Capacitive Sensor Noise Cancellation via Reference Circuit and Current Conveyor
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Solution Overview
Problem
Capacitive sensor devices in electronic devices face interference from display components, such as cathode or anode layers in LED displays and Vcom layers in LCDs, which affect capacitive sensing accuracy due to capacitive coupling and noise injection.
Innovation Solution
The implementation of a reference circuit that generates a reference voltage to mitigate display noise, coupled with a current conveyor to output correction currents, effectively reduces interference in capacitive sensing by isolating the analog front end from noise injected into receiver channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If display components (cathode/anode layers in LED displays, Vcom layers in LCDs) are used in the device structure, then the device can provide display functionality, but capacitive coupling between display components and sensor electrodes causes noise injection that degrades capacitive sensing accuracy
Solution Approach 1:
A capacitor is introduced as an intermediary component between the display component and the sensor electrode. This capacitor couples the display component to the sensor electrode while isolating the analog front end from noise injected into the receiver channel, thereby maintaining display functionality while improving capacitive sensing accuracy
Solution Approach 2:
The coupling path is segmented by introducing a discrete capacitor that separates the noise source (display component) from the sensitive receiver channel. This segmentation allows the display component to operate independently while preventing noise propagation to the sensing circuitry
2Measurement precision
If a reference circuit with capacitor is added to generate reference voltage for noise mitigation, then capacitive sensing accuracy is improved, but device complexity increases
Solution Approach 1:
A reference circuit comprising a capacitor and reference voltage generator is introduced as an intermediary system. This reference circuit generates a reference voltage that compensates for noise effects, improving sensing accuracy while adding only moderate complexity through the use of standard circuit components
Solution Approach 2:
The reference circuit implements a feedback mechanism where the capacitor couples the display component to the reference voltage generator, which generates a reference voltage based on the noise conditions. This feedback loop continuously compensates for noise effects, improving accuracy justifying the added 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
This solution enhances the accuracy and reliability of capacitive sensing by minimizing the impact of display noise, thereby improving the usability and precision of input devices in electronic systems.
Implementation Method 1
a capacitor coupled at a first end to the transparent conductive layer, and a reference circuit coupled to a second end of the capacitor
Data Source
AI summary
Embodiments herein provide input devices that include a display panel on which a discrete capacitive sensor is disposed to form a capacitive sensing region. The capacitive sensor includes a plurality of sensor electrodes that are used to generate capacitive sensing signals indicating user interaction with the input device. Moreover, the input device includes analog interference detection circuitry for mitigating the negative impact of display noise on capacitive sensing. In one embodiment, the input device includes a reference circuit which is capacitively coupled to a display noise source and outputs a reference voltage that biases a charge integrator in a receiver channel used for capacitive sensing. In another embodiment, the input device includes a current conveyor coupled to an idle transmitter electrode of the sensor electrodes which outputs a correction current to a receiver channel to cancel a display noise current injected into the receiver channel.