Touchscreens in Electronic Devices

Touchscreens have been in continuous widespread use since the PalmPilot. Apple’s Newton was even earlier and if you go back far enough, there were portable computers from Psion that used touch pointing to augment the user interface.

Those early touchscreens required a stylus for input. The overlay over the LCD display was a resistive input device. The current touchscreens have a multi-touch interface that requires a capacitive input matrix.

Image courtesy Aliexpress

Apple certainly did not invent the concept of multi-touch. Microsoft built a prototype platform known as the Surface to demonstrate the human-machine interface possibilities of multi-touch based on the research of Bill Buxton.

Eventually in 2013, Microsoft launched consumer tablet computers to go beyond the original tablet PC form factor brought to market in 2002.

The touch-based interactive system is composed of three main components:

Touchscreen overlay (digitizer),
Touch controller IC,
Touch software and drivers.

The overlay or digitizer is the matrix of input points that can sense human body capacitance. These additional layers are mounted with adhesive directly over the display.

Image Courtesy TI

The output of the digitizer requires some initial processing before the positional information can be handled by the applications processor. This pre-conditioning and analog-to-digital conversion takes place in an integrated circuit known as a touchscreen controller. These are just small microcontrollers customized and pared down for the specific needs of the touchscreen.

Once the screen input location information reaches the applications processor, the driver software takes over to handle the interplay between the user and the operating system and applications.

Although the hardware has been refined over the years, the basics are not that different.

But modern devices like the iPhone and Android-based smartphones enjoy a great deal more market success than their predecessors. As with many of its products, the secret sauce for Apple lies within the software. Touch-based interaction devices were common before the first iPhone launched. However, Apple was able to provide a compelling user experience mostly due to the software and integration into the OS and software applications.