Capacitive Sensing System Using Spread Spectrum Excitation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing capacitive sensors lack selectivity and immunity to noise and interference, and have high electromagnetic emissions, which are critical issues in human-device interface technologies such as touchscreens and proximity sensors.
Innovation Solution
A capacitive sensing system that utilizes a sinusoidal or spread spectrum excitation signal with programmable frequency and bandwidth, combined with a hybrid demodulator and analog-to-digital converter, to provide high selectivity, low electromagnetic emissions, and immunity to noise and interference, while converting capacitance values to digital format effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional capacitive sensing methods are used, then capacitance detection is achieved, but selectivity and immunity to noise and interference are poor
Solution Approach 1:
The patent employs periodic excitation signals at specific frequencies to drive the capacitive sensor. By using AC coupling and periodic modulation, the system achieves frequency selectivity that improves noise immunity while maintaining measurement accuracy through synchronous detection techniques.
Solution Approach 2:
The system changes the operating frequency parameter of the excitation signal to optimize performance. By tuning the excitation frequency and using AC coupling, the sensor achieves better selectivity and noise rejection while maintaining accurate capacitance measurement through frequency-domain separation.
2Object-affected harmful factors
If conventional capacitive sensing methods are used, then capacitance detection is achieved, but electromagnetic emissions are high
Solution Approach 1:
The patent applies AC coupling specifically at the sensor input stage to limit electromagnetic emissions locally at the source. By using capacitive coupling blocks DC and low-frequency noise while passing the AC excitation signal, the system reduces overall electromagnetic emissions while maintaining noise immunity through frequency-selective coupling.
3Reliability
If AC coupling is used to improve noise immunity, then selectivity increases, but DC current injection immunity may be affected
Solution Approach 1:
The system uses periodic AC excitation signals with specific frequencies to drive the capacitive sensor. The AC coupling capacitor blocks DC current injection while allowing the AC excitation signal to pass through, achieving both noise immunity and DC immunity simultaneously through frequency-domain separation.
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 system achieves excellent differential linearity, low power consumption, and immunity to noise and interference, with the ability to suppress AC components, making it suitable for various applications including touchscreens and proximity sensors.
Implementation Method 1
Capacitive coupling is the transfer of energy within an electrical network by means of the capacitance between circuit nodes. Capacitive coupling is typically achieved by placing a capacitor in series with the signal to be coupled.
Implementation Method 2
a demodulator coupled to the capacitance-to-amplitude converter to receive the AC signal and to the signal generator to receive the digital local oscillator signal, wherein the demodulator is configured to output a DC component proportional to the AC signal
Data Source
AI summary
A capacitive sensing system are configured to sense a capacitance value and convert the sensed capacitance value to a digital format. The capacitive sensing system provides good selectivity and immunity to noise and interference, which can be further enhanced by enabling spread spectrum excitation. In some embodiments, the capacitive sensing system utilizes a sinusoidal excitation signal that results in low electromagnetic emissions, limited to narrow frequency band. In some embodiments, the capacitive sensing system is configured to operate in a spread spectrum mode, in which the majority of the excitation signal power is carried in the assigned bandwidth. The excitation frequency and the bandwidth of the spread spectrum excitation signal are programmable in a wide range, which allows for avoiding frequency conflicts in the operating environment.