Power Transistor Output Match Network Bypassing Low Frequency Gain Peak
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Solution Overview
Problem
RF power transistors with inductive shunt output impedance matching networks experience undesired low frequency gain peaks, leading to high peak drain voltages that can exceed the breakdown voltage, causing device overstress and performance issues, particularly in digital predistortion systems.
Innovation Solution
A power circuit with an output match network and a bypass network, where the bypass network is coupled in parallel with the blocking capacitor to attenuate the low frequency gain peak while maintaining the high quality factor RF path, thereby reducing peak drain voltage without affecting high frequency performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a blocking capacitor is used in the output match network to block DC, then DC blocking is achieved, but a low frequency gain peak is created that causes high peak drain voltages and device overstress
Solution Approach 1:
The output match network is segmented into two separate networks: a first output match network containing the blocking capacitor for DC blocking, and a second output match network without the blocking capacitor to provide a low frequency path. This segmentation allows each network to be optimized for its specific function without the harmful interactions caused by the single network configuration.
Solution Approach 2:
A transformer is introduced as an intermediary component to couple the first and second output match networks. The transformer enables the low frequency signal path to bypass the blocking capacitor while maintaining proper impedance matching and DC blocking functionality, thereby eliminating the low frequency gain peak without compromising the DC blocking function.
2Quantity of substance
If the value of the blocking capacitor is increased to move the gain peak to a lower frequency region, then the gain peak frequency is reduced, but video bandwidth is severely impacted and peak voltages at the device drain are not effectively reduced
Solution Approach 1:
The signal path is divided into two separate match networks with different capacitor configurations. The first network maintains the original blocking capacitor value for proper DC blocking without affecting video bandwidth, while the second network provides an alternative low frequency path that avoids the gain peak issue entirely.
3Object-affected harmful factors
If low frequency input trap circuits are used to mitigate low frequency gain peaks, then gain peak attenuation is achieved, but system instabilities are introduced and video bandwidth is limited
Solution Approach 1:
A transformer is used as an intermediary to couple two separate output match networks, providing a stable low frequency signal path that bypasses the blocking capacitor without introducing the instabilities associated with traditional input trap circuits. This approach maintains system stability while effectively mitigating the low frequency gain peak.
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
The bypass network effectively reduces the low frequency gain peak, preventing device overstress and ensuring proper operation by keeping peak drain voltage below the breakdown voltage while maintaining high frequency performance.
Implementation Method 1
The output match network is operable to provide a range of impedance matching over a signal bandwidth and a low frequency gain peak outside the signal bandwidth which corresponds to a low frequency resonance of the high quality factor RF path
Implementation Method 2
a blocking capacitor which forms part of a high quality factor RF path of the output match network
Data Source
AI summary
A power circuit includes a power device, an output match network and a bypass network. The output match network is coupled to an output of the power device and includes a blocking capacitor which forms part of a high quality factor RF path of the output match network. The output match network is operable to provide a range of impedance matching over a signal bandwidth and a low frequency gain peak outside the signal bandwidth which corresponds to a low frequency resonance of the high quality factor RF path. The bypass network is coupled in parallel with the blocking capacitor of the output match network. The bypass network is operable to attenuate the low frequency gain peak while maintaining the high quality factor RF path.