Touch Screen Controller Offset Cancellation Circuit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive touch sensing devices face challenges in accurately sensing touch inputs due to offset capacitance, which can lead to reduced sensitivity and increased noise, affecting the dynamic range of sensing signals.
Innovation Solution
Incorporating an offset cancellation circuit and charge amplifier in the touch screen controller to cancel offset capacitance, and using a self-capacitance sensing mode with a driving voltage equal to or greater than the input voltage to enhance the sensitivity of touch input detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If offset capacitance is present in the touch screen panel, then the basic circuit operation is maintained, but the sensitivity of touch input detection is reduced and noise increases
Solution Approach 1:
The patent extracts and separates the offset capacitance component from the total capacitance measurement by introducing a dedicated offset cancellation circuit. This circuit measures and subtracts the offset capacitance value from the total capacitance signal, isolating the genuine touch input signal from the parasitic offset component, thereby improving measurement precision without affecting the basic panel operation
Solution Approach 2:
The patent introduces an intermediary offset cancellation circuit between the touch screen panel and the sensing system. This intermediary component acts as a mediator that processes the raw capacitance signal by removing the offset capacitance contribution before the signal is used for touch detection, thus reducing noise and improving sensitivity without requiring changes to the basic panel structure
2Reliability
If offset capacitance is not cancelled, then the device structure remains simple, but the dynamic range of sensing signals is reduced
Solution Approach 1:
The patent segments the capacitance sensing function into distinct components: offset capacitance measurement, offset cancellation processing, and genuine touch signal detection. By dividing the sensing task into separate functional blocks within the controller, the system can maintain reliable dynamic range while managing circuit complexity through modular design
Solution Approach 2:
The patent performs preliminary action by measuring and cancelling offset capacitance before the actual touch detection process. The offset cancellation circuit pre-processes the signal by establishing a baseline offset value and subtracting it from subsequent measurements, ensuring that the full dynamic range is available for genuine touch input detection without being consumed by offset variations
3Measurement precision
If a driving voltage equal to or greater than the input voltage is applied to the second channel, then the sensitivity of the first channel sensing is enhanced, but the power consumption increases
Solution Approach 1:
The patent changes the voltage parameter of the driving signal applied to the second channel, using a driving voltage equal to or greater than the input voltage to enhance the capacitive coupling effect. This parameter change improves the sensitivity of the first channel sensing by increasing the signal strength, though it does so with increased power consumption as a trade-off
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 approach improves the sensitivity of touch input detection by reducing the influence of offset capacitance, increasing the dynamic range of sensing signals, and allowing for more accurate positioning of touch inputs.
Implementation Method 1
an offset cancellation circuit configured to cancel offset capacitance of a touch screen panel including a first channel and a second channel crossing the first channel
Implementation Method 2
a charge amplifier configured to generate a sensing voltage from a sensing signal output from the touch screen panel, the charge amplifier including an amplifier having a first input terminal connected to the sensing node and a second input terminal to which an input voltage is applied
Implementation Method 3
a capacitive touch sensing device may convert a touch position into an electric signal based on a capacitance formed by a user's hand or an object, such as a touch pen, and a conductive electrode of the capacitive touch sensing device
Data Source
AI summary
A touch screen controller is provided. The touch screen controller includes: an offset cancellation circuit configured to cancel offset capacitance of a touch screen panel including a first channel and a second channel crossing the first channel, the offset cancellation circuit connected to the touch screen panel through a sensing node; a charge amplifier configured to generate a sensing voltage from a sensing signal output from the touch screen panel, the charge amplifier including an amplifier having a first input terminal connected to the sensing node and a second input terminal to which an input voltage is applied; and a channel driver configured to provide a driving voltage, which is equal to or greater than the input voltage, to the second channel in a self capacitance sensing mode for the first channel.