Variable-Capacitance Diode Protection for Passive RFID Chips
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Solution Overview
Problem
Passive RFID chips are vulnerable to damage from high-intensity electromagnetic fields, which can cause excessive DC voltage, potentially harming the logic circuit and input/output circuit when attempting to retrieve identifying information at longer distances with higher energy electromagnetic waves.
Innovation Solution
Incorporation of a variable-capacitance diode with a threshold voltage greater than the safe operational voltage and a diode forming a feedback path to reduce the antenna's quality factor, thereby limiting the output voltage and preventing damage from high-intensity electromagnetic waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If high-energy electromagnetic waves are used to retrieve identifying information at longer distances, then the reading distance is improved, but the DC voltage output increases and may damage the logic circuit
Solution Approach 1:
The patent introduces a variable-capacitance diode connected between the antenna output and ground, and a feedback diode connected between the power unit output and antenna output. These diodes are positioned in advance to cushion against voltage spikes before they can damage the logic circuit. When high-energy electromagnetic waves cause excessive voltage, the variable-capacitance diode conducts to ground, and the feedback diode creates a feedback path that reduces the antenna's quality factor, thereby limiting the voltage increase before it reaches harmful levels.
Solution Approach 2:
The patent implements a feedback mechanism using a feedback diode connected between the power unit output and the antenna output. When the DC voltage from the power unit exceeds a certain threshold, this diode conducts and creates a feedback path that reduces the antenna's quality factor (Q-value). This feedback action automatically limits the voltage gain from high-energy electromagnetic waves, preventing excessive DC voltage from damaging the logic circuit while maintaining normal operation at lower energy levels.
2Reliability
If the antenna's quality factor is reduced to limit output voltage, then the protection against high-intensity electromagnetic waves is improved, but the power transfer efficiency decreases
Solution Approach 1:
The patent employs a variable-capacitance diode whose capacitance value changes dynamically based on the voltage level. At normal operating voltages, the diode remains non-conducting or operates in a high-impedance state, maintaining the antenna's high quality factor and efficient power transfer. When high-intensity electromagnetic waves cause voltage to exceed the diode's threshold, it switches to a conducting state, dynamically reducing the antenna's quality factor to limit further voltage increase. This dynamic behavior allows the system to maintain high efficiency during normal operation while providing protection during abnormal high-energy conditions.
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 effectively protects the logic and input/output circuits by reducing the amplitude of AC signals and output voltage when exposed to high-intensity electromagnetic waves, ensuring safe operation within predetermined voltage limits.
Implementation Method 1
a variable-capacitance diode including an anode connected with the output of the antenna and a cathode connected to ground
Implementation Method 2
The power unit 200 includes two diodes and two capacitors that are connected in a form for rectifying and smoothing the electrical signals sent by the antenna 100 and outputting a stable DC (direct current) voltage VDD
Implementation Method 3
a diode including an anode connected with the output of the power unit and a cathode connected with the output of the antenna
Data Source
AI summary
A passive radio frequency identification (RFID) chip with a protection function against high-intensity electromagnetic fields includes an antenna for receiving electromagnetic waves generated by an RFID reader and generating AC electrical signals to output to a power unit at an output of the antenna; an input/output circuit; a logic circuit; the power unit for rectifying the AC electrical signals into DC (direct current) voltage and outputting the DC voltage to the logic circuit and the input/output circuit at an output of the power unit; a variable-capacitance diode including an anode connected with the output of the antenna and a cathode connected to ground; and a diode including an anode connected with the output of the power unit and a cathode connected with the output of the antenna. The passive RFID chip prevents the inner logic circuit and the input/output circuit from being damaged when receives high-intensity electromagnetic waves.