Capacitance Evaluation Circuit With Shared ADC for Touch Sensing
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Solution Overview
Problem
Conventional capacitance evaluation circuits are not precise enough to detect capacitance variations in capacitive touch panels, leading to suboptimal user interaction and increased device complexity and cost.
Innovation Solution
A capacitance evaluation circuit that includes a capacitor under test, a sensor, a multiplexer, and an analog-to-digital converter (ADC) to convert capacitance and capacitance variations into digital signals, allowing for precise detection and sharing of ADC resources with touch screens to reduce circuit area and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional capacitance evaluation circuits are used, then the device structure is simple, but the measurement precision of capacitance variation is insufficient
Solution Approach 1:
The evaluation period is divided into distinct phases: a first evaluation period for evaluating a first capacitance value, and a second evaluation period for evaluating a second capacitance value. This temporal segmentation allows precise measurement of capacitance variations without requiring complex simultaneous measurement circuits.
Solution Approach 2:
The circuit performs periodic evaluation of capacitance values at different evaluation periods. By alternating between evaluating the first capacitance value and the second capacitance value in separate periods, the system achieves high measurement precision using simple sequential measurement rather than complex simultaneous measurement.
2Ease of manufacture
If separate ADCs are provided for touch screen and sensor, then the measurement precision is sufficient, but the device area and cost increase
Solution Approach 1:
A single analog-to-digital converter is designed to serve multiple functions: it converts analog signals from both the touch screen capacitor and the sensor capacitor. The converter alternates between evaluating the first capacitance value (touch screen) and the second capacitance value (sensor) during different evaluation periods, eliminating the need for separate ADCs while maintaining measurement precision.
Solution Approach 2:
The shared ADC operates in periodic cycles, dedicating the first evaluation period to converting the touch screen capacitance signal and the second evaluation period to converting the sensor capacitance signal. This time-division multiplexing approach allows one ADC to perform the work of two separate converters, reducing device area and cost without sacrificing measurement accuracy.
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
Enables precise detection of capacitance changes in capacitive touch panels, enhancing user interaction and reducing device complexity and cost by sharing ADC resources with touch screens.
Implementation Method 1
the capacitance of the capacitor under test is changed due to the user's operation. Thus, the user's operation can be detected.
Implementation Method 2
an analog-to-digital converter (ADC), coupled to the multiplexer, converting one of the voltage under test and the sensing signal into a digital output signal
Data Source
AI summary
A capacitance evaluation circuit includes a capacitive voltage divider, an analog-to-digital converter (ADC) and a processing module. The capacitive voltage divider includes a switch circuit, a known capacitor and a capacitor under test. The switch circuit is controlled by first and second clock signals. A voltage variation at a first terminal of the known capacitor is coupled to a first terminal of the capacitor under test based on a conduction state of the switch circuit. The ADC converts a voltage on the first terminal of the capacitor under test into a digital signal. The processing module detects a capacitance and a capacitance variation of the capacitor under test according to the digital signal from the ADC and a parameter of the ADC.