Passive RFID Reader Signal Shifting for Weak Chip Detection
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Solution Overview
Problem
Current methods for processing signals from passive RFID chips, particularly in low-frequency (LF) RFID contactless cards, face challenges in amplifying weak signals effectively without incurring significant costs, and existing solutions are limited to specific types of signal modulation and do not utilize operational amplifiers for signal shifting.
Innovation Solution
A method employing an operational amplifier connected as a summing amplifier, in conjunction with an antenna, analog-to-digital (AD) converter, and digital-to-analog (DA) converters, to process both positive and negative half periods of the signal, using calibrated voltage ratios to shift the signal for enhanced processing by the AD converter, thereby amplifying weak signals without additional external components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional external components are used to amplify the signal, then the signal strength is improved, but the cost and device complexity increase considerably
Solution Approach 1:
The operational amplifier is configured as a summing amplifier that performs multiple functions: it amplifies the weak RFID signal, shifts the signal level to match the ADC input range, and processes both positive and negative half-periods of the signal. This multi-functionality eliminates the need for separate amplification and level-shifting components, reducing overall device complexity while maintaining signal strength improvement
Solution Approach 2:
The patent changes the operational parameters of the summing amplifier by adjusting the ratio of feedback resistor Rf to input resistor Ri (gain factor) and by controlling the DC voltage applied to the non-inverting input. This allows the same circuit to adapt to different signal conditions and modulation types (ASK, FSK, PSK) without requiring additional components, thereby improving signal strength while keeping device complexity low
2Measurement precision
If existing signal processing methods are used, then the processing is simpler, but the reading quality and sensitivity to weak signals deteriorate
Solution Approach 1:
The patent implements dynamic signal processing by using a summing amplifier configuration that can adaptively process both positive and negative half-periods of the signal. The circuit dynamically adjusts the signal level through the gain factor (Rf/Ri) and the DC voltage at the non-inverting input, enabling high reading quality for weak signals while maintaining a relatively simple circuit structure compared to static amplification methods
3Reliability
If the signal is processed without shifting, then the device complexity is reduced, but the AD converter cannot properly process signals outside its input range
Solution Approach 1:
The patent merges the signal amplification function and the signal level-shifting function into a single summing amplifier circuit. The amplifier simultaneously scales the input signal by the gain factor (Rf/Ri) and adds a DC offset voltage from the non-inverting input, ensuring the output signal falls within the ADC input range. This combination eliminates the need for separate amplification and level-shifting stages, achieving reliable signal processing while keeping device complexity low
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 increases the sensitivity of the RFID reader to process weak signals across various modulation types (ASK, FSK, and PSK), improving reading quality without additional costly components, and is applicable for contactless authorization systems like printers and photocopiers.
Implementation Method 1
the received RFID chip signal and the output of the first DA converter is fed to the inverting input of the operational amplifier, and the output of the second DA converter or the output of the source of constant voltage is fed to the non-inverting input of the operational amplifier
Data Source
AI summary
The subject of the invention Is a method of processing a signal of a passive RFID chip (1) with a reader (2) in order to amplify the useful signal. A method of processing a signal of a passive RFID chip (1) with a reader (2) comprising an antenna (3), an operational amplifier (4), an AD converter (5) and a first DA converter (6) and a second DA converter (7) or a source of constant voltage consists of steps of transmitting the source signal of the antenna (3), receiving the source signal of the antenna (3) by the RFID chip (1), transmitting the RFID chip (1) signal and receiving the RFID chip (1) signal by the antenna (3), wherein the received RFID chip (1) signal and the output of the first DA converter (6) is fed to the inverting input of the operational amplifier (4) and the output of the second DA converter (7) or the output of the source of constant voltage is fed to the non-inverting input of the operational amplifier (4). After converting the signal by the AD converter (5) the amplitude of two consecutive peaks belonging to a single wave is subtracted, wherein the individual signals are temporarily stored in the buffer (12) before subtraction.