Kunlun Tongtai touch screen - the design points of capacitive touch screen

Accuracy: Accuracy can be defined as the maximum positioning error in a predefined touchscreen area, measured in the straight-line distance between the actual position of the finger and the measured position. When measuring accuracy, a simulated or mechanical finger is used. Place your finger in an exact position on the panel and compare your actual position with the measured position. Accuracy is very important, and users expect the system to accurately find the position of their fingers. One of the most criticized drawbacks of resistive touchscreens is their low accuracy, which wanes over time. The precision of capacitive touchscreens has created many new applications, such as virtual keyboards and handwriting recognition without a stylus.

Finger spacing: Finger spacing is defined as the shortest distance on the screen between the center points of the two fingers as the touchscreen controller measures the position of the two fingers. Place two analog or mechanical fingers on the panel and gradually close the distance between the two fingers until the system detects that both fingers are one finger. Some touchscreen vendors refer to the distance between the edges and edges, while others refer to the distance between the center points. The 10 mm finger spacing of a 10 mm mechanical finger indicates that multiple fingers are touching the screen, or that the distance between the fingers is 10 mm, depending on the specification of the touch controller. Without good finger spacing, you can't design a multi-touch solution. Finger spacing is especially important for emulated keyboards, as finger spacing on the screen is usually very short when using emulated keyboards.

Response time: Response time is defined as the time between a finger touch event on the touchscreen and an interrupt signal generated by the touchscreen controller. The measurement method is to electronically touch the environment of a finger touch screen, or to move an analog finger on a panel. Response time is especially important because it directly affects how quickly a user can move their finger across the screen; pan or flick the action; Write on the screen with your finger or pen. Slow response times on the touch panel may result in short pauses and no movement detection. The response time of the touch screen is a part of the system response time, which includes:

· X/Y Axial Scanning: The time it takes for a touch controller to scan and measure the change in capacitance on a sensor.

· Finger Detection: Compares panel capacitance changes to predefined finger defaults. If the change exceeds the default value of the finger, the touch of the finger will be detected.

· Finger position: Calculate the actual position of the finger based on the result data obtained by multiple sensors.

· Finger tracking: When there are multiple fingers on the sensor, each finger must be correctly identified and assigned a unique identification symbol.

· Interrupt Delay: Refers to the delay between the master and the service, which in most systems does not exceed 100 microseconds.

· Communication: Generally, the system uses I2C at 400kHz or SPI at 1MHZ to communicate with the master.

There are many tools on the market that can be used to shorten the response time, but the key lies in the intelligence of the touch chip, such as the more creative way to detect the position of the finger by scanning only part of the screen, and when the finger is detected, it can quickly scan and calculate the actual location of the finger, so as to save power and time. Another important tool is parallel processing, which uses different hardware components for scanning, finger processing, and communication, so that all work is synchronized. Highly optimized algorithms for finger detection, finger positioning, and finger identification (ID) reduce processing and response times.

Picture update rate: The time between two adjacent frames of touchscreen data within a data buffer when a finger appears on the touchscreen. A low screen update rate will cause the system to detect a pause in the action, and the detected movement path will become a discontinuous line segment instead of a smooth curve. In other words, a touch panel with a high screen update rate can provide more data points that can be translated into smooth or complete shapes or movements, and a high screen update rate can also improve the interpretation of gestures. Smart touchscreen controllers such as TrueTouch are able to adjust their screen update rate to match system requirements. Hand-drawn or handwritten apps require a fairly high screen update rate, but the phone's dialpad only needs to cut off the main control when the user presses or releases a button.

Average power consumption: refers to the average power consumption of the touch system, including the time when the controller IC is working, such as scanning, processing, communication, sleep, etc., and the time when the main processor receives and interprets touch data.

Power consumption is a very common performance parameter: the current consumed by the measuring device is multiplied by the voltage to calculate the power consumption. In terms of power consumption of touch panels, more precise formulas are needed because different usage patterns will generate different power consumption. The standby time of the phone depends on the current consumed by the touchscreen in standby or sleep mode.

When the touch screen is working, it is also divided into many modes, such as Touch Wake (WOT) and Cheek Detect, such as answering a 5-minute call, when viewing or entering a phone number, the phone may switch to touch mode for 10 seconds, and then switch to WOT or cheek detection mode when reminding the call. Even when sending text messages (SMS), the hybrid WOT mode is in contact with the actual finger, and the controller IC switches between various sleep modes when keystrokes are pressed or thinking.

Without these power consumption modes, it's easy to be misled by the system's power consumption, and in most cases, the touchscreen switches to cheek detection mode and touch wake mode 90-99% of the time. Some systems allow the user to set the ratio of processing time to sleep mode, even while the finger is still on the panel. If the system only detects that the finger is placed in the same position, it does not need a 200MHz image update rate. To develop a high-performance touchscreen, it was necessary to use a low-power system with a sleep mode and an innovative sleep and wake mode.

Kunlun Tongtai touch screen - the design points of capacitive touch screen

Kunlun Tongtai touch screen - the design points of capacitive touch screen

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