Doherty Amplifier Envelope Biasing for Efficiency and Linearity
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Solution Overview
Problem
Doherty amplifiers face efficiency and linearity tradeoffs due to inherent AMAM/AMPM discontinuity and require envelope tracking systems with high load currents and capacitances, which can be inefficient and complex.
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 optimizing efficiency and linearity through envelope control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If envelope tracking is implemented with high load currents and capacitances to achieve high efficiency, then power added efficiency is improved, but system complexity and current requirements increase
Solution Approach 1:
The amplifier is divided into two separate amplifiers (first amplifier and second amplifier) with different biasing schemes. 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 specific operating conditions. This segmentation enables efficient operation across different power levels without requiring a complex single-stage envelope tracking system.
Solution Approach 2:
Different bias signals are applied to different amplifiers based on their specific operating requirements. The first amplifier receives a bias signal optimized for its operating range, while the second amplifier receives a different bias signal optimized for its operating range. This local optimization allows each amplifier to operate at peak efficiency in its designated range, reducing the need for high overall load currents and capacitances.
2Use of energy by moving object
If Doherty amplifier configuration is used to improve efficiency at power back-off, then power added efficiency is improved, but AMAM/AMPM discontinuity degrades linearity
Solution Approach 1:
The bias signals applied to the amplifiers are made dynamic rather than static. The first bias signal and second bias signal are adjusted based on operating conditions to maintain optimal performance across different power levels. This dynamic biasing compensates for the inherent AMAM/AMPM discontinuity in Doherty configurations, improving linearity while preserving efficiency benefits.
Solution Approach 2:
The bias parameters of the amplifiers are changed and optimized for different operating conditions. By adjusting the bias signals dynamically, the system can maintain consistent performance characteristics across the full power range, reducing the discontinuity effects that normally degrade linearity in Doherty amplifiers.
3Device complexity
If single amplifier configuration is used to simplify system design, then device complexity is reduced, but efficiency at power back-off deteriorates
Solution Approach 1:
The system is segmented into two amplifiers with different biasing schemes rather than using a single amplifier. This segmentation allows the system to maintain high efficiency at power back-off by having one amplifier operate in saturation while the other operates in linear region, combining their outputs to achieve both simplicity and high efficiency.
Solution Approach 2:
The two-amplifier configuration serves multiple functions: it provides high efficiency at power back-off, maintains good linearity through dynamic biasing, and keeps the overall system relatively simple by using standard amplifier building blocks. Each amplifier can be designed using conventional approaches, but their combined operation achieves superior performance.
Data Source
AI summary
Doherty amplifier having envelope control. In some embodiments, an amplifier system can include a Doherty amplifier having a carrier amplifier and a peaking amplifier, with each of the carrier amplifier and the peaking amplifier including 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 Doherty amplifier and configured to provide a bias signal to the output transistor of the cascode stage of the peaking amplifier.