Doherty Peaking Amplifier Bias Modulation for Efficiency and Linearity
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Solution Overview
Problem
Existing Doherty amplifiers in radio frequency transmitters face challenges in achieving improved energy efficiency and linearity during power amplification, particularly in mobile communication devices requiring higher data rates.
Innovation Solution
A power amplifier system with a carrier and peaking amplifier, controlled by an envelope tracking power supply and bias controllers, modulates the bias signals based on the modulated power supply voltage to optimize operation and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the peaking amplifier operates in Class C at low power levels, then energy efficiency is improved, but linearity deteriorates
Solution Approach 1:
The patent implements dynamic class switching for the peaking amplifier, transitioning between Class C operation at low power levels and Class AB operation at high power levels. This is achieved through an envelope tracker that dynamically adjusts the bias voltage based on the RF signal envelope, allowing the amplifier to adapt its operating class to the instantaneous power level, thereby optimizing both efficiency and linearity across different operating conditions
Solution Approach 2:
The patent changes the bias voltage parameter dynamically using an envelope tracker. The bias voltage is modulated in accordance with the envelope of the RF signal, enabling the peaking amplifier to switch between different operating classes. This parameter change allows the amplifier to maintain optimal efficiency at low power (Class C) while ensuring sufficient linearity at high power levels (Class AB)
2Productivity
If the peaking amplifier quickly switches classes, then productivity is improved, but device complexity increases
Solution Approach 1:
The patent introduces an envelope tracker as an intermediary device between the RF signal source and the peaking amplifier. The envelope tracker extracts the envelope information from the RF signal and uses it to control the bias voltage of the peaking amplifier, enabling fast class switching without requiring complex direct control circuits. This intermediary approach simplifies the overall control architecture while achieving high-speed operation
Solution Approach 2:
The envelope tracker implements a feedback mechanism by continuously monitoring the RF signal envelope and adjusting the bias voltage accordingly. This feedback loop enables the peaking amplifier to respond rapidly to changes in signal power level, achieving fast class switching. The feedback approach provides automatic adaptation without requiring complex open-loop control circuits
Data Source
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.