Capacitive Touch Sensing Circuit Without Integrator Offset Error
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Solution Overview
Problem
Conventional capacitive touching apparatuses rely on integrator circuits to detect capacitance variations, which are prone to offset voltage issues and inefficiencies in detecting touch events.
Innovation Solution
The proposed capacitive touching apparatus employs an equivalent capacitor module, a comparator, a reference current generator, and a detection capacitor module to detect capacitance variations without using an integrator circuit, utilizing voltage variations from the equivalent capacitor module and reference currents to produce a detection output signal, effectively eliminating offset voltage effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an integrator circuit is used to detect capacitance variations, then the detection function is implemented, but offset voltage issues and detection inefficiency occur
Solution Approach 1:
The patent extracts and removes the integrator circuit from the detection system, replacing it with a capacitor charging/discharging module and comparison module. This extraction eliminates the offset voltage issues inherent in integrator circuits while maintaining the capacitance detection function through alternative means.
Solution Approach 2:
The patent substitutes the electrical integration mechanism with a mechanical-like charging/discharging process of capacitors. By using controlled current sources to charge capacitors and comparing their voltages, the system achieves capacitance detection without relying on the problematic integrator circuit's electrical integration function.
2Measurement precision
If an integrator circuit is used to detect capacitance variations, then capacitance detection is achieved, but offset voltage interference increases
Solution Approach 1:
The patent converts the harmful offset voltage effect into a beneficial reference comparison. By introducing a reference capacitor charged by the same current source and comparing its voltage with the detection capacitor's voltage, the system uses the offset voltage as a common reference point that cancels out in the comparison, thereby eliminating its interference.
Solution Approach 2:
The patent creates an asymmetric detection architecture where one capacitor serves as a reference and another as the detection element. This asymmetric arrangement allows the system to distinguish between the reference offset voltage and the actual capacitance variation signal, improving measurement precision by separating the harmful offset from the useful measurement.
3Productivity
If periodic oscillating signals are applied to touch capacitors for detection, then capacitance variation detection is enabled, but the detection process becomes complex and inefficient
Solution Approach 1:
The patent employs periodic action through controlled charging and discharging cycles of the capacitors. By periodically applying current to charge the capacitors and then discharging them while comparing voltages, the system achieves efficient capacitance detection without requiring complex continuous oscillating signals, simplifying the detection process while maintaining effectiveness.
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 enables accurate and efficient detection of capacitance variations, enhancing the reliability of touch event detection in capacitive touching apparatuses by eliminating the need for integrator circuits and reducing offset voltage interference.
Implementation Method 1
an equivalent capacitor module, a first comparator, a first reference current generator and a first detection capacitor module. The first terminal of the equivalent capacitor module receives a periodic driving signal, and an output voltage is produced at the second terminal of the equivalent capacitor module according to the driving signal
Implementation Method 2
The first comparator is coupled to the equivalent capacitor module, receives the output voltage and compares the output voltage with a first reference voltage so as to produce a first comparison result
Data Source
AI summary
The invention provides a capacitive touching apparatus, which includes at least an equivalent capacitor module, a first comparator, a first reference current generator, a first detection capacitor module and a selection switch module. The equivalent capacitor module receives a periodic driving signal and produces an output voltage according to the driving signal. The first comparator compares the output voltage with a first reference voltage and thereby produces a first comparison result. The first reference current generator produces a first reference current and a second reference current according to a base current, in which the first reference current generator decides whether to respectively output the first reference current and the second reference current according to the first comparison result, and the first reference current is output to the equivalent capacitor module. The first detection capacitor module produces a first detection output signal according to the second reference current.