The digitizer (also known as the touchscreen or glass lens) is the medium through which we communicate with our touchscreen devices. Embedded in this seemingly straightforward lens are several layers of sophisticated materials: above the central glass substrate are a series of thin, conductive components; below are a stack of LCD display layers.
How do digitizers work?
Broadly speaking, digitizers work by converting analog signals to digital ones; touch screen digitizers recognize changes in their surface conditions, which, depending on the device, can include changes in light, pressure, or electrical current. When you touch the screen of an iPhone, for example, your finger alters the electrical current of the digitizer, and the device recognizes that change, activating its software accordingly.
Obviously, the changes detected through the digitizer are often quite subtle; for a device like the iPhone 4, minor differences in the placement and movement of two fingers correlate to a significantly different software response. The detection process also has to be fast; within a fraction of a second, the device has to read the change in its surface, make an educated guess as to the intended point of contact, and respond accordingly.