Wideband Doherty Power Amplifier for VHF Efficiency and Heat Control
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Solution Overview
Problem
Current power amplifiers, such as those used in aircraft radios, face inefficiencies and heat dissipation issues due to their narrow band operation, limiting their application in wideband frequencies like 118 MHz to 137 MHz, where they cannot utilize Doherty power amplifiers effectively.
Innovation Solution
A wideband Doherty power amplifier configuration using a quadrature coupler and impedance transformer with lumped element impedance transformation circuitry, allowing the carrier and peak amplifiers to operate efficiently across a wide frequency range by modifying load impedance and phase shift compensation, enabling efficient power amplification in aircraft radios like VHF VDL Mode2 transmitters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If class A/AB power amplifiers are used for wideband operation, then linearity is improved, but power efficiency deteriorates and heat dissipation increases
Solution Approach 1:
The power amplifier is segmented into two separate amplifiers: a carrier amplifier that operates continuously and a peak amplifier that operates only when needed. This segmentation allows each amplifier to be optimized for its specific function, with the carrier amplifier maintaining linearity and the peak amplifier providing efficiency during high-power conditions.
Solution Approach 2:
The system dynamically switches between different amplifier configurations based on the input signal power level. At low power levels, only the carrier amplifier operates. When the signal exceeds a threshold, the peak amplifier is activated to share the amplification load, dynamically adapting the system's efficiency characteristics to match the operational requirements.
2Loss of energy
If Doherty power amplifier configuration is used, then power efficiency is improved, but bandwidth is limited to narrow band operation
Solution Approach 1:
The patent transforms the fixed narrowband Doherty configuration into a wideband system by making the coupling coefficient of the quadrature coupler a variable parameter that changes with frequency. This parameter change allows the amplifier to maintain proper operation across a wide frequency range (118-137 MHz) while preserving the efficiency benefits of the Doherty architecture.
Solution Approach 2:
The system dynamically adjusts the coupling coefficient of the quadrature coupler based on the operating frequency. This dynamic adjustment compensates for frequency variations and maintains optimal performance across the wide bandwidth, enabling the Doherty configuration to operate efficiently over the entire VHF spectrum.
3Device complexity
If conventional power amplifiers are used in aircraft radios, then simplicity is maintained, but heat dissipation increases requiring bulky heat sinks and active cooling
Solution Approach 1:
The patent converts the harmful effect of high peak power requirements into a benefit by using the peak amplifier only when necessary. The carrier amplifier handles continuous low-power operation efficiently, while the peak amplifier is activated only during high-power peaks, converting what would be continuous heat generation into intermittent, manageable heat events that require less cooling infrastructure.
Data Source
AI summary
A wideband power amplifier is presented. The wideband power amplifier configured to be coupled to a load having an impedance ZL, where the wideband power amplifier comprises: a quadrature coupler; a carrier amplifier coupled to the quadrature coupler; a peak amplifier coupled to the quadrature coupler; wherein the carrier amplifier saturates at an input power level lower than the input power level at which the peak amplifier saturates; wherein each of the carrier amplifier and the peak amplifier has a termination impedance of approximately Ropt, where Ropt is the optimum impedance at which the carrier amplifier and the peak amplifier will deliver rated max powers; a impedance transformer, coupled to the carrier amplifier having a characteristic impedance of 2*Ropt; an impedance transformer, coupled to the peak amplifier and the impedance transformer; wherein the impedance transformer is configured transform a load impedance ZL to 2*Ropt.