RFID AM Demodulation Using Dual Polarity Signal Extraction
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Solution Overview
Problem
Current AM demodulation systems for RFID reader devices are limited in effectively demodulating AM waves, especially when disturbed, due to their simplicity and non-linearity, which results in distorted outputs and difficulty in filtering digital signals, especially when the frequency of the square wave is close to the carrier wave frequency.
Innovation Solution
The implementation of a dual-demodulation system that captures both positive and negative amplitude sides of the AM wave, with each demodulator comprising a diode, capacitor, and resistor, and a subtractor block to produce an enforced demodulated output with a frequency twice that of the carrier wave, facilitating easier filtering of the digital signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple demodulator with few electronic components is used, then device complexity and cost are reduced, but measurement precision and reliability of demodulation deteriorate
Solution Approach 1:
The patent divides the demodulation function into multiple independent demodulators (first demodulator for positive amplitude side, second demodulator for negative amplitude side) instead of using a single complex demodulator. Each demodulator processes a specific portion of the AM wave, and their outputs are combined through subtraction to achieve accurate demodulation while keeping each individual demodulator simple.
2Device complexity
If a simple demodulator is used, then device complexity is reduced, but the ability to handle disturbed AM waves deteriorates
Solution Approach 1:
By segmenting the demodulation process into multiple parallel demodulators handling different amplitude sides, the system gains redundancy and robustness. If one demodulator experiences disturbances, the other can compensate, improving overall reliability while maintaining simplicity of individual components.
Solution Approach 2:
The patent implements a feedback mechanism where the outputs of multiple demodulators are subtracted to produce the final demodulated signal. This feedback loop allows the system to automatically compensate for disturbances and non-linearities, improving reliability without increasing the complexity of individual demodulator components.
3Productivity
If the frequency of the square wave is close to the carrier wave frequency, then data transmission efficiency is improved, but filtering difficulty increases
Solution Approach 1:
Instead of trying to filter out the carrier frequency from the demodulated signal, the patent inverts the approach by using frequency multiplication (through the subtraction of demodulated outputs) to shift the signal frequency to twice the carrier frequency. This creates a larger frequency gap that is easier to filter, solving the problem of close frequencies while maintaining transmission efficiency.
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 allows for a more precise and efficient extraction of the digital signal from the AM wave, reducing noise and distortion, and enabling easier filtering of the digital data, while maintaining a simple and cost-effective configuration.
Implementation Method 1
a simple and cheap demodulator includes a diode, a capacitor and a resistor
Implementation Method 2
a simple and cheap demodulator includes a diode, a capacitor and a resistor
Data Source
AI summary
An RFID reader device (31), of the type comprising a demodulator (6) for receiving from a RFID tag (11) an AM (Amplitude Modulation) wave (20) having a predetermined frequency (f) and for retrieving, from the AM wave (20), a demodulated output (6a) associated to predetermined positive or negative Amplitudes of said AM wave (20), said demodulated output having a portion with a frequency F. The AM demodulation system comprises at least a second demodulator (26) for receiving the AM wave (20) and retrieving a second demodulated output (26a) associated to Amplitudes opposite to the predetermined positive or negative Amplitudes, said second demodulated output having a portion with said frequency F; the RFID reader includes a block (27) having, in input, the demodulated output (6a) and the second demodulated output (26a) and returning, in output, an enforced demodulated output (30) with a portion with frequency (f1) doubled with respect to said frequency (F).