Capacitive Sensing Circuit With Adaptive Frequency for Noise Reduction
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Solution Overview
Problem
Capacitive sensors suffer from noise and jitter issues, which affect their sensing sensitivity and reliability, and require low power and low leakage current during idle periods, necessitating a low-noise and low-power solution.
Innovation Solution
A capacitive sensing system that uses two excitation signals of variable frequencies with a phase shift to modulate the sensor, allowing for iterative frequency adjustments to determine the closest frequency that triggers a comparator, thereby increasing the signal-to-noise ratio and reducing noise and jitter effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the excitation frequency is held at a constant value, then the system operation is simple, but the signal-to-noise ratio is low and noise/jitter effects are prominent
Solution Approach 1:
The patent applies dynamics by transitioning from a static constant excitation frequency to a dynamic variable excitation frequency. The sensing circuit iteratively adjusts the excitation frequency around a nominal value based on feedback from the output signal, allowing the system to adapt to noise conditions and optimize the signal-to-noise ratio dynamically rather than operating at a fixed frequency point.
Solution Approach 2:
The patent changes the excitation frequency parameter dynamically during operation. By varying the frequency around a nominal value and selecting frequencies that maximize the output signal while minimizing noise/jitter effects, the system improves sensing reliability without requiring complete system redesign.
2Measurement precision
If the excitation frequency is varied to improve signal-to-noise ratio, then the noise and jitter effects are reduced, but the system complexity increases
Solution Approach 1:
The patent implements feedback by using the output signal from the capacitive sensor to guide frequency adjustments. The sensing circuit monitors the output signal characteristics and iteratively modifies the excitation frequency based on this feedback, enabling automatic optimization of measurement precision without manual intervention or complex external equipment.
Solution Approach 2:
The sensing circuit performs self-service by autonomously adjusting its own excitation frequency based on the sensor output. The system uses its own operational parameters (output signal) to control its own behavior (frequency selection), eliminating the need for separate calibration equipment or external optimization systems.
3Duration of action of stationary object
If the capacitive sensor is left idle for long periods, then the shelf time is extended, but the leakage current increases power consumption
Solution Approach 1:
The patent applies periodic action by implementing a sleep mode that periodically activates the sensing circuit only when sensing is required. During idle periods, the circuit remains dormant with minimal power consumption, and is activated periodically or on-demand to perform sensing operations, thus extending effective shelf time while minimizing energy loss.
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 enhances the gain and signal-to-noise ratio, improving the performance and reliability of capacitive sensing by reducing noise and jitter, while also enabling self-tuning for optimal operation with different sensors.
Implementation Method 1
capacitive sensors can be used in many applications. For example, in the automotive industry, capacitive accelerometers can be installed in a tire-pressure monitoring system (TPMS) to measure acceleration of an automotive
Implementation Method 2
The excitation circuit may include a first output terminal and a second output terminal. The excitation circuit may be configured to provide a first signal of a first frequency to the capacitive sensor via the first output terminal
Data Source
AI summary
A capacitive sensing system may include a capacitive sensor and a sensing circuit. The sensing circuit may include an excitation circuit, a monitoring circuit, and a control circuit. The excitation circuit may provide a first signal of a first frequency and a second signal of a second frequency to the capacitive sensor to generate a third signal. The monitoring circuit may receive the third signal and generate an output signal based on the third signal. Based on the output signal from the monitoring circuit, the control circuit may control the first frequency of the first signal and/or the second frequency of the second signal to determine a value of the third signal.