Charge Pump Frequency Selection for Touchscreen Noise Reduction
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Solution Overview
Problem
Capacitive touchscreens often generate undesired coherent noise due to on-chip charge pump circuits, which interferes with touch detection, especially in environments with high signal-to-noise ratios.
Innovation Solution
A capacitive touchscreen system with a charge pump circuitry that generates output signals with distortion signals superimposed, where these distortion signals are filtered out by demodulator circuitry using integer division of a synchronization signal, ensuring that the noise is minimized and does not interfere with touch detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If on-chip charge pump circuitry is used for high voltage generation, then manufacturing cost is reduced, but coherent noise is generated that interferes with touch detection
Solution Approach 1:
The patent changes the operating frequency parameter of the charge pump circuitry to a specific frequency (e.g., 1.2 MHz) that minimizes coherent noise interference. By carefully selecting and adjusting the frequency parameter, the system achieves low-cost on-chip charge pump operation while eliminating the harmful coherent noise that would otherwise interfere with touch detection.
2Reliability
If high voltage signals are used to drive capacitive touchscreen, then signal-to-noise ratio is improved, but charge pump circuitry generates coherent noise that interferes with touch detection
Solution Approach 1:
The patent adjusts the charge pump frequency parameter to a specific value (e.g., 1.2 MHz) that prevents coherent noise from falling within the touch detection frequency band. This parameter optimization allows the system to maintain high voltage driving signals for good signal-to-noise ratio while avoiding the generation of interfering coherent noise through careful frequency selection.
Solution Approach 2:
The patent converts the potentially harmful coherent noise generated by the charge pump into a beneficial situation by selecting a frequency where the noise falls outside the sensitive detection band. The charge pump's coherent output, which would normally be harmful, is instead positioned at a frequency that does not interfere with touch detection, effectively turning a harmful factor into a non-interfering element.
3Reliability
If charge pump frequency is increased to reduce noise interference, then touch detection reliability is improved, but distortion signals are generated that may interfere with demodulator circuitry
Solution Approach 1:
The patent optimizes the charge pump frequency parameter to a specific value (e.g., 1.2 MHz) that simultaneously achieves two goals: it raises the frequency enough to move coherent noise away from the touch detection band, improving reliability, while keeping it low enough to avoid generating distortion signals that would interfere with the demodulator circuitry's operating frequency.
Data Source
AI summary
Various embodiments of charge pump circuitry configured to generate output signals having first distortion signals superimposed thereon are disclosed. Demodulator input signals are also disclosed that have second distortion signals superimposed thereon. A synchronization signal is delivered to demodulator circuitry through at least first and second integer divider circuits and to charge pump circuitry through at least the first integer divider circuitry such that the first and second distortion signals have frequencies that are integer divisions of the synchronization frequency.