Asynchronous Capacitance-to-Digital Converter for Low-Power Touch Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitance sensing systems in user interface devices, such as touch-sensor pads and touchscreens, consume excessive power and time, making them inefficient for applications with power and speed constraints.
Innovation Solution
A capacitance-to-digital converter (CDC) system that includes a comparator coupled to sensing electrodes, a capacitive digital-to-analog converter (CapDAC) controlled by a counter through a logic circuit, and uses asynchronous logic and low-frequency oscillation to detect capacitance changes efficiently, reducing power consumption and processing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional capacitance sensing systems are used in user interface devices, then capacitance changes can be detected, but power consumption is excessive and processing time is too long
Solution Approach 1:
The patent implements periodic sampling of capacitance values at defined intervals rather than continuous monitoring. The system periodically activates the sensing electrodes and reads capacitance changes only when necessary, allowing the system to enter low-power states between measurements. This periodic action significantly reduces average power consumption while maintaining adequate detection capability for touch events.
Solution Approach 2:
The patent employs dynamic adjustment of sensing parameters based on operational conditions. The system can adaptively modify sampling rates, electrode activation patterns, and threshold levels according to the current state of the device and detected activity levels. This dynamic behavior allows the system to optimize the balance between power consumption and detection responsiveness in real-time.
2Loss of time
If conventional capacitance sensing systems are used in user interface devices, then capacitance changes can be detected, but processing time is excessive
Solution Approach 1:
The patent implements preliminary actions by pre-charging sensing electrodes to defined voltage levels and pre-configuring readout circuits before actual measurement is needed. The system prepares the sensing infrastructure in advance during low-power intervals, so that when a touch event occurs, the measurement can be performed immediately without lengthy initialization sequences, thus reducing processing time.
Solution Approach 2:
The patent employs accelerated measurement techniques that skip unnecessary intermediate steps in the capacitance measurement process. The system uses rapid charge-discharge cycles and streamlined signal processing paths to quickly capture capacitance changes, rushing through the measurement process in minimal time when events require detection, thereby reducing overall processing time.
3Speed
If high-speed capacitance detection is implemented, then processing time is reduced, but power consumption increases
Solution Approach 1:
The patent applies periodic high-speed detection only at strategically chosen intervals rather than continuously. During periodic high-speed measurement phases, the system performs rapid capacitance sampling to quickly detect touch events. Between these periodic high-speed phases, the system transitions to lower-power modes with reduced sampling rates, thus achieving fast detection capability when needed while minimizing overall power consumption.
Solution Approach 2:
The patent dynamically changes operational parameters such as sampling frequency, measurement duration, and circuit operating modes based on detected conditions. When touch events are detected or suspected, the system switches to high-speed detection parameters. When no activity is detected, the system transitions to low-power parameters with slower sampling rates, thereby adapting detection speed to actual needs and optimizing the power-speed tradeoff.
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 CDC system effectively detects capacitance changes with reduced power consumption and faster processing, optimizing performance for low-power applications like mobile devices.
Implementation Method 1
capacitance sensing systems... function by sensing electrical signals generated on electrodes that reflect changes in capacitance
Implementation Method 2
comparing the signal to a reference signal
Data Source
AI summary
An asynchronous capacitance-to-digital converter (CDC) is described that allows for very low-power operation when during inactive periods (when no conductive object is in contact or proximity to the sensing electrodes). Asynchronous operation of the CDC provides for capacitance-to-digital conversion without the use of system resources and more power intensive circuit elements.