Multi-Amplifier Doherty Topology for Wideband Backoff Efficiency
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Solution Overview
Problem
Existing Doherty amplifiers operate with high efficiency only near the center frequency and cannot handle signals with peak-to-average power ratio (PAPR) exceeding 6 dB efficiently across a wide band.
Innovation Solution
A Doherty amplifier design that includes at least four amplifiers, where the number and contribution of amplifiers to the amplification operation change based on input signal power and frequency, utilizing a combining circuit with asymmetric configurations to achieve load modulation across different power levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a general Doherty amplifier uses two amplifiers (carrier and peaking) with fixed roles, then it achieves high efficiency at backoff operation near center frequency, but it cannot handle signals with PAPR exceeding 6 dB efficiently across a wide band
Solution Approach 1:
The amplifier system is segmented into multiple independent amplifier units (first through fourth amplifiers) with different electrical length configurations. Each amplifier can be independently activated or deactivated based on operating conditions, allowing the system to handle a wider frequency band by selecting appropriate amplifier combinations while maintaining manageable individual unit complexity
Solution Approach 2:
The amplifier configuration transitions from static fixed roles to dynamic role assignment. The control circuit dynamically determines which amplifiers operate as carrier amplifiers and which operate as peaking amplifiers based on the input signal's frequency and power level, enabling adaptive optimization across different operating conditions rather than being locked into fixed configurations
2Loss of energy
If amplifier roles are fixed at center frequency, then load modulation is established at center frequency, but high-efficiency operation at backoff is achieved only near center frequency
Solution Approach 1:
Different amplifiers are designed with different local characteristics (electrical lengths of 90 degrees or 180 degrees at center frequency) to optimize performance for specific frequency ranges. The control circuit selects amplifiers with appropriate local characteristics based on the operating frequency, ensuring high efficiency is maintained across a wide frequency band rather than being limited to center frequency only
Solution Approach 2:
The system changes operating parameters (which amplifiers are active and their assigned roles) based on the input signal's frequency and power level. By dynamically adjusting amplifier electrical length selections and role assignments, the system maintains optimal efficiency across varying frequency conditions rather than being optimized for a single center frequency point
3Adaptability or versatility
If only two amplifiers are used in parallel, then the structure is simple, but the load modulation range is limited to about 6 dB PAPR
Solution Approach 1:
The amplifier system is divided into multiple independent units (four amplifiers total) that can be selectively activated. This segmentation allows the system to handle higher PAPR signals by progressively engaging additional amplifiers as needed, expanding the load modulation range beyond the 6 dB limitation of two-amplifier systems while keeping each individual amplifier unit relatively simple
Solution Approach 2:
Each amplifier unit is designed to be multi-functional, capable of operating as either a carrier amplifier or a peaking amplifier depending on the operating conditions. This universality allows four amplifiers to provide the functional equivalent of multiple Doherty stages, achieving extended PAPR handling capability without proportionally increasing overall system complexity
Data Source
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AI summary
In a Doherty amplifier (1000), the number of amplifiers contributing to an amplification operation changes depending on power of an input signal, the Doherty amplifier including at least four or more amplifiers (1, 2, 3, 4), in which order in which the amplifiers contribute to the amplification operation differs depending on a frequency of the input signal.