Active Load Modulation Clock Sync for NFC Phase Stability
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Solution Overview
Problem
Active load modulation in NFC communication can result in phase shifts between the signal emitted by a reader and the signal received from an object, particularly during long transmission periods, leading to non-synchronous responses and reduced communication efficiency.
Innovation Solution
A method involving a calibration phase to lock the main oscillator's frequency and phase with the reader's secondary clock signal, followed by a transmission phase where the main clock signal is frequency-locked to a reference signal, minimizing or eliminating phase shifts through the use of phase-locked and frequency-locked loops, and adaptive filters to maintain synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If active load modulation is used for NFC communication, then communication distance and power autonomy are improved, but phase shifts occur between reader and object signals during long transmission periods
Solution Approach 1:
The patent applies preliminary action by performing a calibration phase before actual data transmission. During this calibration phase, the object adjusts its oscillator frequency and phase based on the reader's clock signal to predict and eliminate future phase shifts. This preparatory synchronization ensures that when long-distance active load modulation communication begins, the phase relationship is already optimized, preventing the synchronization problems that would otherwise occur during extended transmission periods.
Solution Approach 2:
The patent implements feedback by continuously monitoring the phase difference between the reader's clock signal and the object's transmitted signal. The object uses this feedback information to dynamically adjust its oscillator parameters, creating a closed-loop control system. This feedback mechanism allows the object to compensate for drift and maintain synchronization even during long transmission periods, resolving the reliability issue while preserving the extended communication distance capability.
2Use of energy by moving object
If the object generates its own electromagnetic field with independent oscillator, then power autonomy and communication distance are improved, but frequency drift and phase shifts occur
Solution Approach 1:
The patent uses the reader's clock signal as an intermediary reference. Instead of relying solely on the object's independent oscillator which may drift, the object periodically references the reader's clock signal during calibration and uses it as a stable frequency standard. This intermediary reference allows the object to maintain its power autonomy while achieving frequency synchronization, as the reader's clock serves as a common time base that both devices can reference.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the object's oscillator frequency and phase parameters based on calibration measurements. The object modifies its operating parameters to match the reader's expected frequency, compensating for the inherent drift of independent oscillators. This parameter adjustment allows the system to maintain frequency synchronization precision while preserving the power autonomy benefits of having an independent object oscillator.
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 significantly reduces or eliminates phase shifts, ensuring synchronous communication and maintaining the desired frequency, thereby enhancing the reliability and efficiency of NFC transactions over longer distances.
Implementation Method 1
generation of a main clock signal within said object... frequency of said main clock signal is substantially equal to the frequency of said secondary clock signal
Implementation Method 2
controlling an output signal of a main oscillator on a frequency and a phase of a secondary clock signal received from the reader
Implementation Method 3
frequency-only slaving of an output signal of the main oscillator on a frequency of the reference signal
Implementation Method 4
an estimation of a frequency ratio between an output frequency of the main oscillator and a reference frequency of a reference signal
Data Source
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AI summary
A method for contactless communication of an object with a reader by active charge modulation, comprising a first communication mode including the generation of a main clock signal (SH1) within said object including a calibration phase comprising the control of the output signal (SSP) of a controlled main oscillator (OSCP) to the phase and frequency of a secondary clock signal (SH2) received from the reader (RD) and an estimation of a frequency ratio between the frequency of the output signal (SSP) of the main oscillator and a reference frequency of a reference signal (SRF) from a reference oscillator (OSCR) and a transmission phase comprising frequency control only of the output signal (SSP) of the main oscillator to the frequency of the reference signal corrected by said estimated ratio, said main clock signal (SH1) being derived from the output signal (SSP) of the main oscillator.