Capacitive Touch Noise Blanking via Digital Filter Inhibition
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Solution Overview
Problem
Capacitive touchscreen systems face disruptions due to impulsive RF noise, which causes digital filters to 'ring', masking touch signals or indicating false touches, leading to inaccurate touch tracking.
Innovation Solution
A capacitive touchscreen system with a noise disruption detector and clock control logic circuitry that inhibits digital filter operation during excessive noise, employing a CPU and firmware to configure clock control logic to prevent filter ringing, allowing for quick recovery and accurate touch tracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital filters are used to process digitized touch signals, then measurement precision is improved, but impulsive RF noise causes filter ringing that masks touch signals and creates false touches
Solution Approach 1:
The system performs preliminary detection of impulsive RF noise events before they can affect the digital filters. The noise detection circuit identifies noise bursts and triggers a blanking signal that prevents the digital filters from processing noisy data, thereby preventing filter ringing before it occurs.
Solution Approach 2:
A noise detection circuit and clock control logic act as intermediaries between the noisy input signals and the digital filters. These intermediary components detect noise events and control the clock signal to the digital filters, preventing noisy signals from entering the filtering stage and causing ringing.
2Productivity
If the system continues normal operation during impulsive noise events, then productivity is maintained, but touch tracking accuracy deteriorates due to filter ringing
Solution Approach 1:
The system uses periodic sampling and continuous monitoring of the input signals for impulsive noise events. The noise detection circuit periodically checks for noise bursts and dynamically controls the digital filter operation, allowing the system to maintain productivity during normal operation while ensuring accuracy by pausing filter processing during noise events.
3Speed
If the digital filter operates continuously, then response time is reduced, but false touch signals increase during noise events
Solution Approach 1:
The system implements feedback through the noise detection circuit that continuously monitors the input signals and provides control signals to the clock control logic. This feedback mechanism allows the system to rapidly respond to noise events by stopping digital filter operation, minimizing false touches while maintaining quick response to legitimate touch inputs.
Data Source
AI summary
Disclosed are various embodiments of a capacitive touchscreen or touch panel system comprising a controller operably connected to a first plurality of drive electrodes and a second plurality of sense electrodes. The controller includes a noise disruption detector circuit, a user noise source detector/anticipator circuit, clock control logic circuitry operably connected to the noise disruption detector circuit and to the user noise source detector/anticipator circuit, at least one static-clocked digital filter circuit operably connected to and controlled by the clock control logic circuitry, a central processing unit (CPU) operably connected to the clock control logic circuitry, firmware operably connected to the CPU; and touch position circuitry configured to deliver signals indicative of touch positions on the touchscreen to a host controller. The controller is configured to employ at least one of the CPU and the firmware to cause the clock control logic circuitry to inhibit operation of the digital filter circuit in response to a signal representative of excessive noise levels being provided by either the noise disruption detector circuit or the user noise source detector/anticipator circuit.