Capacitive Sensor Interface With Four-Sample Noise Rejection
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Solution Overview
Problem
Existing capacitive touch sensor circuits are inadequate in rejecting medium frequency noise, such as that from switching devices, leading to false touch triggers and errors due to uncorrelated noise between consecutive samples.
Innovation Solution
A novel capacitive touch sensor circuit and signal processing method that involves taking four consecutive samples during alternating integration phases, generating a composite signal (Vcomp) with a 50% duty cycle centered at 0V, which effectively isolates medium frequency noise, allowing for its detection and elimination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional capacitive sensor circuits are used, then basic touch detection is achieved, but medium frequency noise from switching devices causes false triggers and errors
Solution Approach 1:
The patent divides the sampling process into four distinct consecutive samples (S1, S2, S3, S4) taken during alternating integration phases. This segmentation allows the system to capture noise characteristics at different time points and frequencies, enabling subsequent noise identification and elimination through comparison and processing of the segmented samples.
Solution Approach 2:
The patent implements periodic sampling at four distinct time points within each measurement cycle, alternating between positive and negative integration phases. This periodic action creates a structured pattern that allows medium frequency noise to manifest differently across samples, making it detectable and eliminable through the composite signal generation process.
2Reliability
If four consecutive samples are taken during alternating integration phases, then medium frequency noise is isolated and eliminable, but device complexity increases
Solution Approach 1:
The patent uses the four consecutive samples as feedback to generate a composite signal that highlights medium frequency noise characteristics. By comparing and processing the feedback from multiple samples taken at different phases, the system can identify and eliminate noise without requiring complex external filtering circuits.
Solution Approach 2:
The patent introduces a composite signal (Vcomp) as an intermediary that combines information from four separate samples. This intermediary signal serves as a mediator that isolates medium frequency noise components, allowing the system to eliminate noise through straightforward processing of the composite signal rather than directly processing individual noisy samples.
3Device complexity
If conventional single-sample measurement is used, then processing is simple, but false touches are triggered by noise
Solution Approach 1:
The system uses feedback from four consecutive samples to generate a composite signal that reveals medium frequency noise patterns. This feedback mechanism allows the system to maintain simple processing logic while significantly improving measurement precision by using multiple samples to identify and eliminate false triggers caused by 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
The solution significantly improves noise immunity by generating a signal that isolates medium frequency noise, reducing false triggers and enhancing the accuracy of capacitive touch sensing systems.
Implementation Method 1
The amount of charges is proportional to the mutual capacitance Cxy between the X and Y electrodes of each coplanar capacitor
Implementation Method 2
The driver applies a square pulse Vr of determined amplitude to the electrodes 30 of each line (or column) of the matrix in order to inject a predetermined reference charge
Implementation Method 3
The block 40 is a low pass filter. Its purpose is to remove high frequency noise components from the measurement without significantly attenuating the transferred signal
Data Source
Figure 1~2
Figure 3a
Figure 3b
AI summary
Electronic interface and method for reading a capacitive sensor that includes one input capacitor (30) or several input capacitors, in which the capacitive sensor is excited with a two-level voltage (V low , V high ) and read by a charge-sense amplifier whose output is sampled in four successive instants. An evaluation unit (333) is arranged to compute two difference values (V12, V34) between two pairs of samples corresponding to different voltage levels and to combine said difference values into an output value (V_out_raw) proportional to the charge transferred to the input of the charge-sense amplifier and an error value (error_bit) sensitive to a time derivative of a noise current di n /dt.