Synchronized Charge Pump for Capacitive Touch Screens
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Solution Overview
Problem
Existing capacitive touch screen systems face challenges in achieving high signal-to-noise ratio and efficient power consumption, particularly in mutual capacitance sensing mode, due to unsynchronized AC signals and high frequency oscillations in charge pump circuits.
Innovation Solution
A touch screen system with a synchronized charge pump circuit that operates at the same frequency as the AC drive signal, reducing power consumption and system noise by converting the load from resistive to switching capacitor, and utilizing a regenerative clocked comparator and voltage control circuit to generate an accurate supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a charge pump circuit operates at high frequency to regulate voltage accurately, then voltage regulation precision is improved, but power consumption increases and electromagnetic interference is generated
Solution Approach 1:
The charge pump circuit operates in periodic cycles synchronized with the AC drive signal frequency, switching between charging and discharging phases. This periodic operation allows the circuit to achieve adequate voltage regulation precision while operating at lower frequencies compared to continuous high-frequency switching, thereby reducing power consumption and electromagnetic interference.
Solution Approach 2:
The patent changes the operating frequency parameter of the charge pump circuit to match the AC drive signal frequency. This parameter adjustment optimizes the balance between voltage regulation precision and power consumption, allowing the circuit to operate efficiently at the specific frequency required by the touch screen system rather than using fixed high-frequency switching.
2Stability of the object's composition
If a charge pump circuit operates at high frequency to ensure stable voltage supply, then voltage stability is improved, but system noise and electromagnetic interference increase
Solution Approach 1:
The charge pump operates in synchronized periodic cycles with the AC drive signal, creating predictable switching patterns that minimize random electromagnetic noise. The periodic operation at matched frequency ensures voltage stability while reducing broadband electromagnetic interference compared to unsynchronized high-frequency switching.
Solution Approach 2:
The patent converts the potential harm of switching noise into a benefit by synchronizing the charge pump switching with the AC drive signal frequency. This synchronization causes the switching harmonics to align with the existing signal frequency, minimizing additional electromagnetic interference while maintaining voltage stability through controlled periodic operation.
3Device complexity
If a charge pump circuit operates independently without synchronization, then circuit design simplicity is maintained, but power consumption increases and signal-to-noise ratio deteriorates
Solution Approach 1:
The charge pump circuit is merged with the AC drive signal generation system by synchronizing their operating frequencies. This integration allows both circuits to share the same clock source and timing references, achieving power consumption optimization and improved signal-to-noise ratio without requiring completely independent complex control systems.
Solution Approach 2:
The AC drive signal frequency serves multiple functions: it drives the touch screen electrodes and simultaneously clocks the charge pump circuit. This multi-functionality eliminates the need for separate frequency synthesis circuits, maintaining design simplicity while achieving synchronized operation that reduces power consumption and improves signal-to-noise ratio.
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 configuration enhances power efficiency by 85-90%, reduces system noise, and minimizes electromagnetic interference, allowing for improved signal-to-noise ratio and accurate touch detection without overshoot.
Implementation Method 1
a divided version of the accurate supply voltage to a reference voltage
Implementation Method 2
a voltage control circuit configured to generate the accurate supply voltage in response to the comparison signal
Implementation Method 3
converting the load from resistive to switching capacitor
Implementation Method 4
operates at the same frequency as the AC drive signal
Data Source
AI summary
Disclosed herein is a touch screen controller including a driver circuit applying a drive signal to a drive line of a capacitive touch sensing panel. The driver circuit is powered by an accurate supply voltage. A driver supply circuit receives an input supply voltage and outputs the accurate supply voltage. The driver supply circuit includes a clocked comparator comparing a divided version of the accurate supply voltage to a reference voltage and outputting a comparison signal based thereupon. A voltage control circuit (e.g. a charge pump circuit) generates the accurate supply voltage in response to the comparison signal. The clocked comparator and voltage control circuit are both clocked by a driver supply circuit clock.