Capacitive Sensor Sampling Circuit for EMI Noise Suppression
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Solution Overview
Problem
Capacitive sensors often suffer from electromagnetic interference noise in their output signals, leading to inaccuracy in sensed conditions due to environmental factors, which existing technologies have not effectively addressed.
Innovation Solution
A circuit and method that randomizes the sampling instant of capacitive sensor output signals within a fixed clock period, using a sampling or demodulation circuit with a clock edge randomization component, effectively spreading interference noise outside the sensor's baseband frequency range, thereby reducing noise contributions and improving signal accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fixed clock period sampling is used, then system simplicity is maintained, but electromagnetic interference noise appears at fixed frequencies in the output signal
Solution Approach 1:
The patent applies dynamics by making the sampling instant variable rather than fixed. A random value generator creates different time offsets within the clock period for each sampling operation, causing the sampling instant to dynamically shift. This dynamic sampling approach spreads the electromagnetic interference noise across a broader frequency spectrum, reducing its impact on the sensor signal while maintaining system simplicity.
2Object-affected harmful factors
If random sampling instant is used, then electromagnetic interference noise is reduced, but duty cycle varies randomly
Solution Approach 1:
The patent uses a delay element as an intermediary between the clock signal and the sampling circuit. This delay element, controlled by a random value generator, introduces a variable time offset that randomizes the sampling instant. By placing the randomization function in this intermediary position, the system achieves noise reduction without requiring fundamental changes to the sampling circuit architecture.
3Measurement precision
If electromagnetic interference noise is present, then signal accuracy decreases, but signal and noise frequencies overlap
Solution Approach 1:
The patent applies dynamics by making the sampling instant variable rather than fixed. A random value generator creates different time offsets within the clock period for each sampling operation, causing the sampling instant to dynamically shift. This dynamic sampling approach spreads the electromagnetic interference noise across a broader frequency spectrum, reducing its impact on the sensor signal and improving signal accuracy.
Solution Approach 2:
The patent changes the timing parameter of the sampling operation by introducing random time offsets. By varying the sampling instant parameter dynamically, the system transforms the fixed-frequency noise into a spread-spectrum noise distribution, effectively separating the signal frequencies from the noise frequencies and improving measurement precision.
Data Source
AI summary
Circuits and techniques are described for reducing the impact of environmental noise and interference on the output signal of a capacitive sensor. The output signal is sampled randomly in some situations by generating a random sampling instant within a fixed clock period. The sampling is performed by a sampling or demodulation circuit. The demodulation circuit may be part of a larger circuit with various components that operate based on a fixed period clock signal.