Capacitive Touch Sensing With Switched Dual-Phase Charge Transfer
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Solution Overview
Problem
Capacitive sensing systems face challenges in noise immunity and measurement accuracy due to random telegraph signal noise and current mirror non-linearity, which affect the detection of touch or proximity.
Innovation Solution
The system employs a method of charging and discharging capacitive sensors, using multiple input terminals and transferring units with switching units to alternately couple charges to sample capacitors, and performs two conversions with half-cycle phase shifts to reduce noise impact, thereby improving noise immunity and measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional capacitive sensing is used, then the system is simple, but noise immunity and measurement accuracy deteriorate due to random telegraph signal noise and current mirror non-linearity
Solution Approach 1:
The sensing system is divided into multiple independent converting units (first converting unit and second converting unit), each capable of performing charge transfer and conversion independently. This segmentation allows parallel processing of capacitance measurements, improving accuracy through averaging while maintaining modular system architecture that doesn't excessively increase complexity
Solution Approach 2:
The system performs periodic charge transfer operations between capacitive sensors and sample capacitors through alternating phases. The first and second converting units operate in alternating cycles, with each unit performing charge transfer during its designated phase. This periodic action enables time-division multiplexing, improving measurement accuracy through multiple samples while managing system complexity through structured temporal organization
2Measurement precision
If single converting unit is used, then the system is simple, but measurement accuracy deteriorates due to unaveraged errors from noise and non-linearity
Solution Approach 1:
The first and second converting units operate in alternating periodic phases, with each unit performing charge transfer during its designated time window. This periodic operation allows two conversions to be completed in sequence, effectively doubling the conversion throughput compared to a single unit while enabling error averaging through multiple measurements
Solution Approach 2:
The system performs preliminary charge transfer operations in the first converting unit, then uses the second converting unit to perform additional charge transfer and conversion. This preliminary action approach allows errors to be averaged across multiple conversion stages, improving accuracy while maintaining efficient productivity through structured sequential processing
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
This approach enhances the accuracy of capacitance change sensing by averaging errors and reducing the impact of noise, leading to improved noise immunity and more reliable touch or proximity detection.
Implementation Method 1
Touch or proximity to the capacitive sensor is determined by detecting a capacitance change between two opposite electrodes thereof
Implementation Method 2
The capacitance between the two electrodes of the capacitive sensor is measured by charging the capacitive sensor to a predetermined voltage and measuring the amount of charges charged to the capacitive sensor. The measurement includes transferring the charges to a sample capacitor by discharging the capacitive sensor
Data Source
AI summary
A system for sensing touch or proximity include: a first number of input terminals configured to couple one or more capacitive sensors, a second number of transferring units configured to transfer charges from the one or more capacitive sensors through the first number of input terminals in transferring phases of cycles of the one or more capacitive sensor, wherein at least one of the first and second numbers is equal to or greater than two, and a first switching unit, coupled between the first number of input terminals and the second number of transferring units, configured to selectively electrically couple any one of the first number of input terminals to any one of the second number of transferring units in the transferring phases.