NFC IC Current Control for Stable UICC Power Switching
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Solution Overview
Problem
In mobile communications devices, switching on the NFC chip to supply power to the UICC during an off state can cause a current peak, leading to a voltage drop on the power supply rail, potentially resetting the NFC integrated circuit or causing functionality issues.
Innovation Solution
A current control circuit is implemented, using a series of transistors and switches to manage the switching on of the power supply to the UICC, preventing voltage drops by controlling current flow through the power supply rail, ensuring stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple switch is used to supply power to UICC from internal regulator, then current consumption is reduced and device simplicity is improved, but voltage stability deteriorates due to current peaks when switching on
Solution Approach 1:
The power supply circuit is segmented into multiple functional blocks: a simple switch for power routing, a current control circuit with current source for regulated current delivery, and a transistor-based current regulation stage. This segmentation allows each block to perform its specific function optimally while maintaining overall system simplicity and voltage stability.
Solution Approach 2:
The current control circuit implements feedback control by monitoring the current flow through the switch and adjusting the current source output accordingly. This feedback mechanism prevents current peaks during switch-on by dynamically regulating the current to match the load requirements, thereby maintaining voltage stability on the power supply rail.
2Adaptability or versatility
If a low ohmic switch is used to provide compliant supply (1.62V @ 10ma), then ETSI standard compliance is improved, but voltage drop increases when switching on due to external capacitance loading
Solution Approach 1:
The current control circuit acts as an intermediary between the low ohmic switch and the UICC load. It buffers the switch from the capacitive loading effects by providing controlled current delivery, preventing direct voltage stress on the power supply rail while maintaining the low voltage drop characteristics required for ETSI compliance.
Solution Approach 2:
The circuit dynamically changes the current delivery parameter during switching transitions. The current control circuit adjusts the current magnitude and timing to account for the external capacitance on the UICC supply, ensuring that voltage remains within ETSI specifications (1.62V @ 10ma) without experiencing harmful voltage drops during switch-on.
Data Source
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AI summary
A near field communications (NFC) integrated circuit and method for a mobile communications device. The integrated circuit includes a power supply rail for providing a regulated supply of power to components within the integrated circuit. The integrated circuit also includes a first transistor coupled between the power supply rail and a power supply output of the integrated circuit for selectively providing power to a universal integrated circuit card (UICC) of the mobile communications device from the power supply rail while the mobile communications device is in an off state. The integrated circuit further includes a current control circuit for controlling the operation of the first transistor to prevent a drop in voltage on the power supply rail as the first transistor is switched to an on state to couple the power supply rail to the power supply output.