signal to the output transistor of the cascode stage of at least one of the first and second amplifiers. The amplifier system can further include a supply circuit configured to provide a non-envelope tracking supply voltage to the output transistor of the cascode stage of the at least one of the first and second amplifiers.