Hybrid RF Rectifier for Passive RFID Tags
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Solution Overview
Problem
Passive RFID tags face challenges in efficiently converting low-level RF signals into usable voltage due to insufficient RF signal amplitude and intermittent energy harvesting, which affects their operation and memory programming.
Innovation Solution
The implementation of a hybrid RF rectifier stage using Schottky diodes and MOS transistors, along with dual antenna configurations, to maximize energy harvesting and provide stable voltage for RFID tag operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If charge-pump circuits are used to increase output DC voltage from low-level RF signals, then the voltage can reach typical supply voltage levels (1V), but the circuit complexity increases and energy efficiency decreases
Solution Approach 1:
The patent changes the operating parameters of the rectifier by using bipolar transistors configured to operate in different regions (active region for amplification, saturation region for switching) depending on the input signal level. This allows the circuit to achieve high voltage gain without requiring complex multi-stage charge-pump architectures, thereby reducing overall circuit complexity while maintaining the ability to generate sufficient DC voltage from low-level RF signals.
2Power
If conventional rectifier circuits are used, then voltage can be generated from RF signals, but the conversion efficiency is insufficient when RF signal amplitude is only approximately 200 mV
Solution Approach 1:
The patent implements a dynamic rectifier circuit where bipolar transistors switch between different operating states based on the instantaneous RF signal level. The circuit dynamically adjusts its gain and impedance characteristics to maximize energy harvesting from weak RF signals (200 mV range). This dynamic operation allows efficient conversion of low-amplitude RF signals to usable DC voltage, overcoming the inefficiency of static conventional rectifier designs.
3Loss of information
If the RFID tag backscatters RF waves to transmit data, then communication is achieved, but energy harvesting is interrupted causing voltage generation to cease
Solution Approach 1:
The patent incorporates energy storage capacitors that are charged during periods when the RFID tag is not backscattering. These capacitors store sufficient energy to maintain voltage generation during brief backscatter intervals when data transmission occurs. This preliminary energy accumulation allows the circuit to bridge the gaps in energy harvesting caused by intermittent backscatter operations, ensuring continuous power supply for tag operations.
4Power
If higher voltage (up to 12V) is needed for memory programming and erasing, then boosted voltage can be generated, but the rectifier circuit becomes more complex and less efficient
Solution Approach 1:
The patent merges the voltage boosting function with the existing rectifier circuit by using the same bipolar transistor stages for both rectification and voltage multiplication. The circuit leverages the natural gain characteristics of bipolar transistors to achieve the required 12V boost for memory operations without adding separate voltage multiplication stages. This integrated approach maintains efficiency while providing the necessary high voltage for programming and erasing operations.
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 solution enhances the efficiency of energy conversion from RF signals to usable voltage, ensuring reliable operation and memory functionality in passive RFID tags, even with intermittent RF signal availability.
Implementation Method 1
hybrid RF rectifier stage using Schottky diodes and MOS transistors to maximize energy harvesting and provide stable voltage
Implementation Method 2
MOS transistors configured in a common-source amplifier arrangement to provide voltage amplification
Implementation Method 3
bipolar transistor arranged in a common-emitter configuration to provide additional voltage amplification
Data Source
AI summary
The present disclosure provides a power rectifier for a Radio Frequency Identification tag circuit. The power rectifier is constructed from a pair of hybrid RF rectifier elements that include a MOS transistor. Gates of the transistors have predetermined voltages applied to them. The applied voltages bias the transistors to near their active operating regions, while an additional RF control signal is being applied to the gates of the transistors.