Active Load Modulation PLL Calibration for Fast NFC Polling
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Solution Overview
Problem
Some NFC readers quickly probe for cards, emitting a magnetic field for a short duration, which is insufficient for objects in card mode to initialize their phase-locked loop, preventing communication even if the object is present.
Innovation Solution
The method involves detecting a reader's probing magnetic field, initializing and calibrating the phase-locked loop using an internal clock, and adjusting the oscillator phase to respond quickly to the reader's field, allowing communication even if the initialization time exceeds the reader's probing period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the reader emits a magnetic field for a short duration to quickly probe for cards, then the probing speed is improved, but the object does not have enough time to initialize its phase-locked loop, preventing communication
Solution Approach 1:
The object performs preliminary calibration of its oscillator using an internal reference clock before the reader's probing field is emitted. This preliminary action allows the phase-locked loop to be pre-configured with accurate frequency and phase information, so that when the reader's field arrives, the object can immediately lock onto it without requiring a lengthy initialization period. This resolves the contradiction by preparing the system in advance, enabling fast probing while maintaining proper synchronization.
Solution Approach 2:
The object uses its own internal reference clock to calibrate its oscillator, rather than relying on the reader's field for initial frequency establishment. This self-service approach allows the object to independently prepare its phase-locked loop with accurate timing information before the reader's probing field is emitted, enabling the object to quickly respond to fast-probing readers without compromising synchronization accuracy.
2Measurement precision
If the object waits for complete phase-locked loop initialization before responding, then synchronization accuracy is improved, but the response time becomes too slow for fast-probing readers
Solution Approach 1:
The object performs preliminary calibration of its oscillator using an internal reference clock before the reader's probing field is emitted. This preliminary action allows the phase-locked loop to be pre-configured with accurate frequency and phase information, so that when the reader's field arrives, the object can immediately lock onto it without requiring a lengthy initialization period. This resolves the contradiction by preparing the system in advance, enabling fast probing while maintaining proper synchronization.
Solution Approach 2:
The object changes the operational parameters of its phase-locked loop by switching from a cold-start initialization mode to a pre-calibrated mode. By pre-calibrating the oscillator frequency and phase using the internal reference clock, the system can rapidly acquire the reader's field with high synchronization accuracy, transforming the slow initialization process into a fast response capability while maintaining measurement precision.
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 objects to communicate with fast-probing NFC readers by calibrating the phase-locked loop frequency and phase within the reader's polling period, ensuring timely response and initiating communication.
Implementation Method 1
The reader is then configured to generate a magnetic field via its antenna
Implementation Method 2
the object is configured to modulate a beatless field amplitude
Data Source
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AI summary
According to one aspect, an object is proposed that is configured to perform contactless communication with a reader (RD) using active load modulation, the object comprising: - means for detecting (ANTC) a field of a reader, - a phase-locked loop (PLL) comprising an oscillator (DCO) and being configured to lock a phase of the oscillator (DCO) to the field of the reader (RD), - a calibration system (SYSC) for the frequency of the oscillator (DCO) of the phase-locked loop configured to calibrate the frequency of the oscillator (DCO) from an internal clock (CLKXO) when said detection means detect a stoppage of the field of the reader before the end of an initialization of said phase-locked loop of said object, and then to adjust the phase of the oscillator (DCO) when a new field of the reader (RD) is detected.