Capacitance Sensing Circuit Noise Cancellation
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Solution Overview
Problem
Capacitance-type touch screens face accuracy issues due to electrical noise from wireless communications and display modules, which interfere with the detection of capacitance changes during touch inputs.
Innovation Solution
A capacitance sensing apparatus with a driving circuit unit and a buffer unit featuring switches that operate at different cycle times, and integration circuit units with output voltages of positive and negative potentials based on a common voltage, to offset noise and improve capacitance measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If capacitance-type touch screens are used to enable multi-touch and various input methods, then input versatility and gesture recognition are improved, but sensitivity to electrical noise from wireless communications and display modules increases
Solution Approach 1:
The patent applies noise cancellation technology that uses the harmful electrical noise as a reference signal to generate an opposite-phase cancellation signal. The noise sensing unit detects noise from wireless communications and display modules, and the noise cancellation unit generates a counter-signal that destructively interferes with the original noise, converting the harmful noise into a beneficial cancellation effect that protects capacitance measurements.
Solution Approach 2:
The patent introduces an intermediary noise cancellation circuit between the display module and the capacitance sensing circuit. This intermediary system includes noise sensing units that detect noise signals, and noise cancellation units that process and generate opposite-phase signals to cancel the noise before it reaches the sensitive capacitance measurement circuitry, thereby isolating the harmful noise from the measurement system.
2Measurement precision
If switches in the sensing circuit operate at the same cycle as the driving signal, then signal accuracy is improved, but noise from wireless communications and display modules cannot be offset
Solution Approach 1:
The patent implements periodic action by operating switches in the sensing circuit at different cycles than the driving signal cycle. Specifically, switches are controlled to operate at a second cycle that is different from the first cycle of the driving signal, creating a time-separated periodic operation that allows noise cancellation to function effectively while maintaining accurate capacitance detection.
Solution Approach 2:
The patent employs feedback mechanisms where noise sensing units continuously monitor the noise environment, and noise cancellation units adjust their operation based on the detected noise levels. This feedback loop ensures that the noise cancellation signal is dynamically adapted to match the actual noise conditions, maintaining measurement precision while suppressing electrical noise interference.
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 solution effectively minimizes noise interference, enhancing the accuracy of touch input coordinate detection and gesture recognition in capacitance-type touch screens by stabilizing the voltage applied to capacitors and reducing sensitivity to noise.
Implementation Method 1
a first operational amplifier having an inverting terminal connected to a first switch; and a second operational amplifier having an inverting terminal connected to a second switch
Implementation Method 2
a driving circuit unit applying a driving signal having a predetermined cycle to a first capacitor; and a sensing circuit unit sensing a change in capacitance generated in the first capacitor
Data Source
AI summary
There is provided a capacitance sensing apparatus including a driving circuit unit applying a driving signal to a first capacitor at a predetermined interval; and a sensing circuit unit sensing a change in capacitance generated by the first capacitor based on the driving signal, in which a portion of a plurality of switches included in the sensing circuit unit operate at a first interval, the same as the interval of the driving signal, and remaining switches among the plurality of switches operate at a second interval, different from the first interval.