Doherty Amplifier Phase Synthesis for Inductive Load Suppression
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Solution Overview
Problem
The power amplifier described in Patent Literature 1 experiences a decrease in efficiency due to a strong inductive load connected to the output terminal of the auxiliary amplifier during load modulation from the backoff point to saturation output, which cannot be suppressed effectively.
Innovation Solution
A Doherty amplifier design featuring first and second amplifying elements with specific phase differences and transmission lines, where the first and second transmission lines have equal characteristic impedance, and the phase difference between the signals is configured to avoid matching the electrical length difference, allowing for different phase synthesis and reducing inductivity through capacitance generated by the phase difference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a transmission line is connected to the output terminal of the auxiliary amplifier, then the amplifier can operate at high efficiency at large backoff points, but a strong inductive load cannot be suppressed during load modulation from backoff point to saturation output
Solution Approach 1:
The patent applies asymmetry by setting different electrical lengths for the first and second transmission lines. The first transmission line has an electrical length of 70-90 degrees while the second has 90-180 degrees. This asymmetric configuration creates different phase shifts for the main and auxiliary amplifier signals, which transforms the strong inductive load into a manageable load condition during load modulation, thereby suppressing the harmful inductive load effect while maintaining high efficiency operation
Solution Approach 2:
The patent changes the electrical length parameter of the transmission lines to specific ranges (70-90 degrees for the first line, 90-180 degrees for the second line). By optimizing these parameter values, the patent achieves proper phase relationship between the amplifier outputs during load modulation, which transforms the inductive load characteristic and enables high efficiency operation across the modulation range from backoff point to saturation output
2Device complexity
If the phase difference between first and second signals equals the electrical length difference between transmission lines, then simple phase relationship is achieved, but inductivity increases reducing power added efficiency
Solution Approach 1:
The patent optimizes the electrical length parameters of the transmission lines to specific ranges (70-90 degrees and 90-180 degrees) to achieve the desired phase relationship. By carefully selecting these parameter values, the patent creates a phase difference that transforms inductive load into a more favorable load condition, thereby improving power added efficiency while maintaining manageable system complexity
Solution Approach 2:
The patent converts the potentially harmful inductive load effect into a beneficial condition by utilizing the phase difference created by the asymmetric transmission line lengths. The phase relationship, when properly configured within the specified electrical length ranges, transforms the inductive reactance into a condition that improves power added efficiency, effectively converting a harmful factor into a beneficial one
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 enables the Doherty amplifier to operate with high efficiency from the backoff point to saturation output by minimizing inductivity and maximizing power added efficiency.
Implementation Method 1
a phase difference between a first signal and a second signal is configured to be selected so as not to be equal to a difference in electrical length between the second transmission line and the first transmission line
Implementation Method 2
the electrical length of the first transmission line is within a range from 70 degrees to 90 degrees, the electrical length of the second transmission line is within a range from 90 degrees to 180 degrees
Implementation Method 3
The inductivity generated during load modulation from the backoff point to the saturation output is reduced by capacitance generated in a load by the phase difference between the first signal and the second signal
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A Doherty amplifier (1) includes: a first amplifying element (5) to amplify a first signal; a second amplifying element (6) to amplify a second signal having a phase difference with the first signal; a first transmission line (7) connected to an output terminal of the first amplifying element (5); and a second transmission line (8) connected to an output terminal of the second amplifying element (6), wherein the first transmission line (7) and the second transmission line (8) are equal to each other in characteristic impedance, the phase difference between the first signal and the second signal is not equal to a difference in electrical length between the second transmission line (8) and the first transmission line (7), and the first signal having passed through the first transmission line (7) and the second signal having passed through the second transmission line (8) are subjected to different phase synthesis.