Full-Wave Synchronous Rectification for Capacitive Sensing
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Solution Overview
Problem
Capacitance sensing systems using half-wave rectification have low immunity to low frequency noise, leading to obscured touch detection and false touch indications due to power line noise and audio noise interference.
Innovation Solution
Implementing full-wave synchronous rectification using two integrating capacitors associated with modulators to measure self-capacitance of a capacitive-sense array, where both charge and discharge currents from consecutive half-waves of a full-wave signal are utilized to improve noise immunity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If half-wave rectification is used to measure capacitance, then the circuit complexity is reduced, but noise immunity deteriorates leading to obscured touch detection and false touch indications
Solution Approach 1:
The patent divides the rectification process into two separate half-wave rectifiers that process consecutive half-waves of the input signal. Each half-wave rectifier is associated with its own integrating capacitor, allowing independent processing of positive and negative cycles. This segmentation enables the system to capture both charge and discharge current information, improving noise immunity while maintaining manageable circuit complexity through modular design.
Solution Approach 2:
The patent utilizes periodic action by processing consecutive half-waves of the input signal in sequence. The first half-wave is processed by a first half-wave rectifier and the second half-wave by a second half-wave rectifier. This periodic processing of alternating half-waves allows the system to accumulate information over multiple cycles, improving measurement reliability and noise rejection while maintaining a relatively simple circuit structure.
2Measurement precision
If full-wave synchronous rectification with two integrating capacitors is implemented, then noise immunity and measurement accuracy are improved, but device complexity increases
Solution Approach 1:
The patent merges the functionality of two half-wave rectifiers into a coordinated full-wave synchronous rectification system. Both half-wave rectifiers operate simultaneously on consecutive half-waves of the input signal, and their outputs are combined to provide a complete rectified waveform. This merging approach improves measurement precision by capturing full-wave information while the shared clock signal and coordinating logic keep the overall complexity manageable.
Solution Approach 2:
The patent implements feedback mechanisms where the outputs of the two half-wave rectifiers are processed and fed back to update the capacitance measurement. The integrating capacitors accumulate charge information from both half-waves, and this accumulated information is used to calculate the total capacitance value. This feedback process continuously refines the measurement, improving accuracy while the systematic feedback structure helps organize the circuit complexity.
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
Enhances the ability to detect touch events by significantly reducing noise interference, thereby improving the reliability of capacitance measurements and eliminating false touch indications.
Implementation Method 1
measuring a self-capacitance of a capacitive-sense array by performing a full-wave synchronous rectification using two integrating capacitors
Implementation Method 2
using a first integrating capacitor associated with a first modulator and a second integrating capacitor associated with a second modulator
Data Source
AI summary
An apparatus and method to measure a self-capacitance of a capacitive sense array is described. The apparatus includes a first integrating capacitor, a first modulator, a second integrating capacitor, and a second modulator. The first modulator is operatively coupled to the first integrating capacitor. The second modulator is operatively coupled to the second integrating capacitor. The first modulator in conjunction with the first integrating capacitor and the second modulator in conjunction with the second integrating capacitor measure a self-capacitance of a capacitive-sense array by performing a full-wave synchronous rectification.