Touch Capacitance Sensing with Base Capacitance Compensation
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Solution Overview
Problem
Capacitive touch sensors face challenges in accurately measuring small changes in capacitance due to noise susceptibility and base capacitance drift, limiting their precision and reliability.
Innovation Solution
A touch panel controller system with a capacitance-to-voltage converter that generates gain and offset control signals to compensate for base capacitance, using a combination of transmission gates, DACs, and an amplifier to accurately measure touch capacitance, and incorporates noise cancellation through correlated double sampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a 10-bit SAR ADC is employed to digitize the measurement, then the touch capacitance measurement can be performed, but the measurement is limited to approximately the 5 least significant bits due to small touch capacitance changes (0.5%), resulting in high susceptibility to error due to noise
Solution Approach 1:
The system performs preliminary action by measuring the base capacitance before the actual touch measurement and using this information to adjust the gain and offset of the ADC. This preliminary measurement allows the system to compensate for the large base capacitance and focus the ADC's resolution on the small touch-induced capacitance changes, thereby improving measurement precision and reliability
Solution Approach 2:
The system dynamically changes the gain and offset parameters of the ADC based on the measured base capacitance. By adjusting these parameters, the system optimizes the ADC's measurement range to match the small touch capacitance variations, converting a fixed-resolution system into an adaptive one that maintains high precision across different operating conditions
2Measurement precision
If conventional touch sensors are used, then the base capacitance can be measured, but the base capacitance drifts over time, creating further errors in touch capacitance measurement
Solution Approach 1:
The system implements feedback by continuously monitoring the base capacitance and using this information to adjust the measurement parameters in real-time. The measured base capacitance feeds back into the gain and offset adjustment mechanism, allowing the system to compensate for drift and maintain accurate touch capacitance measurements over time
Solution Approach 2:
The system performs preliminary measurement of the base capacitance before each touch detection cycle and uses this preliminary information to calibrate the measurement system. This preliminary action compensates for any drift that has occurred, ensuring that subsequent measurements remain accurate despite changes in the base capacitance over time
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 effectively compensates for base capacitance and reduces noise, enabling accurate measurement of small touch capacitance changes and enhancing the reliability of capacitive touch sensors.
Implementation Method 1
an capacitance-to-voltage converter that receives a clock signal and that is coupled to the interface, wherein the capacitance-to-voltage converter generates gain control and offset signals
Data Source
AI summary
A method for measuring for generating a touch capacitance measurement is provided. Gain and offset control signals are generated, where the gain and offset control signals are adjusted to compensate for base capacitance of a touch sensor. The gain control signal is applied to a touch sensor during a first phase of a clock signal, and the offset control signal is applied to an output circuit during a second phase of the clock signal. The output circuit is coupled to the touch sensor during the second phase of the clock signal. The touch capacitance measurement is generated by compensating for the base capacitance with the gain and offset control signals, and a gain is applied to the touch capacitance measurement.