N-Way Doherty Amplifier Bias Tracking for High Back-Off Efficiency
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Solution Overview
Problem
High power communication systems face inefficiencies in power amplifiers due to high peak-to-average power ratios (PAPR) in OFDM signals, particularly in N-way Doherty amplifiers, which suffer from reduced gain and efficiency at high output back-off powers and increased power dissipation.
Innovation Solution
The implementation of a dual-feed distributed amplifying method in N-way Doherty amplifiers using hybrid couplers and transmission lines, along with adaptive bias supply techniques such as envelope tracking and average power tracking, enhances gain and efficiency performance by optimizing the operation of main and peaking amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional N-way Doherty amplifier uses multiple parallel transistors of identical devices, then efficiency at high output back-off power is improved, but total gain is reduced due to loss of N-way input power splitter
Solution Approach 1:
The patent applies dynamics by making the bias voltages adaptive rather than fixed. The drain bias voltages and gate bias voltages are dynamically adjusted based on the input power level through power detection circuitry. This allows the amplifier to optimize its operating point continuously, resolving the contradiction between maintaining high efficiency at back-off power and preserving total gain by compensating for splitter losses through adaptive bias control.
2Loss of energy
If asymmetric Doherty amplifier uses different power device sizes for main and peaking amplifiers, then high efficiency at various back-off powers is obtained, but optimization of gain and output power becomes difficult due to different device matching circuits and delay mismatch
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the bias voltages (drain and gate) based on input power level. Instead of fixing the operating parameters for asymmetric devices, the system continuously modifies these parameters to compensate for the complexity introduced by different device sizes and matching circuits, thereby maintaining both efficiency and gain without requiring complex manual optimization.
Solution Approach 2:
The patent implements feedback through power detection circuitry that monitors the input power level and uses this information to adaptively control the bias voltages. This feedback mechanism allows the system to automatically compensate for the matching circuit differences and delay mismatches in asymmetric configurations, resolving the contradiction between achieving high efficiency at various back-off powers and managing device complexity.
3Loss of energy
If conventional N-way Doherty amplifier is used, then efficiency enhancement at high output back-off power is achieved, but performance deteriorates for higher peak-to-average power ratio signals in both gain and efficiency
Solution Approach 1:
The patent applies dynamics by implementing adaptive bias control that responds to varying input signal conditions. The power detection circuitry continuously monitors the input power level and adjusts the drain and gate bias voltages accordingly. This dynamic adjustment allows the amplifier to maintain optimal performance across a wide range of PAPR signals, resolving the contradiction between achieving high efficiency at back-off power and maintaining reliable performance for higher PAPR signals.
Data Source
AI summary
A power amplifier using N-way Doherty structure with adaptive bias supply power tracking for extending the efficiency region over the high peak-to-average power:ratio of the multiplexing modulated signals such as wideband code division multiple access and orthogonal frequency division multiplexing is disclosed. In an embodiment, present invention uses a dual-feed distributed structure to an N-way Doherty amplifier to improve the isolation between at least one main amplifier and at least one peaking amplifier and, and also to improve both gain and efficiency performance at high output back-off power. Hybrid couplers can be used at either or both of the input and output. In at least some implementations, circuit space is also conserved due to the integration of amplification, power splitting and combining.