Self-Capacitance Detection Circuit With Base Capacitance Offsetting
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Solution Overview
Problem
Capacitive touch screens with flexible screens face low self-capacitance detection sensitivity due to high base capacitance and small capacitance variations, leading to detection circuit saturation and noise interference, resulting in low accuracy.
Innovation Solution
A circuit with a control module, driving module, and offsetting module that charges and discharges capacitors through specific branch circuits to offset base capacitance, enhancing capacitance variation detection and sensitivity by eliminating the influence of base capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the detection electrode is placed closer to the system ground to reduce screen thickness, then the base capacitance increases, but the capacitance variation becomes smaller relative to base capacitance, reducing detection sensitivity
Solution Approach 1:
The patent extracts the base capacitance component from the total capacitance measurement by introducing a reference capacitor with matching base capacitance. The differential amplifier subtracts the reference capacitor's voltage (representing base capacitance) from the detection electrode's voltage, isolating only the capacitance variation signal for measurement.
Solution Approach 2:
The patent changes the measurement parameter from absolute capacitance to capacitance variation by using differential measurement. The system measures the change in capacitance (ΔC) rather than the total capacitance (C0 + ΔC), where C0 is the large base capacitance. This parameter transformation allows sensitive detection of small changes against a large background.
2Measurement precision
If a high circuit gain is used to amplify small capacitance variation signals, then the detection capability improves, but the detection circuit tends to saturate due to high base capacitance
Solution Approach 1:
The patent extracts only the relevant signal component (capacitance variation) before amplification by using a differential amplifier configuration. The reference capacitor path and detection electrode path are processed differentially, removing the common-mode base capacitance signal, so that subsequent amplification only needs to handle the small variation signal without being affected by the large base capacitance.
Solution Approach 2:
The patent creates a copy of the base capacitance using a reference capacitor that mirrors the detection electrode's base capacitance characteristics. This reference copy is used in the differential amplifier to subtract out the base capacitance effect, allowing the amplification stage to focus solely on the capacitance variation without saturation from the large base signal.
3Adaptability or versatility
If the sensing area is reduced to accommodate metal-mesh detection electrode, then the screen flexibility improves, but the capacitance variation signal becomes smaller, making it more susceptible to noise
Solution Approach 1:
The patent implements a feedback mechanism through the offsetting module that continuously monitors and compensates for baseline shifts and noise. The system uses the reference capacitor to provide feedback about environmental changes and noise conditions, allowing the differential amplifier to maintain accurate measurement of capacitance variation despite small signal levels.
Solution Approach 2:
The patent creates a reference copy of the detection environment using the reference capacitor, which experiences the same noise and environmental conditions. By differentiating between the detection electrode signal and the reference capacitor signal, the system cancels out common noise components, effectively filtering noise from the small capacitance variation signal.
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
Improves the sensitivity and accuracy of self-capacitance detection by reducing the impact of base capacitance, allowing for better detection of capacitance variations and enhancing the signal-to-noise ratio.
Implementation Method 1
the principle of self-capacitance detection is that a capacitor will be formed between a detection electrode and system ground
Implementation Method 2
the charge transfer module being configured to convert charge of the detection capacitor after the charge offsetting to generate an output voltage
Implementation Method 3
the offsetting module comprises a first offset resistor and a second offset resistor
Data Source
Figure 1A~1B
Figure 1C
Figure 2A
AI summary
The present disclosure provides a circuit for capacitance detection, a touch chip, and an electronic device, including: a control module, a driving module, an offsetting module, and a charge transfer module, the driving module being configured to positively charge a capacitor to be detected through a first charging branch circuit, or negatively charge the capacitor to be detected through a second charging branch circuit under the control of the control module; the offsetting module being configured to offset base capacitance of the capacitor to be detected through a first offsetting branch circuit under the control of the control module, or offset the base capacitance of the capacitor to be detected through a second offsetting branch circuit under the control of the control module; the charge transfer module being configured to transfer a charge on the capacitor to be detected to generate an output voltage. The circuit for capacitance detection improves the sensitivity of self-capacitance detection, and finally improves the accuracy of the self-capacitance detection.