Dynamic Biasing Circuit for MOS Transistor Leakage and On-Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current power management systems in electronic devices fail to effectively minimize static consumption by leakage currents in power transistors, as existing methods for reducing leakage currents either increase resistance in the on-state or require additional external voltage sources, which are not commercially viable.
Innovation Solution
A dynamic biasing circuit for MOS power transistors that includes a switch to forward bias the substrate diode when the transistor is on and reverse bias it when off, using a diode stack with transistors of chosen conductivity and threshold voltages, allowing for adjustable biasing without additional external voltage sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If reverse body biasing is applied to reduce leakage current, then leakage current decreases, but threshold voltage increases causing higher resistance in on-state
Solution Approach 1:
The patent applies dynamic body biasing where the substrate voltage is dynamically adjusted based on the transistor state. A control circuit monitors the transistor operation and applies reverse body bias (higher substrate voltage) when the transistor is off to reduce leakage, and forward body bias (lower substrate voltage) when the transistor is on to maintain low resistance. This dynamic adjustment resolves the contradiction by adapting the biasing condition to the operational state.
Solution Approach 2:
The patent changes the substrate voltage parameter dynamically to achieve different biasing conditions. By varying the substrate voltage level based on transistor state, the system optimizes both leakage reduction and on-state conductivity. The control circuit adjusts this parameter in real-time, allowing the same transistor to operate with different threshold voltages depending on whether it needs to be off (low leakage) or on (low resistance).
2Reliability
If forward body biasing is applied to reduce resistance in on-state, then resistance decreases, but leakage current increases
Solution Approach 1:
The system dynamically switches between forward body bias and reverse body bias based on transistor operation state. When the transistor is on, forward body bias (lower substrate voltage) is applied to minimize resistance and maximize current flow. When the transistor transitions to off state, the control circuit switches to reverse body bias to minimize leakage. This dynamic switching resolves the contradiction by applying the appropriate biasing mode at the appropriate time.
Solution Approach 2:
The substrate voltage parameter is changed dynamically to achieve optimal performance in both on and off states. The control circuit adjusts the substrate voltage level based on detected transistor state, applying forward bias (lower voltage) for on-state operation and reverse bias (higher voltage) for off-state operation. This parameter adjustment resolves the contradiction between low resistance and low leakage requirements.
3Object-generated harmful factors
If dynamic biasing circuit is implemented, then both leakage reduction and low on-state resistance are achieved, but device complexity increases
Solution Approach 1:
The dynamic biasing circuit is designed to be self-regulating, using the transistor's own operational state to control the biasing condition. The control circuit detects the transistor state and automatically adjusts the substrate voltage accordingly, without requiring external intervention or complex control logic. This self-service approach minimizes the added complexity while achieving the dual benefit of leakage reduction and low on-state resistance.
Solution Approach 2:
The dynamic biasing circuit is designed to work with transistors of various sizes and configurations, providing a universal solution that can be applied across different power transistor implementations. The control circuit uses general principles to adjust substrate voltage, making the solution adaptable to different transistor dimensions and technology nodes without requiring specific customization for each case.
4Power
If transistor size is increased to handle higher current, then current handling capacity increases, but leakage current increases proportionally
Solution Approach 1:
The patent applies reverse body bias by increasing the substrate voltage relative to the source, which increases the threshold voltage of the transistor. This parameter change effectively reduces the leakage current component that scales with transistor size, while the forward body bias capability maintains the current handling capacity when the transistor is on. The dynamic adjustment of this parameter resolves the contradiction between power handling and leakage.
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 solution achieves a balance between low leakage in the off-state and low resistance in the on-state, improving conductivity by up to 20% while managing power dissipation, and can be used across a range of transistor sizes without specific design for each.
Implementation Method 1
a first switch configured to link the substrate to a current source which forward biases the intrinsic source-substrate diode of the transistor
Implementation Method 2
a second switch arranged to link the substrate to a reference voltage so that the intrinsic source-substrate diode of the transistor is reverse biased or biased to zero voltage, when the gate voltage of the power transistor turns the transistor off
Data Source
AI summary
A dynamic biasing circuit of the substrate of a MOS power transistor may include a first switch configured to connect the substrate to a current source which forward biases the intrinsic source-substrate diode of the transistor, when the gate voltage of the transistor turns the transistor on. The current source may include a stack of diodes in the same conduction direction as the intrinsic diode between the substrate and a supply voltage.