RF-DC Rectifier With Hybrid Threshold Compensation
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Solution Overview
Problem
RF energy harvesting systems face challenges in efficiently converting weak RF signals into DC power due to limited signal strength and low efficiency of the harvesting circuit, particularly at low input power levels, primarily due to high threshold voltages of rectifying devices, which increase power consumption and reduce output voltage.
Innovation Solution
A hybrid forward and backward threshold voltage compensation scheme is implemented using PMOS transistors as rectifying devices in most stages, with compensating voltage provided by connecting the gate terminal to previous or later stages, and an adaptive method to control the ON/OFF operation of MOS transistors, reducing the need for triple-well NMOS transistors and minimizing reverse leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If standard rectifying devices are used in RF-DC power conversion circuit, then the circuit structure is simple, but the threshold voltage is high which reduces power conversion efficiency and output voltage at low input power levels
Solution Approach 1:
The rectifier is divided into multiple stages with different rectifying devices. The first stage uses a standard rectifying device (diode or transistor) while subsequent stages use transistors with dynamically controlled threshold voltages. This segmentation allows the circuit to maintain simplicity in the first stage while achieving high efficiency in later stages through active threshold control.
Solution Approach 2:
The threshold voltage of transistors in the rectifier stages is dynamically controlled by adjusting their gate-source voltages. By varying the gate voltage, the threshold voltage is modulated to optimize rectification efficiency at different operating conditions. This dynamic control enables the rectifier to adapt to low input power levels while maintaining high conversion efficiency.
2Loss of energy
If the threshold voltage of rectifying devices is reduced to improve efficiency, then power conversion efficiency increases, but reverse leakage current increases which reduces overall performance
Solution Approach 1:
The gate-source voltage of each transistor is dynamically adjusted during operation. During the rectification phase, the gate voltage is set to provide a low threshold voltage for efficient current flow. During the reverse bias phase, the gate voltage is modified to increase the threshold voltage and minimize reverse leakage current. This dynamic voltage control resolves the trade-off between forward conduction efficiency and reverse leakage suppression.
Solution Approach 2:
The rectifying devices operate in periodic cycles, alternating between forward conduction mode and reverse blocking mode. During forward conduction, threshold voltage is reduced for efficient current flow. During reverse blocking, threshold voltage is increased to minimize leakage. This periodic switching of operating modes enables the system to achieve both high efficiency and low leakage over complete operation cycles.
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 power conversion efficiency and reduces the power-up threshold, allowing operation at lower input power levels while maintaining high output voltage, effectively addressing the trade-off between threshold voltage reduction and leakage current, and is suitable for fully battery-less applications.
Implementation Method 1
The power harvester unit 20 comprising a multi-stage rectifier 26 is a key component in RF energy harvesting systems. It converts the incoming weak RF signal into a DC voltage.
Data Source
AI summary
A rectifier comprising a chain of transistors for RF-DC conversion. In order to compensate for the thresholds of the transistors, each transistor can be connected to a junction earlier or later in the chain. By using both p-type and n-type transistors in the same chain, the different types of transistors can be compensated in different directions allowing more transistors to be compensated. Additional transistors connected to the gates of transistors of the main chain can allow the transistors of the main chain to be forward compensated at one part of the input cycle and backward compensated in another part to minimize both the voltage threshold of the rectifier and the leakage current. The line for compensation of the voltage threshold during forward conduction can comprise a solid line or a transistor, and if a transistor is used it may be diode-connected.