Quadrature Doherty Amplifier Biasing for Efficient Envelope Control
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Solution Overview
Problem
Doherty amplifiers face efficiency and linearity tradeoffs due to inherent AMAM/AMPM discontinuities 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 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 is implemented with high load current and capacitance to achieve high efficiency, then power added efficiency is improved, but device complexity and loss of substance increase
Solution Approach 1:
The patent extracts only the essential envelope tracking function by providing bias signals to specific transistors (output transistor of peaking amplifier and cascode transistor of carrier amplifier) rather than implementing full envelope tracking across all amplifier stages. This selective approach maintains power added efficiency while reducing system complexity and envelope control current requirements
Solution Approach 2:
The patent applies envelope tracking locally to specific critical components (peaking amplifier output transistor and carrier amplifier cascode transistor) rather than uniformly across the entire amplifier system. This localized application optimizes efficiency at key points while minimizing overall complexity and resource consumption
2Stability of the object's composition
If envelope tracking bias circuit provides bias signal to multiple transistors to maintain linearity, then amplification linearity is improved, but load current and capacitance requirements increase
Solution Approach 1:
The patent extracts the essential linearity-maintaining function by providing envelope tracking bias signals to only two critical transistors (the peaking amplifier output transistor and the carrier amplifier cascode transistor) rather than all transistors in the Doherty amplifier. This selective biasing maintains sufficient amplification linearity while dramatically reducing envelope control current requirements compared to comprehensive biasing approaches
3Device complexity
If Doherty amplifier uses traditional configuration without selective envelope tracking, then device complexity is reduced, but power added efficiency and amplification linearity deteriorate
Solution Approach 1:
The patent applies envelope tracking selectively to specific critical components (peaking amplifier output transistor and carrier amplifier cascode transistor) rather than implementing it uniformly across all amplifier stages. This localized application improves power added efficiency and linearity at key points while maintaining relatively simple overall system architecture, avoiding the complexity of full-system envelope tracking
Data Source
AI summary
Quadrature amplifier having envelope control. In some embodiments, an amplifier system can include a quadrature amplifier having first and second amplifiers configured to amplify first and second signals in quadrature relative to each other, with each of the first and second amplifiers 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 quadrature amplifier 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.