Capacitance Detection Circuit for High-SNR Touch Sensing
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Solution Overview
Problem
Current capacitance detection systems face challenges in maintaining high sensitivity and signal-to-noise ratio, especially with increasing screen sizes and capacitance values, leading to circuit saturation and reduced refresh rates in touch screens.
Innovation Solution
A capacitance detecting circuit that configures the operational amplifier with a preset voltage to prevent signal loss by ensuring all current signals flow through the coupling capacitor, allowing for simultaneous mutual-capacitance and self-capacitance detection using a single circuit by changing the coding voltage position, and utilizing current signal replication and charge amplification to read full channel differential signals without losing refresh rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the screen size and capacitance values are increased, then the detection range is improved, but the circuit saturation and signal-to-noise ratio deteriorate
Solution Approach 1:
The capacitance detection is segmented into two independent modes: mutual-capacitance detection and self-capacitance detection. Each mode has its own signal path and processing circuitry, allowing the system to handle large screen capacitance values without saturation by selecting the appropriate detection mode for each region.
Solution Approach 2:
The system dynamically switches between mutual-capacitance detection and self-capacitance detection modes based on the detected capacitance values. This dynamic adaptation allows the circuit to maintain optimal signal-to-noise ratio across different screen sizes and touch conditions, preventing circuit saturation while preserving measurement precision.
2Productivity
If the refresh rate is increased, then the touch response speed is improved, but the power consumption increases
Solution Approach 1:
The system performs capacitance detection periodically at optimized intervals rather than continuously, achieving high refresh rates when needed while reducing power consumption during stable states. The detection is triggered by touch events or time-based intervals, balancing responsiveness with energy efficiency.
Solution Approach 2:
The system changes detection parameters such as integration time, sampling frequency, and amplification gain based on touch conditions and screen regions. This allows high refresh rates in critical areas while using lower rates in stable regions, optimizing the balance between touch response speed and power consumption.
3Device complexity
If a single circuit is used for both mutual-capacitance and self-capacitance detection, then the device complexity is reduced, but the detection precision may be compromised
Solution Approach 1:
The system uses a universal operational amplifier and signal processing circuit that can perform both mutual-capacitance and self-capacitance detection functions. By configuring the same circuit with different voltage inputs and connection modes, the system achieves multi-functionality without requiring separate dedicated circuits for each detection type.
Solution Approach 2:
The circuit configuration is dynamically reconfigurable through switching elements that change the connection topology and input voltages based on the desired detection mode. This dynamic reconfiguration allows a single circuit to maintain high detection precision for both mutual-capacitance and self-capacitance by optimizing its parameters for the current detection task.
Data Source
AI summary
Provided are a capacitance detecting circuit, a touch control chip, a touch detection apparatus and an electronic device. The capacitance detecting circuit, by configuring a first input side of an operational amplifier as a preset voltage, and utilizing the same characteristics of voltages at two input sides of the operational amplifier, enables that an output voltage in a touch sensor is configured as a preset voltage by a second input side of the operational amplifier, and by changing a position of a drive of a coding voltage, mutual-capacitance and self-capacitance detection can be realized with the same circuit. After replicating a single-channel current signal output by the operational amplifier into a multi-channel current signal, a current subtracting circuit is used to determine a differential signal of current signals output by two adjacent channels, and the differential signal is converted into a voltage through a charge amplifying circuit.