Capacitive touch screen design considerations
Capacitive touch screen designers face three major problems: power consumption, noise control and gesture recognition.The rest of this article will walk you through each one.
With so many battery-powered devices available today, power consumption is one of the key system issues we need to consider.Devices such as TI TSC3060 are designed for low power consumption.Under standard operating conditions, its power consumption is less than 60mA.Its power consumption can be as low as 11 A for touch detection.It is at least an order of magnitude lower than its competitors at the same operating condition.
Many of the solutions on the market started out as microcontrollers and evolved into capacitive touch screen controllers.Designed from the start as capacitive touch screen controllers, there is no excess hardware that consumes extra current and clock cycles.Most systems already have a master processor, which can be a digital signal processor, microprocessor, or microcontroller unit (MCU).So why add another engine to an already fine-tuned system?The TSC3060 is designed specifically for use without a microcontroller.
Not to mention long battery life if the controller can't tell the difference between actual touches and potential sources of interference.The main source of noise on touch screens is usually LCD, which ultimately depends on the tradeoff between quality and cost.AC public grounded LCDS are generally cheaper but have higher noise levels.DC grounded LCD has DC shield, can reduce noise, but will increase the cost.
A typical way to help reduce the amount of noise that ITO sensors and touch-screen controllers can perceive is to maintain a certain air gap between the LCD and the ITO.In this way, a certain space can be set apart between the two, so as to reduce 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 installed into the hardware via an integrated MCU.That means they can perform tasks closer to home faster than they can with a software filter.Quick response to actual touch coordinates also reduces total system resource consumption.
The latter design problem is gesture recognition.Gestures are not necessarily large, complex waves.Gestures can be as simple as a single finger swipe.System host MCU can easily recognize some simple gestures, such as: pinch, pull, zoom, rotation and double-click and triple tap, and can be "internal" processing.Adding a dedicated engine may reduce the system MCU bandwidth processing load a little, but it increases the power consumption.In addition, proprietary algorithms for gesture recognition are not visible to the designer.TSC3060 and other devices push this work to the existing main processor in the system, so that the majority of designers can freely develop their own version of tax-free algorithm.
This paper compares the functions and advantages of the resistive and capacitive touch screen controllers and explains the reasons for the increasing popularity of the latter.The paper also introduces three main considerations in designing the touch screen controller, namely power consumption, noise control and gesture recognition, and gives some possible solutions