Asymmetric Doherty Amplifier Shunt Reactance for Capacitance Balance
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Solution Overview
Problem
Asymmetric Doherty amplifiers face challenges in achieving compact design and broadband operation due to unequal parasitic capacitances between amplifiers, which prevent the formation of a compact impedance inverter with a 90-degree phase shift, limiting efficiency and integration capabilities in modern wireless communication networks.
Innovation Solution
The introduction of shunt reactive components, such as inductances and capacitors, between the impedance inverter and RF signal ground on one or both sides of the amplifier, balances parasitic capacitances, allowing for the formation of a compact impedance inverter that achieves a 90-degree phase shift and adjusts the characteristic impedance to match the load, eliminating the need for additional impedance matching circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If asymmetric amplifiers are used to improve efficiency for high-PAPR signals, then power efficiency is improved, but unequal parasitic capacitances prevent formation of a compact impedance inverter with 90-degree phase shift
Solution Approach 1:
A shunt reactive component is introduced as an intermediary element between the asymmetric amplifiers and the impedance inverter. This component compensates for the unequal parasitic capacitances, enabling the formation of a compact impedance inverter with the required 90-degree phase shift while maintaining the efficiency benefits of asymmetric amplifier operation.
Solution Approach 2:
The shunt reactive component changes the effective capacitance parameters seen by the impedance inverter, transforming the unequal parasitic capacitances of the asymmetric amplifiers into equal effective capacitances that enable compact 90-degree phase shift operation.
2Manufacturing precision
If traditional impedance matching circuits are added to compensate for capacitance imbalance, then phase shift accuracy is improved, but device complexity and component count increase
Solution Approach 1:
The shunt reactive component is merged with the existing amplifier and impedance inverter structures, integrating the capacitance compensation function into the existing circuit topology rather than adding separate impedance matching circuits, thereby maintaining phase shift accuracy without significantly increasing device complexity.
3Area of stationary object
If compact impedance inverter design is achieved, then area and integration density are improved, but bandwidth operation is limited
Solution Approach 1:
The shunt reactive component provides dynamic compensation that maintains the 90-degree phase shift characteristic across a broader frequency range, enabling the compact impedance inverter to operate over extended bandwidth while maintaining its compact area.
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 enables a compact, efficient Doherty amplifier design with improved bandwidth and reduced component count, facilitating integration in high-density RF power amplifiers, particularly beneficial for 5G communication standards with multiple antennas and broader frequency ranges.
Implementation Method 1
unequal parasitic capacitances between amplifiers
Implementation Method 2
shunt reactive components, such as inductances and capacitors
Implementation Method 3
impedance inverter with a 90-degree phase shift
Implementation Method 4
impedance inverter circuit connecting outputs of the first and second amplifiers
Data Source
AI summary
In an asymmetric Doherty amplifier circuit, one or more shunt reactive components are added to at least one side of an impedance inverter connecting the amplifier outputs, to reduce a capacitance imbalance between the two amplifiers caused by their different parasitic capacitances. This enables the (adjusted) parasitic capacitances to be incorporated into a quarter-wavelength transmission line, having a 90-degree phase shift, for the impedance inverter. In one embodiment, a shunt inductance is connected between the impedance inverter, on the side of the larger amplifier, and RF signal ground. The inductance is sized to resonate away substantially the excess parasitic capacitance of the larger amplifier. In another embodiment, a shunt capacitor is connected on the side of the smaller amplifier, thus raising its total capacitance to substantially equal the parasitic capacitance of the larger amplifier. In other embodiments shunt inductances and/or capacitors may be added to one or both amplifiers, and sized to effectively control a characteristic impedance of the impedance inverter.