Transistor Bias Circuit for Charge Trapping and Current Stability
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Solution Overview
Problem
Transistors, especially wide bandgap material transistors like Gallium Nitride HEMTs, experience current instability due to charge trapping and self-heating effects when switching between inactive and active states, leading to signal distortion and communication errors in applications like 5G time division duplexing.
Innovation Solution
A circuit and method that selectively outputs a control signal with different voltage levels to bias a transistor, transitioning from a first voltage level to a second and then a third level over time, to compensate for trapping and self-heating effects, ensuring consistent current flow and reducing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the transistor is fully turned off in the first state, then trapping effects are reduced, but noise increases
Solution Approach 1:
The patent applies dynamics by transitioning the transistor through multiple voltage levels (second and third voltage levels) rather than maintaining a static off-state. The control signal dynamically changes over time, first applying a second voltage level to clear trapped charges, then transitioning to a third voltage level for stable operation, thereby reducing trapping effects while controlling noise through controlled transitions rather than abrupt switching
Solution Approach 2:
The patent applies preliminary action by applying a second voltage level before the third voltage level to pre-clear trapped charges from the transistor. This preliminary step prepares the transistor for stable operation at the third voltage level, preventing trapping effects that would otherwise occur during normal switching operations
2Productivity
If the transistor is switched between inactive and active states, then signal transmission is enabled, but current instability occurs due to charge trapping and self-heating
Solution Approach 1:
The patent applies preliminary action by applying a second voltage level before the final operating voltage level to pre-clear trapped charges and prepare the transistor for stable operation. This preliminary step ensures that when the transistor transitions to the active state, it starts from a known stable condition, reducing current instability caused by charge trapping effects
Solution Approach 2:
The patent applies dynamics by implementing a multi-stage voltage transition process that adapts to the transistor's state. The control signal dynamically progresses through different voltage levels based on timing conditions, allowing the system to respond to the transistor's thermal and charge state, thereby maintaining current stability during switching operations
3Ease of operation
If a conventional biasing method is used, then the transistor operates at a fixed point, but current varies after switching due to trapping and self-heating effects
Solution Approach 1:
The patent applies dynamics by replacing the static fixed operating point with a dynamic multi-level voltage transition process. The control signal adapts its waveform based on timing conditions, transitioning through different voltage levels to account for trapping and self-heating effects, thereby ensuring reproducible current operation while maintaining ease of control through automated timing-based switching
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 stabilizes the current through the transistor, minimizing signal distortion and communication errors by compensating for trapping and self-heating effects, thereby improving the reproducibility of AC signal amplification.
Implementation Method 1
due to effects like charge trapping or, immediately after transitioning to the second transistor state a different, for example lower current may result
Implementation Method 2
Also other effects like self-heating may influence the current
Data Source
Figure 1~3
Figure 4~5
Figure 6
AI summary
A circuit for biasing a transistor (13) is provided. The circuit includes an output terminal (12) configured to be coupled to a gate terminal (14) of the transistor and circuitry (11). In a first state, the circuitry (11) is configured to output a control signal at a first voltage level for setting the transistor (13) to a first transistor state. In a second state, the circuitry (11) is configured to first output the control signal at a second voltage level different from the first voltage level following by changing the control signal from the second voltage level towards a third voltage level different from the first and second voltage level over time.