GaN Power Amplifier Input Harmonic Termination Circuit
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Solution Overview
Problem
Designing broadband power amplifiers using GaN-based devices is challenging due to nonlinear input capacitance generating harmonics and intermodulation distortion, low drain-source capacitance, and difficulty in tuning for high fractional bandwidth and efficiency, especially with conventional output impedance matching circuits that require high D2 inductance and are inefficient.
Innovation Solution
The implementation of an input-side harmonic termination circuit with a bondwire connection and RF capacitor, and an output-side harmonic termination circuit with integrated capacitance and inductance, reduces D2 inductance and controls second harmonic impedance across a wide fractional bandwidth, enhancing efficiency and linearity through equivalent shunt capacitance that increases drain-source capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional output impedance matching circuits are used, then broadband amplification can be achieved, but efficiency drops significantly due to high D2 inductance requirements
Solution Approach 1:
The patent changes the impedance parameters at the second harmonic frequency by introducing harmonic termination circuits that provide specific impedance values (e.g., open circuit or short circuit conditions) at the second harmonic. This allows the circuit to maintain broadband amplification capability while reducing the required D2 inductance value, thereby improving efficiency by reducing energy losses associated with high inductance.
2Loss of energy
If GaN-based devices are used to achieve high power density, then efficiency improves, but nonlinear input capacitance generates harmonics and intermodulation distortion
Solution Approach 1:
The patent converts the harmful effect of nonlinear input capacitance generating second harmonic frequencies into a beneficial effect by deliberately designing harmonic termination circuits that control the second harmonic impedance. The second harmonic energy, which would normally cause distortion and inefficiency, is now controlled to improve overall amplifier performance, linearity, and efficiency simultaneously.
3Adaptability or versatility
If broadband operation is achieved with fractional bandwidth over 20 percent, then multi-band amplification is enabled, but harmonic control becomes increasingly difficult
Solution Approach 1:
The patent segments the frequency spectrum by treating the second harmonic frequency as a separate control target from the fundamental broadband operation. By introducing dedicated harmonic termination circuits specifically tuned to control second harmonic impedance, the patent enables broadband operation (fractional bandwidth > 20%) while managing harmonic control independently, thus reducing the complexity of simultaneous broadband and harmonic control.
Data Source
AI summary
Embodiments of RF amplifiers and packaged RF amplifier devices each include a transistor with a drain-source capacitance that is relatively low, an input impedance matching circuit, and an input-side harmonic termination circuit. The input impedance matching circuit includes a harmonic termination circuit, which in turn includes a first inductance (a first plurality of bondwires) and a first capacitance coupled in series between the transistor output and a ground reference node. The input impedance matching circuit also includes a second inductance (a second plurality of bondwires), a third inductance (a third plurality of bondwires), and a second capacitance coupled in a T-match configuration between the input lead and the transistor input. The first and second capacitances may be metal-insulator-metal capacitors in an integrated passive device.