Capacitive Sensing Circuit With DAC Feedback for Noise-Resistant Detection
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Solution Overview
Problem
Conventional capacitive input devices struggle to accurately detect small changes in capacitance due to noise and environmental variations, leading to difficulties in distinguishing real signals from noise, especially with a resolution of 1% or less.
Innovation Solution
Implementing a DAC and operational amplifier system where the operational amplifier's input terminals are connected to a sensing signal line, with the DAC value adjusted to achieve a zero-volt output, and the detected value is stored for comparison with current readings to account for environmental changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional capacitive detection is used, then the device structure is simple, but the measurement precision deteriorates due to inability to distinguish real signals from noise
Solution Approach 1:
The patent applies preliminary action by storing the initial capacitance value (before object contact) in a register for later comparison. This pre-stored reference value enables the system to detect capacitance changes by comparing current readings against the baseline, thereby improving measurement precision without requiring complex differential circuitry.
Solution Approach 2:
The patent implements feedback through continuous comparison of current capacitance values with the stored initial value. The system repeatedly measures the capacitance and compares it against the reference, enabling real-time detection of changes. This feedback mechanism allows the system to distinguish actual signal changes from noise, improving detection precision while maintaining relatively simple hardware.
2Reliability
If environmental variations are not compensated, then the device operation is simple, but the reliability deteriorates due to temperature and voltage changes
Solution Approach 1:
The patent performs preliminary calibration by storing the initial capacitance value under known environmental conditions before normal operation. This pre-established reference accounts for the baseline environmental state, and subsequent comparisons can detect both object-induced changes and environmental drift, improving reliability without requiring continuous complex environmental sensing.
Solution Approach 2:
The continuous comparison mechanism provides feedback that enables the system to detect environmental variations. By repeatedly measuring and comparing capacitance values against the stored reference, the system can identify drift caused by temperature or voltage changes, thereby maintaining detection reliability while using a relatively simple feedback-based approach rather than complex environmental compensation circuits.
3Measurement precision
If the detection threshold is set low to detect small capacitance changes, then the measurement precision improves, but the reliability worsens due to increased noise interference
Solution Approach 1:
The patent uses feedback through continuous comparison of current capacitance readings with the stored initial value. This comparison approach enables the system to use low detection thresholds for high precision while maintaining reliability, because the feedback mechanism can distinguish consistent changes (real signals) from random fluctuations (noise) by analyzing trends over multiple measurement cycles rather than relying on single-threshold decisions.
Solution Approach 2:
By pre-storing the initial capacitance value, the system establishes a reference that enables precise detection of small changes. The difference between current readings and this preliminary-stored reference allows for low-threshold detection while maintaining reliability, as the system can identify genuine changes relative to the baseline rather than using absolute thresholding that is more susceptible to noise.
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
This approach enhances the detection sensitivity and accuracy of capacitive changes by continuously calibrating the initial value, improving the resolution and reliability of capacitive input devices.
Implementation Method 1
an operational amplifier within the semiconductor integrated circuit (IC); one input terminal of the operational amplifier is connected to a digital-to-analog converter (DAC); the other input terminal of the operational amplifier is connected to the sensing signal line
Implementation Method 2
a digital-to-analog converter (DAC) connected to one input terminal of the operational amplifier
Data Source
AI summary
The present invention involves replicating the existing state in a system to store in memory for detecting variations due to added factors. Based on the stored values in the memory, changes in the system are detected. A certain electronic circuit is used to extract these replicated values, and the values output from the electronic circuit are fed back. The adjusted input variables are then extracted and stored in memory.