Switched Capacitor Integrator Circuit for Noise-Robust Touch Sensing
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Solution Overview
Problem
Capacitance measuring circuits used in touch screens for portable devices are prone to malfunctions due to noise interference from surrounding environmental changes, affecting the accuracy of touch input sensing.
Innovation Solution
A noise-robust integrator circuit is designed, comprising operational amplifiers and capacitors configured with specific switching mechanisms and feedback capacitors, which alternately integrate electric charges to cancel out noise inputs, ensuring accurate touch sensing by differentiating between noise and actual touch inputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitance measuring circuit is used to sense touch input on a capacitive touch screen, then the touch sensing function is achieved, but the circuit is susceptible to noise interference from environmental changes causing malfunctions
Solution Approach 1:
The patent divides the single integrator circuit into two separate integrators: a first integrator connected to the sensing electrode and a second integrator connected to the reference electrode. This segmentation allows independent processing of signals from both electrodes, enabling noise cancellation by comparing and subtracting the integrated values, thereby improving reliability while maintaining noise robustness
Solution Approach 2:
The patent implements feedback mechanisms in both integrators using feedback capacitors (first feedback capacitor and second feedback capacitor) that connect the output back to the inverting input terminal. This feedback is essential for maintaining the virtual ground at the inverting input terminal and ensuring accurate integration, which is critical for precise touch sensing and noise rejection
2Device complexity
If a single integrator circuit is used for capacitance measurement, then the circuit complexity is reduced, but the noise rejection capability is insufficient
Solution Approach 1:
The patent segments the measurement function into two parallel integrator circuits, each processing a separate electrode signal. This segmentation increases the measurement precision by enabling differential measurement and noise cancellation, while the overall circuit remains relatively simple using standard operational amplifier-based integrator modules
Solution Approach 2:
The patent introduces a difference amplifier as an intermediary component that receives integrated signals from both integrators and computes their difference. This intermediary stage is crucial for eliminating common-mode noise and extracting the differential touch signal, significantly improving measurement precision without requiring complex processing
3Measurement precision
If the inverting input terminal is maintained at virtual ground potential, then the integration accuracy is improved, but the circuit requires precise potential control
Solution Approach 1:
The patent employs the self-service property of the virtual ground concept, where the operational amplifier automatically adjusts its output to maintain the inverting input terminal at ground potential without requiring external control. The feedback capacitor and operational amplifier work together to self-regulate the potential, achieving high integration accuracy while avoiding complex potential control mechanisms
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 solution effectively reduces input sensing errors caused by noise, enhancing the reliability of touch screen operations in noisy environments by isolating and canceling noise components, thereby improving the accuracy of touch input detection.
Implementation Method 1
a first feedback capacitor connected between the inverting input terminal and the output terminal of the first operational amplifier, and a second feedback capacitor connected between the inverting input terminal and the output terminal of the second operational amplifier
Implementation Method 2
a first operational amplifier, and a second operational amplifier
Implementation Method 3
a first switch and a second switch connected in series between the inverting input terminals of the first and second operational amplifiers and the first terminal of the capacitor, a third switch and a fourth switch connected in series between the second terminal of the capacitor and first and second potentials
Data Source
AI summary
A switched capacitor integrator circuit is disclosed. The switched capacitor integrator circuit comprises an inverting switched capacitor integrator circuit, and a non-inverting switched capacitor integrator circuit connected to the inverting switched capacitor integrator circuit. A sampling capacitor of the inverting switched capacitor integrator circuit is shared by the non-inverting switched capacitor integrator circuit.