RFID Interrogator Chopper Sampling for Signal Isolation
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Solution Overview
Problem
RFID systems face challenges in receiving low-amplitude, low-frequency backscattered signals due to high carrier signal attenuation, leading to poor signal-to-noise ratios and interference from 'blackholes' in the activation field, where backscattered signals are not correctly received, and existing Interrogators struggle with multiple frequency communications.
Innovation Solution
An enhanced RFID Tag Interrogator apparatus featuring a current transformer, antenna, zero cross detector, phase shifter, pulse generator, chopper, and bandpass filter, along with a Variable Bandpass Multi-Band Demodulator, which samples and filters backscattered signals to improve signal-to-noise ratio and enable simultaneous communication with multiple RFID Tags operating on different frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the transmission power is increased to raise the level of backscattered signals, then the signal amplitude improves, but the transmission power limitations are exceeded and the signal to noise ratio does not improve
Solution Approach 1:
A chopper is introduced as an intermediary device that samples the backscattered signal at its zero-crossing points. This mediator extracts the modulation information from the backscattered signal without requiring amplification of the entire signal, thereby improving signal retrieval without increasing transmission power
Solution Approach 2:
The system performs preliminary detection of zero-crossing points in the backscattered signal before full signal processing. By identifying these critical timing points in advance, the system can accurately sample the modulation information without needing to amplify the weak backscattered signal, thus avoiding power limitations
2Reliability
If conventional reception methods are used, then the system structure remains simple, but blackholes appear in the activation field where backscattered signals cannot be correctly received
Solution Approach 1:
A chopper serves as an intermediary sampling device that extracts modulation information at zero-crossing points. This intermediary approach enables reliable signal reception in previously problematic blackhole regions without requiring complex array structures
Solution Approach 2:
The system performs preliminary detection of zero-crossing points before full signal processing. This preliminary timing information allows accurate sampling of backscattered signals even in regions where conventional methods fail, improving reception reliability without excessive complexity
3Productivity
If the carrier signal amplitude is high, then the transmission efficiency is good, but the backscattered signals are attenuated and difficult to isolate
Solution Approach 1:
The system performs preliminary detection of zero-crossing points in the combined carrier and backscattered signal. By identifying these timing points in advance, the system can accurately sample the backscattered modulation information without needing to attenuate the carrier signal, thus maintaining transmission efficiency while improving detection precision
Solution Approach 2:
The chopper acts as an intermediary that samples the signal at zero-crossing points, effectively separating the backscattered modulation information from the strong carrier signal. This timing-based separation allows high carrier amplitudes to be maintained for efficient transmission while still enabling precise backscattered signal detection
4Measurement precision
If a single antenna system is used, then the device complexity is low, but signals interfere with each other and backscattered signal isolation is difficult
Solution Approach 1:
The system performs preliminary detection of zero-crossing points in the received signal. This timing information allows accurate sampling of backscattered signals even in single-antenna systems where transmitted and received signals originate from the same point, improving isolation without requiring multiple antennas
Solution Approach 2:
The chopper serves as an intermediary sampling device that extracts backscattered signal information at zero-crossing points. This timing-based extraction method effectively isolates backscattered signals from transmitted signals in single-antenna configurations without requiring complex antenna arrays
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 significantly enhances the signal-to-noise ratio for backscattered signal reception, eliminates 'blackholes' in the activation field, and allows for simultaneous communication with multiple RFID Tags operating on various frequencies, improving data retrieval accuracy and reducing transmission power requirements.
Implementation Method 1
having a current transformer and an antenna
Implementation Method 2
a zero cross detector for receiving an input current waveform from the current transformer and for producing a sampling signal based on the input current waveform
Implementation Method 3
a phase shifter for phase shifting the sampling signal by about ninety degrees to produce a phase shifted sampling signal
Implementation Method 4
the chopper for receiving and sampling a backscattered carrier signal from the antenna
Implementation Method 5
a bandpass filter for filtering away a carrier signal of the backscattered carrier signal
Implementation Method 6
The Interrogator communicates with the RFID Tags by transmitting carrier signals modulated with data to the RFID Tags. The RFID Tags in turn modulates the modulated carrier signals from the Interrogator using modulated backscattering and reflects and replies to the Interrogator
Data Source
AI summary
An apparatus for an enhanced receiver for an RFID Tag Interrogator is described. The enhanced receiver has a zero crossing detector, a phase shifter, a pulse generator and a chopper. The zero crossing detector produces a sampling signal from the current transformer. The phase shifter modifies the sampling signal by producing a 90 degree phase shifted sampling signal. The pulse generator increases time duration of each pulse of the phase shifted sampling signal, which is then fed to the chopper. Thus, the chopper samples the backscattered carrier signal every 90 degree phase shift from the time when the backscattered carrier signal passes the zero crossing. This makes isolation of the backscattered signal from the carrier signal more effective.