RF Power Transistor Output Pre-Match for Wideband Harmonic Control
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Solution Overview
Problem
Designing RF semiconductor devices with high instantaneous signal bandwidth (ISBW) is challenging due to low frequency resonance caused by bondwire inductances, which limit the devices' performance in wideband applications, especially with GaN transistors that have low drain-source capacitance, requiring large output shunt inductance and posing thermal management and harmonic control issues.
Innovation Solution
The solution involves splitting the shunt inductance across a wire array and integrated passive device (IPD) printed coils, introducing an additional intermediate shunt capacitance for harmonic control, and implementing an envelope frequency termination circuit with high-value capacitance to decouple low frequency resonance, thereby improving thermal management and increasing ISBW.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If bondwires are used to interconnect output circuit components, then the device can be manufactured with standard bonding techniques, but the bondwire inductances cause low frequency resonance that limits instantaneous signal bandwidth
Solution Approach 1:
The patent extracts the harmful inductance from the bondwire interconnections by removing the bondwire from the signal path between the power amplifier and the output matching circuit. This is achieved by using a flip-chip mounted power amplifier with direct solder ball connections to the substrate, eliminating the bondwire inductance that causes low frequency resonance and limiting instantaneous signal bandwidth.
Solution Approach 2:
The patent introduces a substrate as an intermediary between the power amplifier and the output matching circuit. The substrate provides direct electrical connection through solder balls, acting as a mediator that eliminates the need for bondwires and their associated inductances, thereby resolving the low frequency resonance issue while maintaining manufacturability.
2Reliability
If large output shunt inductance is used to compensate for low drain-source capacitance in GaN transistors, then the transistor can operate at fundamental frequencies, but thermal management becomes difficult and power dissipation increases
Solution Approach 1:
The patent segments the output matching circuit into separate functional blocks: the power amplifier, the output matching circuit, and the low pass filter are implemented as distinct components. This segmentation allows each component to be optimized independently, with the power amplifier focusing on fundamental frequency operation while the low pass filter handles harmonic termination, thereby reducing thermal issues associated with large shunt inductors.
Solution Approach 2:
The patent implements dynamic harmonic termination through a low pass filter that adaptively terminates harmonics based on the operating conditions. This dynamic approach allows the system to maintain fundamental frequency operation while efficiently managing thermal characteristics by terminating harmonics only when necessary, rather than using static large shunt inductors that continuously dissipate power.
3Area of stationary object
If impedance matching circuits are integrated within the same package, then device compactness is achieved, but low frequency resonance from bondwire inductances degrades performance
Solution Approach 1:
The patent extracts the harmful bondwire inductance from the integrated package by using direct solder ball connections on the substrate. This eliminates the low frequency resonance that would otherwise limit instantaneous signal bandwidth, while the impedance matching circuits remain integrated within the same package through direct mounting of the power amplifier and matching components on the substrate.
Solution Approach 2:
The patent replaces the mechanical bondwire interconnection system with a direct solder ball mounting system. This substitution eliminates the inductance introduced by bondwires while maintaining the compact integrated package structure, thereby resolving the low frequency resonance issue without sacrificing integration benefits.
4Loss of energy
If harmonic termination is implemented, then RF amplifier efficiency is improved, but device complexity increases with additional circuits
Solution Approach 1:
The patent merges the harmonic termination function with the output matching circuit by implementing a low pass filter that serves dual purposes: matching the output impedance and terminating harmonics. This integration achieves efficient harmonic termination and reduced power dissipation without significantly increasing device complexity, as the same circuit elements perform multiple functions.
Solution Approach 2:
The low pass filter in the output matching circuit is designed to perform multiple functions simultaneously: impedance matching at the fundamental frequency and harmonic termination at higher frequencies. This multi-functionality reduces the need for separate harmonic termination circuits, thereby maintaining device compactness and minimizing additional complexity while achieving improved power efficiency.
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 approach enhances the RF amplifier's bandwidth and efficiency by reducing thermal issues and maintaining compensation bandwidth at fundamental frequencies while minimizing RF energy at the RF cold point, leading to improved drain efficiency and reduced power dissipation.
Implementation Method 1
The shunt capacitance and the shunt inductance form a series resonant circuit having a resonant frequency in proximity to a center operating frequency of the amplifier
Implementation Method 2
An RF cold point is present between the first and second shunt inductors
Implementation Method 3
implementing an envelope frequency termination circuit with high-value capacitance to decouple low frequency resonance
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
Embodiments of an RF amplifier include a transistor (120, 220) with a control terminal and first and second current carrying terminals, and a shunt circuit coupled between the first current carrying terminal and a ground reference node. The shunt circuit is an output pre-match impedance conditioning shunt circuit, which includes a first shunt inductance (134, 234, 434), a second shunt inductance (135, 135', 235 435, 935, 935'), and a shunt capacitor (142, 142', 342, 442) coupled in series. The first shunt inductance (134, 234, 434) comprises a plurality of bondwires coupled between the first current carrying terminal and the second shunt inductance (135, 135', 235 435, 935, 935'), and the second shunt inductance (135, 135', 235 435, 935, 935') comprises an integrated inductor coupled between the first shunt inductance (134, 234, 434) and a first terminal of the shunt capacitor (142, 142', 342, 442). The shunt capacitor (142, 142', 342, 442) is configured to provide capacitive harmonic control of an output of the transistor (120, 220).