Both resistive and capacitive touch screens use indium tin oxide (ITO) sensors, but use them differently. The resistive touch screen uses the mechanical force of the human touch to connect the two flexible layers of the ITO (Figure 1a), and what is a capacitive touch screen controller?
The capacitive touch screen controls the use of: basically, the human being is a moving capacitor. When touching the ITO, the system will change the level of perceived capacitance (Figure 1b).
Capacitive touch screen favored by consumers, there are two main reasons:
1, capacitive touch screen using two layers of TIO, sometimes the use of a layer. It makes use of a texture sensor similar to the checkerboard pattern (Figure 2), so that it can be used to cover the LCD with a whole sheet, which leads to a more clear and transparent screen.
2, due to the capacitive touch screen control using electrolytic capacitor method to detect, the safety glass layer can be placed on the top layer to achieve the seal, which is different from the polyurethane flexible layer resistance screen. It also gives users a more durable design.
Capacitive touch screen design considerations
Capacitive touch screen designers face three major problems: power consumption, noise control and gesture recognition. The latter part of this article will explain to you one by one.
Today's battery powered devices are so many, power consumption is one of the key issues we need to consider. TSC3060 devices such as TI, is designed in accordance with the requirements of low power consumption. Under standard operating conditions, its power consumption is less than 60mA. When the touch behavior is detected, the power consumption can be as low as 11? A. It is at least an order of magnitude lower than its competitors in the same working condition.
Many of the solutions on the market are initially designed for microcontrollers, and then gradually developed into a capacitive touch screen controller. At the beginning of the design of capacitive touch screen controller devices, there is no need to consume additional current and clock cycle of excess hardware. Most systems have a central processor that can be a digital signal processor, microprocessor or microcontroller unit (MCU). So why do you want to add an engine to a system that has been properly adjusted? TSC3060 is a special design without a microcontroller.
If the controller is unable to distinguish between actual touch and potential interference sources, not to mention the use of ultra long battery life. The main noise source of the touch screen usually comes from LCD, which ultimately depends on the tradeoff between quality and cost. AC common ground LCD is usually cheaper, but the noise level is higher. DC common ground LCD has DC shield that can reduce noise, but will increase costs.
A typical way to help reduce the number of perceived noise in the ITO sensor and the touch screen controller is to maintain a certain air gap between LCD and ITO. This allows for a certain distance between the two, thereby reducing mutual interference. Another way to deal with noise is to use filters. For example, the TSC3060 contains a programmable mixed signal filter that can be used to reduce noise. These filters are integrated into the hardware via an integrated MCU. This means that they are near to complete the task faster than the use of software filters. The fast response to the actual touch coordinates can also reduce the total system resource consumption.
The last design problem is gesture recognition. Gestures are not necessarily large and complex. Gestures can be a simple finger slip. System host MCU can easily identify a number of simple gestures, such as: pinch, pull, zoom, rotate and double-click and three combos, etc., and can be "internal" processing. Adding a dedicated engine may reduce the processing load of a little bit of MCU bandwidth, but increase the power consumption. In addition, the dedicated engine used to complete the proprietary algorithm gesture recognition, the designer can not see. TSC3060 and other devices to the work of the system has been pushed to the main processor, so that the majority of designers can freely develop their own royalty free algorithm.
Now you know what a capacitive touch screen controller is.