Capacitive Sensing Using Orthogonal Sub-Stimulation Signals
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Solution Overview
Problem
Capacitive sensing apparatus in devices like touch panels and fingerprint scanners face interference from environmental noises, leading to sensing errors, and existing methods to improve accuracy either increase dynamic range or slow down sensing operations, resulting in higher power consumption.
Innovation Solution
The method involves transmitting a stimulation signal with multiple orthogonal sub-stimulation signals to a capacitive sensing device, detecting sub-charge signal amplitudes, and reporting capacitance values, while checking for signal corruption to enhance accuracy and noise immunity without increasing dynamic range or power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the amplitude of the stimulus is increased to increase sensing accuracy, then sensing accuracy is improved, but dynamic range requirements increase and power consumption increases
Solution Approach 1:
The stimulus signal is segmented into multiple orthogonal sub-stimulation signals with different frequencies. Each sub-stimulation signal carries a portion of the sensing information, allowing the system to achieve high sensing accuracy through signal processing rather than increasing overall stimulus amplitude, thus reducing power consumption and dynamic range requirements.
Solution Approach 2:
The system changes the frequency parameter of the stimulus signal by using multiple orthogonal frequencies instead of increasing amplitude. This parameter change allows the sensing system to distinguish between different touch points and improve accuracy through frequency discrimination rather than amplitude scaling.
2Measurement precision
If the time period for sensing is increased to increase sensing accuracy, then sensing accuracy is improved, but sensing operation speed decreases and power consumption increases
Solution Approach 1:
The sensing process is segmented into parallel channels, each operating at a different frequency. Multiple touch points can be sensed simultaneously through frequency multiplexing, which maintains high sensing accuracy without requiring extended sensing time periods, thus preserving fast operation speed.
Solution Approach 2:
The system uses periodic sub-stimulation signals at orthogonal frequencies to continuously sense multiple touch points. This periodic action at multiple frequencies enables simultaneous measurement without requiring long integration periods, maintaining both accuracy and speed.
3Measurement precision
If multiple orthogonal sub-stimulation signals are used for simultaneous capacitance sensing, then sensing accuracy and noise immunity are improved, but signal processing complexity increases
Solution Approach 1:
The patent introduces orthogonal frequency components as intermediaries to separate and identify different touch points. These frequency intermediaries act as unique identifiers for each sensing channel, allowing the system to process multiple signals simultaneously without direct interference, reducing the complexity of signal separation and 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 allows for simultaneous capacitance sensing with increased accuracy and noise immunity, reducing power consumption and improving reliability in capacitive sensing systems.
Implementation Method 1
A mutual capacitance forms when one conductor in one layer overlays another conductor in the other layer
Implementation Method 2
The stimulus is coupled onto a sensing channel (e.g. a column conductor in a touch panel) through a capacitance between the driving and sensing channels
Data Source
AI summary
Disclosed is a system and method for a capacitive sensing device. The method includes transmitting a stimulation signal to a driving channel of the capacitive sensing device. The stimulation signal includes a plurality of sub-stimulation signals. Each of the sub-stimulation signals is characterized by an amplitude and a frequency. The frequencies of the sub-stimulation signals are orthogonal. The method further includes receiving a charge signal from a sensing channel of the capacitive sensing device. The charge signal is generated from the stimulation signal through a capacitance between the driving channel and the sensing channel. The method further includes detecting, from the charge signal, a plurality of sub-charge signal amplitudes at the frequencies of the sub-stimulation signals, and reporting a value about the capacitance from the sub-charge signal amplitudes. The method benefits the capacitive sensing device for increased noise immunity, reduced dynamic range, and reduced power consumption.