Class-AB Power Amplifier Harmonic Load Matching for Wideband Efficiency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Class-AB power amplifiers face challenges in achieving high linearity and efficiency over broader bandwidths due to the difficulty in load impedance matching for higher order harmonics, which affects their efficiency and linearity compared to class-A and class-B amplifiers.
Innovation Solution
The class-AB power amplifier employs a conduction angle greater than π(rad) and specific relationships between load impedances for fundamental and harmonic waves, including R1 and X2/X1 ratios, to achieve high linearity and efficiency over broader bandwidths, using a Field Effect Transistor (FET) as the amplifying element and optimizing the output side matching circuit for harmonic treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If load impedance matching for higher order harmonics is performed to improve efficiency in class-AB operation, then efficiency increases, but bandwidth becomes narrower
Solution Approach 1:
The patent changes the load impedance parameters for higher order harmonics using specific formulas: R2 = k·R1 and X2 = -k·X1, where k is a positive constant. This parameter transformation allows the amplifier to achieve high efficiency (comparable to class-B) while maintaining broader bandwidths, resolving the traditional trade-off between efficiency and bandwidth in class-AB operation
Solution Approach 2:
The patent dynamically adjusts the load impedance for harmonics based on the fundamental wave impedance characteristics. By making the harmonic load impedance proportional to the fundamental impedance through the constant k, the system adapts to different operating conditions while maintaining both high efficiency and broad bandwidth performance
2Adaptability or versatility
If class-B operation is used to achieve broader bandwidths, then bandwidth increases, but linearity deteriorates
Solution Approach 1:
The patent applies different quality characteristics to different parts of the signal spectrum. The fundamental wave receives standard amplification treatment, while higher order harmonics receive specialized impedance matching (R2 = k·R1, X2 = -k·X1). This local differentiation allows the amplifier to achieve class-B-like bandwidth while maintaining class-AB linearity through selective harmonic treatment
3Reliability
If class-A operation is used to maintain high linearity, then linearity is preserved, but efficiency decreases to around 50%
Solution Approach 1:
The patent applies partial class-AB operation with conduction angle greater than π but less than 2π, combining elements of both class-A and class-B operations. By operating in this intermediate regime and applying specific harmonic impedance matching, the amplifier achieves better than 50% efficiency while maintaining high linearity, exceeding the limitations of traditional class-A operation
Data Source
AI summary
According to an embodiment, a class-AB 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 more than π(rad) and less than 2·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(θo/2)−sin(1.5·θo)/3}, or each of the variables is set thereto so as to become equal substantially.