Balanced RF Power Amplifier With Dynamic Impedance Modulation
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Solution Overview
Problem
Conventional radio frequency power amplifiers experience efficiency degradation during power back-off, limiting their operational bandwidth and efficiency in applications requiring high efficiency over a wide bandwidth, such as electronic warfare systems and new mobile communication systems.
Innovation Solution
A radio frequency power amplifier system with a balanced amplifier design that includes an input quadrature coupler, an output quadrature coupler, and two amplifiers, where a radio frequency control signal is used to modify the impedance at the amplifiers' outputs by reflecting an amplified control signal back into the output coupler, eliminating the need for an auxiliary amplifier and allowing for phase and amplitude adjustments to maintain efficiency across varying power and frequency conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional radio frequency power amplifier is used, then the amplifier can operate at peak power efficiently, but the efficiency degrades quickly as output power is reduced (power back-off)
Solution Approach 1:
The amplifier is divided into two independent but synchronized amplifier units, each handling a portion of the signal. This segmentation allows each amplifier to operate more efficiently across a broader range of power levels, resolving the contradiction between maintaining efficiency during power back-off and expanding operational bandwidth.
Solution Approach 2:
The system dynamically adjusts the operating state of the amplifiers by introducing a control signal that modifies the impedance at the amplifier outputs. This dynamic adjustment enables the amplifiers to maintain high efficiency across varying power levels and bandwidth conditions, rather than being fixed at peak power optimization.
2Loss of energy
If a Doherty power amplifier is used, then efficiency is improved over conventional balanced amplifiers, but the operational bandwidth is limited
Solution Approach 1:
The amplifier design incorporates universal components that can function effectively across multiple operating conditions and bandwidths. The two amplifiers are designed with identical characteristics and can operate independently or in combination, providing universal functionality that extends bandwidth while maintaining the efficiency benefits of Doherty architecture.
Solution Approach 2:
The system uses dynamic control signals to adjust the impedance matching and operating point of the amplifiers in real-time, enabling the amplifier to maintain high efficiency across a wider bandwidth compared to traditional Doherty designs which are optimized for narrowband operation.
3Loss of energy
If an auxiliary amplifier is added to extend efficiency range (as in GB2533824), then efficiency over wider input power range is achieved, but the device complexity increases and control becomes difficult
Solution Approach 1:
The control signal is generated internally by the amplifier system itself using the same input signal, eliminating the need for external auxiliary amplifiers or complex control circuits. The system serves its own control needs through signal routing and impedance modulation, reducing device complexity while maintaining efficiency benefits.
Solution Approach 2:
The control function is merged with the main amplification function by using the same amplifier units for both purposes. The amplifiers process both the main signal and generate control signals through their operation, combining multiple functions into a unified structure that reduces overall system complexity.
4Loss of energy
If phase offset control is used to extend power back-off range (Chireix amplifier), then efficiency is improved, but phase compensation networks are required which limit operational bandwidth
Solution Approach 1:
Instead of using fixed phase compensation networks that limit bandwidth, the system employs dynamic impedance modulation through control signals that adapt to the operating conditions. This dynamic approach maintains efficiency benefits of phase control while extending operational bandwidth by eliminating the bandwidth-limiting compensation networks.
Solution Approach 2:
The system changes the impedance parameters dynamically through control signals rather than using fixed phase compensation networks. By modulating the impedance at the amplifier outputs through controlled signal injection, the system achieves efficiency improvement across a wider bandwidth without the bandwidth limitations imposed by fixed compensation circuits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances the amplifier's efficiency and operational bandwidth by dynamically adjusting the impedance at the amplifiers' outputs, maintaining high efficiency even at reduced power levels and across a wide frequency range, without the need for an auxiliary amplifier, thus addressing the limitations of existing Doherty and Chireix amplifiers.
Implementation Method 1
a signal reflector connected to the second output of the output quadrature coupler arranged to reflect the amplified control signal back to the second output of the output quadrature coupler
Data Source
AI summary
A balanced amplifier system having input and output quadrature couplers or equivalents thereof and two amplifiers there between. An RF signal is presented to a first input of an input quadrature coupler such that an amplified RF signal is output at a first output of the output quadrature coupler. A RF control signal is presented to a second input of the quadrature coupler such that an amplified control signal is outputted at the other output of the output quadrature coupler. The system is configured to reflect the amplified signal back into the second port of the output quadrature coupler in order to vary an impedance seen by the amplifiers of the balanced amplifier.