Doherty Impedance Inverter Layout for Wider RF Bandwidth
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Solution Overview
Problem
Conventional Doherty amplifiers face limitations in bandwidth performance due to impedance-matching components placed between the outputs of the main and peaking amplifiers and the impedance inverter, which add electrical path length and restrict the minimum phase rotation, resulting in constrained RF fractional bandwidth.
Innovation Solution
Rearranging the order of signal combining and impedance matching by removing impedance-matching elements before the impedance inverter and using an impedance inverter with an integrated distributed inductive element, such as a microstrip line, to reduce compensating phase and enhance bandwidth, allowing for scalability of signal amplification to higher powers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If impedance-matching components are placed between the outputs of the main and peaking amplifiers and the impedance inverter, then impedance matching is achieved, but the electrical path length increases and RF fractional bandwidth is constrained
Solution Approach 1:
The patent removes the impedance-matching components from their conventional position between the amplifier outputs and the impedance inverter. By extracting these components and placing them after the signal combining node, the electrical path length through the inverter is reduced, thereby increasing the minimum phase rotation and expanding the RF fractional bandwidth while still achieving impedance matching to the load.
2Reliability
If conventional Doherty amplifier configuration is used, then impedance matching is provided, but RF fractional bandwidth is limited to approximately 3%
Solution Approach 1:
The patent inverts the conventional order of operations by performing signal combining before impedance matching. Instead of matching impedances of individual amplifier outputs before combining them, the amplifiers are combined first at a signal combining node, and then a single impedance-matching component matches the combined signal to the load. This inversion eliminates the bandwidth constraints imposed by conventional configuration.
3Adaptability or versatility
If impedance-matching elements are removed before the impedance inverter, then RF fractional bandwidth increases to over 17%, but impedance matching must be achieved after signal combining
Solution Approach 1:
The patent merges the impedance matching function into a single component located after the signal combining node. Instead of having separate impedance-matching components for each amplifier output, a single matching component handles the combined signal, simplifying the overall configuration while achieving the same or better performance.
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 configuration significantly improves the RF fractional bandwidth from approximately 3% to over 17%, enabling higher power scalability while maintaining operating frequency and bandwidth performance, compared to conventional Doherty amplifiers.
Implementation Method 1
an impedance inverter with an integrated distributed inductive element in the form of a microstrip line
Data Source
Figure 1~2
Figure 3~4
Figure 5A~5B
AI summary
Apparatus and methods for a modified Doherty amplifier operating at gigahertz frequencies are described. The combining of signals from a main amplifier (132) and a peaking amplifier (138) occur prior to impedance matching of the amplifier's output to a load. An integrated distributed inductor (510) may be used in an impedance inverter to combine the signals.