RFID Rectifier Circuit Biasing Weak AC Signals
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Solution Overview
Problem
Conventional rectifier circuits in RFID tags cannot rectify AC signals with a root-mean-square value less than the threshold voltage of approximately 0.7 V, limiting the communication distance and convenience, as well as the ability to detect multiple RFID tags simultaneously.
Innovation Solution
A rectifier circuit with a bias circuit that applies a constant voltage less than the threshold voltage between the gate and source of diode-connected MOS transistors, allowing for the rectification of AC signals with root-mean-square values below the threshold, and utilizing floating-gate transistors with predetermined potentials to enhance rectification capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional rectifier circuit with diode-connected MOS transistor is used, then the circuit structure is simple, but the AC signal with root-mean-square value less than the threshold voltage cannot be rectified
Solution Approach 1:
The invention applies a predetermined voltage (bias voltage) to the gate of the MOS transistor before the rectification process. This preliminary action shifts the transistor's operating point so that it can rectify AC signals with root-mean-square values below the original threshold voltage, while maintaining the simple diode-connected structure.
2Ease of operation
If the threshold voltage of the MOS transistor is used for rectification, then the circuit operation is straightforward, but the communication distance is limited to approximately 30 cm
Solution Approach 1:
The invention changes the voltage parameter applied to the MOS transistor gate from zero (conventional operation) to a predetermined bias voltage. This parameter change reduces the effective threshold voltage requirement, enabling the rectifier to process weaker AC signals from longer distances, thus expanding communication range beyond 30 cm.
3Device complexity
If a conventional rectifier circuit is used, then the circuit design is simple, but multiple RFID tags cannot be detected simultaneously
Solution Approach 1:
By applying a predetermined bias voltage to the MOS transistor gate before signal reception, the rectifier circuit becomes sensitive to weaker AC signals. This enables the simultaneous detection of multiple RFID tags at different power levels without increasing circuit complexity, as the bias voltage allows the circuit to process a broader range of input signal strengths.
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
Enables the rectification of weak AC signals, expanding the communication distance and allowing for simultaneous detection of multiple RFID tags, thereby improving the convenience and application range of RFID tags.
Implementation Method 1
a coupling capacitor that has a first end which is connected to the source of the first MOS transistor, and a second end to which an alternating-current signal is input
Implementation Method 2
A rectifier circuits converts alternating-current (AC) into direct-current (DC) through the rectification of diodes
Data Source
AI summary
A rectifier circuit includes a bias circuit that outputs a direct-current voltage; a first MOS transistor that has a gate and a source; and a second MOS transistor that has a gate, a source, and a drain connected to the source of the first MOS transistor. Only the direct-current voltage is applied between the gate and the source of the first MOS transistor, and only the direct-current voltage being applied between the gate and the source of the second MOS transistor. The rectifier circuit also includes a coupling capacitor that has a first end which is connected to the source of the first MOS transistor, and a second end to which an alternating-current signal is input.