RF Voltage Limiting for NFC Devices Using Analog and Digital Control
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Solution Overview
Problem
Conventional RF limiters for NFC devices face challenges in maintaining signal integrity and protecting the device from damage due to slow response during fast field strength changes, and they lack protection during power-off mode.
Innovation Solution
A device comprising an analog limiter, sensing circuit, and digital controller that limits RF input voltage to a safe range during power-off or power-up, with the digital controller taking over the RF limiting function after power-on to prevent distortion and ensure device protection, using an on-chip rectifier for power-off mode protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a large on-chip capacitor is used in the conventional analog limiter to achieve slow response, then the distortion to ASK modulation is reduced, but the reliability of the NFC device is compromised due to slow response and extended settlement time
Solution Approach 1:
The patent divides the RF limiting function into two separate components: an analog limiter for fast response during power-off mode and a digital limiter for precise control during power-on mode. This segmentation allows each component to be optimized for its specific function, resolving the contradiction between fast response and signal integrity.
Solution Approach 2:
The patent implements dynamic switching between analog and digital limiting modes based on the power state. During power-off, the analog limiter provides fast response; during power-on, the digital limiter takes over for precise control. This dynamic approach allows the system to adapt its response characteristics to different operational requirements.
2Reliability
If the conventional analog limiter operates during power-off mode, then device protection is provided, but the response is too slow to protect against fast field strength changes
Solution Approach 1:
The patent prepares both analog and digital limiting circuits in advance, with the analog limiter already active during power-off mode for immediate protection. When power is applied, the digital limiter is quickly activated to take over, ensuring no protection gap exists. This preliminary preparation of multiple limiting mechanisms resolves the speed-reliability contradiction.
3Reliability
If the RF limiter uses a very short time constant for fast response, then device protection is improved, but the ASK modulated signal becomes distorted
Solution Approach 1:
The patent introduces a control circuit as an intermediary that manages the switching between analog and digital limiting modes. This intermediary coordinates the operation of both limiters, ensuring that the fast-response analog limiter operates only when necessary (during power-off), while the digital limiter handles normal operation to preserve signal integrity. This mediation resolves the contradiction between protection speed and signal quality.
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 effectively protects NFC devices during both power-on and power-off modes while maintaining signal integrity by using a fast-response analog limiter and a digital limiter that operates without causing distortion to ASK modulated signals, ensuring reliable communication.
Implementation Method 1
using an on-chip rectifier for power-off mode protection
Data Source
AI summary
The embodiments of the invention provide a method and device for radio frequency (RF) limiting. The device for RF limiting comprises: an analog limiter configured to limit a voltage of a RF input to a predetermined safe range during power-off or power-up until a disable control signal is received from the digital controller, a sensing circuit configured to sense a plurality of shunting currents provided by the analog limiter in sequence to determine a value of each bit of a preset current sensing code and sense the limiting voltage, a digital controller configured to control the digital limiter to perform RF limiting function based on the value of each bit of the preset current sensing code, and control the analog limiter to stop limiting the voltage of the RF input if the limiting voltage is within a predetermined acceptable voltage range.