Charge Pump Randomization for RF Emission Reduction
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Solution Overview
Problem
Radio frequency (RF) emission from capacitive sensing devices interferes with other devices, particularly in proximity sensor systems, due to the periodic operation of charge pumps, which can cause electromagnetic interference.
Innovation Solution
A control circuit operates the charge pump at irregular intervals to transfer charge to a reservoir capacitor, randomizing the RF emission spectrum and creating targeted nulls to mitigate interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the charge pump operates at regular intervals to transfer charge to the reservoir capacitor, then the power supply to the sensing circuitry is stable, but RF emission peaks occur causing electromagnetic interference with other devices
Solution Approach 1:
The charge pump operates in periodic intervals with random variations in the on-duration and off-duration periods. This periodic yet randomized operation pattern allows the system to maintain average power delivery while disrupting the spectral peaks that cause RF interference, effectively resolving the contradiction between power stability and RF emission reduction.
Solution Approach 2:
The system dynamically changes the operational parameters of the charge pump, specifically the on-duration and off-duration periods, by introducing random variations. This parameter modification transforms the fixed periodic operation into a randomized periodic operation, which reduces RF emission peaks while maintaining adequate power supply to the sensing circuitry.
2Use of energy by moving object
If the charge pump operates continuously to ensure adequate charge transfer, then power supply requirements are met, but RF emission interference increases
Solution Approach 1:
Instead of continuous operation, the charge pump uses periodic intervals with randomized on-duration and off-duration periods. This approach maintains adequate charge transfer efficiency over time while significantly reducing RF emission interference by disrupting the continuous electromagnetic radiation pattern.
Solution Approach 2:
The system maintains continuous useful action through periodic charge transfer operations that, while interrupted, ensure adequate charge accumulation in the reservoir capacitor. The randomized periodic operation preserves the continuity of power delivery to the sensing circuitry while eliminating the harmful continuous RF emissions.
3Object-affected harmful factors
If the charge pump operates at irregular intervals to reduce RF emission peaks, then electromagnetic interference is minimized, but power delivery to the sensing circuitry becomes less predictable
Solution Approach 1:
The charge pump employs periodic operation with randomized intervals, where the on-duration and off-duration periods vary randomly but follow a structured periodic pattern. This ensures that while the exact timing is unpredictable (reducing RF peaks), the average power delivery remains reliable and adequate for the sensing circuitry operation.
Solution Approach 2:
The system incorporates feedback mechanisms that monitor the charge levels in the reservoir capacitor and adjust the periodic operation parameters accordingly. This feedback ensures that power delivery reliability is maintained even with irregular intervals, as the system can compensate for variations in charge transfer timing.
Data Source
AI summary
In an example, a processing system for an electronic device, such as a capacitive sensing device, includes a reservoir capacitor configured to store charge from a charge pump, and a control circuit configured to operate the charge pump at irregular intervals to transfer charge to the reservoir capacitor.