Capacitance Sensor Noise Rejection Using Differential Accumulation
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Solution Overview
Problem
Capacitive touch interfaces face significant noise interference from power supply conduction and external radiation, which affects the accuracy of capacitance sensing, especially in noisy environments.
Innovation Solution
The implementation of a capacitance sensor with a noise rejection mechanism that uses a charger and sampler to apply varying voltages to the capacitance, an accumulator to incrementally and decrementally process sample signals, and a noise cancellation module to cancel out noise frequencies below the sensor's operation rate, while using a spread spectrum clock to reduce high-frequency noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If capacitance sensing is performed in noisy environments, then the sensor can operate in practical applications, but noise from power supply conduction and external radiation degrades measurement accuracy
Solution Approach 1:
The patent segments the sensing operation into multiple phases (sampling phase, hold phase, transfer phase) and uses separate capacitors for different functions (sampling capacitor, hold capacitor, transfer capacitor). This segmentation allows noise to be isolated and rejected during specific phases while maintaining accurate capacitance measurement during others.
Solution Approach 2:
The patent changes the timing parameters and voltage levels dynamically during different phases of the sensing cycle. By varying the clock signals and voltage states of switches at different times, the system can reject noise at frequencies below the sensor's operation rate while maintaining measurement accuracy.
2Reliability
If noise rejection mechanisms are added to the capacitance sensor, then noise cancellation capability is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple functions into a single integrated circuit block. The capacitance sensor integrates the charging circuit, sampling circuit, holding circuit, and transfer circuit into one unified structure, reducing overall system complexity while maintaining noise rejection capabilities.
Solution Approach 2:
The patent uses periodic clock signals to control the switching between different operational phases. This periodic action simplifies the control logic by using regular timing sequences rather than complex continuous control, reducing device complexity while achieving effective noise rejection through phase-based separation.
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 effectively cancels noise at frequencies below the sensor's operation rate and reduces high-frequency noise, enhancing the accuracy of capacitance sensing and improving the sensor's performance in noisy environments.
Implementation Method 1
an accumulator to incrementally and decrementally process sample signals, and a noise cancellation module to cancel out noise frequencies below the sensor's operation rate
Implementation Method 2
using a spread spectrum clock to reduce high-frequency noise
Implementation Method 3
a capacitance sensor with a noise rejection mechanism that uses a charger and sampler to apply varying voltages to the capacitance
Data Source
AI summary
A sensor for providing an output signal that is a function of a sensed capacitance, in a touch interface for example. The sensor includes a charger for repetitively applying first and second voltages to charge the sensed capacitance to first and second charge values in first and second phases respectively. A sampler provides first and second sample signals that are a function of the first and second charge values respectively. An accumulator uses an accumulator signal to provide the output signal. The accumulator repetitively uses the first sample signal incrementally and the second sample signal decrementally in providing the accumulator signal. The accumulator signal is a progressive function of the sensed capacitance but tends to cancel a noise in the first and second sample signals at frequencies less than a repetition rate of operation of the accumulator.