Capacitance Sensing Circuit With Current Mirrors for Stable Touch Signals
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Solution Overview
Problem
Existing capacitance sensing circuits face challenges in reducing the influence of capacitance deviations between external and internal capacitors, leading to increased size and power consumption, as the output signal is directly proportional to the ratio of these capacitance values.
Innovation Solution
The proposed capacitance sensing circuit incorporates a buffer circuit, multiple current mirror devices, and an integral circuit with diode-connected devices to create current mirror circuits, which reduce the current drivability of pull-up and pull-down devices by a factor of N, thereby making the output voltage signal less sensitive to capacitance variations and allowing for a smaller internal capacitor, thus minimizing size and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the internal capacitor size is reduced to minimize device size, then the device size decreases, but the output signal becomes more sensitive to capacitance deviations
Solution Approach 1:
The patent changes the electrical parameters of the circuit by introducing current mirror devices with specific current drivability ratios (1/N) and diode-connected devices. These parameter changes modify the relationship between the internal and external capacitors, allowing the internal capacitor to be smaller while maintaining measurement accuracy through the transformed signal processing pathway.
Solution Approach 2:
The current mirror devices and diode-connected devices act as intermediary elements between the internal capacitor and the output signal. These intermediaries transform and condition the signal in a way that reduces sensitivity to capacitance variations, enabling the use of a smaller internal capacitor without compromising measurement precision.
2Use of energy by moving object
If the internal capacitor size is reduced to minimize power consumption, then the power consumption decreases, but the output signal becomes more sensitive to capacitance deviations
Solution Approach 1:
The patent modifies circuit parameters through the current mirror devices with 1/N current drivability and diode-connected devices, creating a signal processing pathway that allows reduced capacitor size (and thus reduced power consumption) while maintaining measurement precision through the transformed electrical characteristics.
Solution Approach 2:
The current mirror and diode-connected devices serve as intermediary components that decouple the direct relationship between capacitor size and measurement sensitivity, enabling lower power consumption with smaller capacitors while preserving accuracy through intermediate signal transformation.
3Measurement precision
If the current drivability of pull-up and pull-down devices is reduced by a factor of N, then the output voltage signal becomes less sensitive to capacitance variations, but the circuit complexity increases
Solution Approach 1:
The patent segments the signal processing function into multiple specialized components: current mirror devices with specific 1/N current drivability ratios and diode-connected devices. This segmentation allows each component to perform a specific function that collectively reduces sensitivity to capacitance variations, managing the complexity through functional decomposition.
Solution Approach 2:
The current mirror devices and diode-connected devices act as intermediary elements that transform the signal in a controlled manner. These intermediaries provide a structured pathway that reduces sensitivity to capacitance variations while organizing the complexity into manageable, functionally-defined stages.
4Measurement precision
If multiple current mirror devices and diode-connected devices are added to reduce sensitivity to capacitance deviations, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent divides the measurement function into segmented stages using multiple current mirror devices and diode-connected devices. Each segment performs a specific transformation that collectively improves measurement precision by reducing sensitivity to capacitance deviations, while the modular segmentation helps manage the overall circuit complexity.
Solution Approach 2:
The multiple current mirror devices and diode-connected devices serve as intermediary elements that systematically transform the signal through multiple stages. These intermediaries improve measurement precision through cumulative signal conditioning while organizing the complexity into a structured, multi-stage processing pathway.
Data Source
AI summary
A capacitance sensing circuit includes a buffer circuit, a modulation circuit, and an integral circuit. The buffer circuit is coupled to an external capacitor through a touch-sensing pad, and includes a pull-up device and a pull-down device. The modulation circuit includes a first current mirror device having a current drivability corresponding to one Nth (where “N” denotes a positive real number) a current drivability of the pull-up device and a second current mirror device having a current drivability corresponding to one Nth a current drivability of the pull-down device. The integral circuit integrates voltage values at an output node of the modulation circuit to output the integrated voltage values. The pull-up device and the first current mirror device constitute a current mirror circuit, and the pull-down device and the second current mirror device constitute another current mirror circuit.