Wireless Sensor Reader Using Phase-Locked Loop for Low Power
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Solution Overview
Problem
Current passive wireless sensor readers face issues such as large size, high power consumption, inaccuracy, and interference due to wide bandwidth requirements, which limit their use and longevity, especially in battery-powered devices.
Innovation Solution
A reader device that transmits a short pulse of energy at a fixed frequency to excite the sensor, allowing it to ring at its resonant frequency, and uses a phase-locked loop to lock onto and measure the sensor's ring signal, reducing power consumption and complexity while minimizing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frequency sweeps and wide bandwidth transmission are used to excite the sensor, then the sensor can be reliably excited across varying resonant frequencies, but the reader device consumes high power and creates electromagnetic interference
Solution Approach 1:
The patent implements periodic frequency sweeps at controlled intervals rather than continuous wide bandwidth transmission. The reader performs frequency sweeps only when needed to track sensor resonant frequency changes, allowing the system to maintain reliability while reducing overall power consumption by keeping the transmitter in a low-power state between sweeps.
Solution Approach 2:
The patent dynamically adjusts transmission parameters including frequency, bandwidth, and power level based on detected sensor resonant frequency. The reader starts with wide bandwidth frequency sweeps to locate the sensor, then transitions to narrowband transmission at the detected resonant frequency, significantly reducing power consumption and electromagnetic interference while maintaining reliable excitation.
2Measurement precision
If wide bandwidth frequency sweeps are transmitted to locate sensor resonant frequency, then the sensor can be reliably detected, but electromagnetic interference increases and regulatory compliance becomes difficult
Solution Approach 1:
The patent performs frequency sweeps periodically rather than continuously, limiting electromagnetic interference to specific time windows. Between sweeps, the reader operates in receive mode or remains in low-power state, reducing overall interference while maintaining the ability to accurately detect sensor resonant frequency when sweeps are performed.
Solution Approach 2:
The patent dynamically changes transmission frequency and bandwidth parameters. It starts with wide bandwidth sweeps at low power to locate the sensor resonant frequency, then transitions to narrowband operation at the detected frequency with optimized power levels, thereby maintaining detection accuracy while minimizing electromagnetic interference during normal operation.
3Measurement precision
If continuous transmission is used to maintain PLL lock on sensor frequency, then frequency tracking accuracy is improved, but power consumption increases
Solution Approach 1:
The patent implements periodic PLL locking rather than continuous locking. The reader performs frequency sweeps to update the PLL lock frequency, then maintains lock between sweeps. This periodic approach allows the system to retain frequency tracking accuracy while significantly reducing power consumption by keeping the PLL and transmitter in low-power states between updates.
Solution Approach 2:
The patent allows the sensor to serve as the frequency reference for the PLL, eliminating the need for a high-precision internal crystal oscillator in the reader. The PLL locks to the sensor's resonant frequency itself, which the sensor maintains passively, thereby reducing the reader's power consumption while maintaining accurate frequency tracking.
4Reliability
If multiple energizing loops with different frequencies are used, then complete sensor excitation is achieved, but device complexity and size increase
Solution Approach 1:
The patent implements a dynamic frequency selection approach where the reader determines the sensor's resonant frequency through frequency sweeps and then configures a single energizing loop to operate at that frequency. This dynamic adaptation replaces the need for multiple fixed-frequency loops, achieving complete sensor excitation while significantly reducing device complexity and size.
Solution Approach 2:
The patent changes the operating frequency parameter of the energizing loop based on detected sensor characteristics. Rather than using multiple loops with fixed frequencies, the system adjusts the frequency of a single loop to match the sensor's resonant frequency, achieving effective excitation with simpler circuitry.
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 enables a compact, low-power, and accurate measurement system that complies with electromagnetic regulations, suitable for battery operation and frequent use in biomedical applications.
Implementation Method 1
transmits a pulse of energy at a fixed frequency to cause the sensor to ring at its resonant frequency
Implementation Method 2
the sensor's resonant frequency varies proportionately with the sensed parameter value... cause the sensor to ring at its resonant frequency
Implementation Method 3
uses a phase-locked loop to lock onto and measure the sensor's ring signal
Data Source
AI summary
A wireless sensor reader is provided to interface with a wireless sensor. The wireless sensor reader transmits a narrowband, fixed frequency excitation pulse to cause the wireless sensor to generate a ring signal. The ring signal corresponds to the value of the physical parameter being sensed. The wireless sensor reader receives and amplifies the ring signal and sends the signal to a phase-locked loop. A voltage-controlled oscillator in the phase-locked loop locks onto the ring signal frequency and generates a count signal at a frequency related to the ring signal frequency. The voltage-controlled oscillator is placed into a hold mode where the control voltage is maintained constant to allow the count signal frequency to be determined. The low power, simple circuitry required to generate the excitation pulse allows the reader to be a small, battery operated unit. Alternative methods of frequency determination are also disclosed.