Capacitance measurement circuit and touch detection apparatus
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Solution Overview
Problem
Capacitance detection circuits in electronic devices face challenges in improving detection performance, particularly in distinguishing capacitance changes caused by user interactions, which affects the accuracy and reliability of touch detection.
Innovation Solution
A capacitance detection circuit that includes a first charging and discharging circuit for the capacitor to be detected, a second charging and discharging circuit for a calibration capacitor, an analog-to-digital conversion circuit to sample voltage differences, and a digital processing circuit to detect capacitance changes by analyzing the energy value of the fundamental frequency of the sampled data, thereby enhancing signal-to-noise ratio and reducing noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional capacitance detection methods are used, then the detection circuit can identify capacitance changes, but the detection precision is insufficient due to noise interference
Solution Approach 1:
The patent applies periodic charging and discharging operations to the capacitor, creating oscillating voltage signals that can be analyzed through frequency domain transformation. This periodic excitation allows the system to distinguish the fundamental frequency signal from noise components, thereby improving measurement precision while suppressing noise interference
Solution Approach 2:
The patent implements periodic charging and discharging cycles with multiple periods, where each period consists of charging phase and discharging phase. By performing multiple periodic measurements and analyzing the fundamental frequency components through Fourier transform, the system enhances signal-to-noise ratio and achieves more precise capacitance detection
Solution Approach 3:
The patent transforms the detection approach by changing from direct voltage measurement to frequency domain analysis. By applying Fourier transform to convert time-domain voltage signals into frequency-domain representations, the system can identify and measure the fundamental frequency amplitude, which directly correlates to capacitance value while filtering out noise
2Reliability
If the detection circuit uses simple voltage sampling, then the circuit complexity is low, but the detection performance is insufficient
Solution Approach 1:
The patent replaces complex analog signal processing circuits with digital signal processing. By using an analog-to-digital converter to sample voltage signals and then applying digital Fourier transform algorithms, the system achieves high detection reliability while keeping the hardware circuit relatively simple. The complexity is shifted from analog circuit design to software algorithm implementation
Solution Approach 2:
The patent introduces an analog-to-digital converter as an intermediary component between the capacitive sensor and the processing unit. This intermediary enables the system to work with digital signals throughout the processing chain, allowing for more reliable and flexible signal analysis through digital algorithms while maintaining manageable circuit complexity
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 proposed solution improves the detection performance of capacitance changes, allowing for more accurate and reliable touch detection by effectively distinguishing between useful signals and interference, leading to enhanced user interaction experiences in electronic devices.
Implementation Method 1
a capacitor is formed between a detection electrode and ground, when a conductor (such as a finger) approaches or touches the detection electrode, a capacitance between the detection electrode and the ground changes
Implementation Method 2
an analog-to-digital conversion circuit, configured to continuously sample a voltage difference between the capacitor to be detected and the calibration capacitor in a charging or discharging process to obtain sampled data
Implementation Method 3
the digital processing circuit is configured to detect the capacitance of the capacitor to be detected according to an energy value of a fundamental frequency of the sampled data wherein the digital processing circuit includes a digital demodulator, where the digital demodulator is configured to perform digital quadrature demodulation or Fourier transform on the sampled data to obtain the energy value of the fundamental frequency
Data Source
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AI summary
Provided is a capacitance detection circuit (100), which has better detection performance. The capacitance detection circuit (100) includes: a first charging and discharging circuit (110) configured to perform charging or discharging on a capacitor to be detected (111); a second charging and discharging circuit (120) configured to perform charging or discharging on a calibration capacitor (121); an analog-to-digital conversion circuit (130) configured to continuously sample a voltage difference between the capacitor to be detected (111) and the calibration capacitor (121) in a charging or discharging process to obtain sampled data; and a digital processing circuit (140) configured to detect a capacitance of the capacitor to be detected (111) according to the sampled data.