Class-C Power Amplifier Harmonic Impedance Optimization
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Solution Overview
Problem
Class-C and class-B power amplifiers face challenges in achieving broader bandwidths while maintaining high efficiency, with class-C amplifiers having narrow bandwidths and class-B amplifiers operating at lower efficiency, and both requiring short-circuiting of higher order harmonics to increase efficiency.
Innovation Solution
A class-C power amplifier design with a conduction angle less than π(rad) is implemented, where the load impedance of the fundamental wave and 2nd harmonic are set as functions of the conduction angle, and the relationship between R1 and X1 is adjusted to achieve high efficiency over broader bandwidths by setting R1=Vdc/Imax·{1−cos(θo/2)}/{θo/2−sin(θo)/2} and X2/X1=−{θo/2−sin(θo)/2}/{sin(θo/2)−sin(1.5·θo)/3}, allowing for efficient operation similar to class-B amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If class-C power amplifier is operated with high efficiency by short-circuiting load impedance for higher order harmonics, then drain efficiency is improved, but bandwidth becomes narrow
Solution Approach 1:
The patent changes the load impedance parameters for harmonics from short-circuit (class-C) to non-zero values. Specifically, it sets the load impedance for the 2nd harmonic to a predetermined non-zero value while maintaining the load impedance for the fundamental wave, thereby achieving both high efficiency and broad bandwidth through parameter optimization
Solution Approach 2:
The patent introduces dynamic adjustment of load impedance for harmonics across different frequency bands. By making the harmonic load impedance frequency-dependent rather than fixed at zero, the amplifier can adapt to different operating conditions and maintain performance across broader bandwidths
2Adaptability or versatility
If class-B power amplifier is used to achieve broader bandwidths, then bandwidth is improved, but drain efficiency becomes lower than class-C
Solution Approach 1:
The patent optimizes the load impedance parameters for harmonics to achieve a balance between class-B and class-C operation characteristics. By setting specific non-zero values for harmonic load impedances, it achieves broader bandwidths comparable to class-B while maintaining higher drain efficiency closer to class-C performance
3Loss of energy
If load impedance for higher order harmonics is short-circuited to increase efficiency, then drain efficiency is improved, but the degree of difficulty in achieving broader bandwidths increases
Solution Approach 1:
The patent simplifies the design by establishing predetermined relationships for load impedance parameters. Specifically, it sets the load impedance for the 2nd harmonic to a predetermined non-zero value and defines the relationship between fundamental wave and harmonic load impedances, thereby reducing design complexity while achieving both high efficiency and broad bandwidth
Data Source
AI summary
According to one embodiment, a class-C power amplifier includes an amplifying element whose power supply voltage is expressed as Vdc and whose maximum current is expressed as Imax, a conduction angle θo of the amplifying element being less than π(rad), and load impedance of a fundamental wave being expressed as Z1=R1+j·X1 and load impedance of a 2nd harmonic being expressed as Z2=R2+j·X2 which are observed from a dependent current source of an equivalent circuit of the amplifying element, wherein a relationship between variables X1 and R1 is set to −R1<=X1<=R1, variable R1 is set to R1=Vdc/Imax·π·{1−cos(θo/2)}/{θo/2−sin(θo)/2}, and variable X2/X1 is set to X2/X1=−{θo/2−sin(θo)/2}/{sin(θ/2)−sin(1.5·θo)/3}, or each of the variables is set thereto so as to become equal substantially.