Semiconductor Amplifier Bias Circuit for Second-Harmonic Open Impedance
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Solution Overview
Problem
Existing semiconductor amplifiers face challenges in achieving high-efficiency operation by controlling harmonics, particularly in making the load impedance near-open at the second harmonic frequency without affecting the fundamental signal, which is crucial for maintaining power added efficiency across the desired frequency band.
Innovation Solution
The semiconductor amplifier incorporates an output bias circuit with a third transmission line, a grounded shunt capacitor, and a specific electrical length configuration to ensure near-open impedance at the second harmonic frequency while maintaining near-open impedance at the fundamental frequency, utilizing transmission lines with varying characteristic impedances and electrical lengths to achieve this balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bias circuit with a transmission line of 90° electrical length and grounded shunt capacitor is used, then the impedance at fundamental frequency is near-open, but the impedance at second harmonic becomes near-short
Solution Approach 1:
The bias circuit transmission line is divided into two segments: a first transmission line with 45° electrical length and a second transmission line with 45° electrical length. This segmentation allows the total 90° electrical length to be distributed, creating different impedance characteristics at fundamental and second harmonic frequencies. The first transmission line provides the primary bias function while the second transmission line contributes to achieving near-open impedance at the second harmonic.
2Loss of energy
If the bias circuit is connected to control harmonics, then high-efficiency operation is achieved, but the matching circuit at fundamental signal is affected
Solution Approach 1:
A capacitor is introduced as an intermediary element connected between the connection point of the bias circuit and the matching circuit. This capacitor has an impedance that is small at the fundamental frequency (allowing the bias circuit to be effectively connected) but large at the second harmonic frequency (isolating the harmful impedance effect). This intermediary component allows the bias circuit to control harmonics while preventing degradation of the fundamental signal matching.
3Device complexity
If a single transmission line bias circuit is used, then circuit simplicity is maintained, but impedance control at both fundamental and second harmonic frequencies cannot be achieved simultaneously
Solution Approach 1:
The single transmission line is segmented into two transmission lines with specific electrical lengths (both 45° at fundamental frequency). This segmentation enables the bias circuit to present different impedance characteristics at fundamental and second harmonic frequencies, achieving near-open impedance at the second harmonic while maintaining near-open impedance at the fundamental frequency, without significantly increasing circuit complexity.
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 effectively maintains high power added efficiency by ensuring the load impedance for the second harmonic is near-open, even when the bias circuit is connected, facilitating efficient operation across the desired frequency range.
Implementation Method 1
the first transmission line has a first electrical length EL1 which is 90° or less at the upper limit frequency fH... the second transmission line has a second electrical length EL2 which is 45° or more and less than 90° at the center frequency fC
Implementation Method 2
a grounded shunt capacitor connected to one end part of the second transmission line... the bias circuit has a near-short impedance at the second harmonic frequency because an electrical length becomes approximately 180°
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A semiconductor amplifier includes a semiconductor amplifying element (14), an output terminal (18), an output matching circuit (20), and an output bias circuit (34). The output matching circuit (20) includes a bonding wire (15), a first transmission line (16), and a second transmission line (21). The other end part of the first transmission line (16) is connected to one end part of the second transmission line (21).The output bias circuit (34) includes a third transmission line (30) having an electrical length of approximately 90° at a center frequency, a grounded shunt capacitor (32), and a power supply terminal (39). The third transmission line (30) includes one end part and the other end part connected to the grounded shunt capacitor (32). The one end part of the third transmission line (30) is connected to the second transmission line (21) at a position where an electrical length is approximately 45° from the one end part of the second transmission line (21) at the center frequency.