Active Load Modulation Synchronization for Rapid NFC Card Sensing
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Solution Overview
Problem
Existing near field communication (NFC) technologies struggle to establish synchronization between a reader and an object in card-emulation mode when the reader senses the presence of a card rapidly, as the object does not have sufficient time to initialize its phase-locked loop within the short sensing period of the reader.
Innovation Solution
Implementing active load modulation (ALM) with a phase-locked loop (PLL) and frequency-locked loop (FLL) calibration methods to synchronize the oscillator frequency and phase of the object with the reader's field, allowing for rapid communication even when the sensing period is insufficient for full initialization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the reader uses rapid sensing to detect the object quickly, then the sensing time is reduced, but the object does not have sufficient time to initialize its phase-locked loop
Solution Approach 1:
The oscillator frequency is pre-calibrated to match the reader's sensing frequency before the actual sensing process begins. This preliminary calibration ensures that when the reader rapidly senses the object, the phase-locked loop is already prepared and can synchronize immediately without requiring the full initialization time, thus resolving the contradiction between rapid sensing and sufficient initialization time.
2Measurement precision
If the phase-locked loop is fully initialized, then synchronization accuracy is improved, but the initialization time exceeds the reader's sensing period
Solution Approach 1:
Instead of performing the complete phase-locked loop initialization sequence, the invention applies only the necessary partial initialization - specifically calibrating the oscillator frequency to match the reader's sensing frequency. This partial action is sufficient to achieve the required synchronization accuracy for rapid sensing operations, avoiding the time penalty of full initialization while maintaining adequate precision.
3Loss of time
If the oscillator frequency is calibrated using an internal clock, then the calibration time is reduced, but frequency accuracy may be compromised
Solution Approach 1:
The object uses its own internal clock to generate the calibration signal for the oscillator, rather than relying on an external reference from the reader. This self-service approach allows the object to perform frequency calibration independently and rapidly using its existing internal timing resources, significantly reducing calibration time while achieving sufficient frequency accuracy for the application.
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
Enables communication with rapid sensing readers by calibrating the oscillator frequency and phase within a short time frame, ensuring synchronization and enabling effective data exchange between the reader and object.
Implementation Method 1
The reader is then configured to generate a magnetic field through its antenna
Implementation Method 2
A phase-locked loop of object is initialized... the phase-locked loop is implemented to adjust the phase of the oscillator
Implementation Method 3
contactless communication method between an object and a reader using active load modulation
Data Source
AI summary
In one embodiment, an object can communicate contactlessly with a reader using active load modulation. The method includes detecting a sensing magnetic field emitted by the reader, initializing a phase-locked loop of the object, detecting a stopping of the sensing magnetic field emitted by the reader before initializing the phase-locked loop of the object is complete, calibrating an oscillator of the phase-locked loop on the basis of an internal clock of the object, detecting a new sensing magnetic field of the reader after calibrating the oscillator, and implementing the phase-locked loop to adjust the phase of the oscillator after detecting a new sensing magnetic field.