Doherty Peaking Amplifier Bias Modulation for Wideband Linearity
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Solution Overview
Problem
Doherty-type power amplifiers in radio frequency transmitters face challenges in achieving improved energy efficiency and linearity during power amplification, particularly in meeting the higher data rate requirements of modern mobile communication devices like 5G-NR.
Innovation Solution
A power amplifier system is introduced, featuring a carrier amplifier, a peaking amplifier, and an envelope tracking power supply that generates modulated voltage signals to control the bias of both amplifiers, allowing the peaking amplifier to operate in Class C and quickly bias/debias based on the modulated power supply voltage, thereby enhancing efficiency and reducing memory effects without detecting wide modulation envelopes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a Doherty amplifier uses carrier and peaking amplifiers to operate between average power and peak power, then power amplification capability is improved, but energy efficiency and linearity deteriorate
Solution Approach 1:
The patent applies dynamics by making the bias voltage of the peaking amplifier dynamically adjustable based on the envelope voltage. The bias controller continuously adapts the bias point according to the instantaneous envelope level, allowing the peaking amplifier to operate in different classes (AB at low power, C at high power) throughout the modulation cycle, thereby optimizing energy efficiency across the entire power range while maintaining power amplification capability
Solution Approach 2:
The patent changes the bias voltage parameter of the peaking amplifier based on the envelope voltage level. By varying the bias voltage dynamically - using a first bias voltage when envelope voltage is below a threshold and a second bias voltage when above - the system optimizes the operating point to improve energy efficiency while maintaining the required power amplification performance
2Use of energy by moving object
If the peaking amplifier operates in Class C for high efficiency, then energy efficiency is improved, but linearity and memory effects deteriorate
Solution Approach 1:
The system dynamically adjusts the bias point of the peaking amplifier based on the envelope voltage level. During low-power portions of the modulation envelope, the bias is set to Class AB for linear operation, while during high-power portions, it transitions to Class C for efficiency. This dynamic adaptation resolves the contradiction by providing the appropriate operating class at the appropriate time, maintaining both linearity and efficiency
Solution Approach 2:
The bias controller anticipates the need for linearity by maintaining a higher bias voltage (Class AB operation) during low-envelope-voltage conditions before non-linear distortion becomes problematic. This preliminary maintenance of linear operating conditions prevents memory effects and distortion from occurring in the first place, while still allowing efficient Class C operation during high-power segments
Data Source
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AI summary
A power amplifier system is disclosed with a carrier amplifier having a carrier bias input and a carrier supply node and a peaking amplifier having a peaking bias input and a peaking supply node. Also included is an envelope tracking power supply having a modulated voltage supply output coupled to the peaking supply node. Further included is a peaking bias controller having a peaking bias control input coupled to the peaking supply node and a peaking bias control output coupled to the peaking bias input, wherein the peaking bias controller is configured to generate in response to a modulated peaking supply voltage generated by the envelope tracking power supply at the peaking supply node a modulated peaking bias signal that controls bias of the peaking amplifier.