Anand Lal Shimpi, Brian Klug & Vivek Gowri, AnandTech:

Touch sens­ing has to be time mul­ti­plexed with dis­play dri­ving oth­er­wise the touch sig­nal might be entirely lost in noise. At the same time, touch sens­ing is often around dou­ble the fre­quency (120–175 Hz) of dis­play draw­ing (60 Hz), so this has to be done care­fully dur­ing quiet peri­ods, and thus that required com­mu­ni­ca­tion and inte­gra­tion. The iPhone 5 uses a com­bi­na­tion of TI and Broadcom con­trollers to do dis­play con­troller and touch sens­ing, where pre­vi­ous gen­er­a­tions of iPhone sim­ply just used a sin­gle chip TI solu­tion. In future gen­er­a­tions this will come back down to just being a single-chip solution.

A single-chip that acts as both dis­play con­troller and touch sens­ing sounds good. Thanks to in-cell touch tech­nol­ogy, the def­i­n­i­tion of mobile dis­play will change soon in the future: A mobile dis­play will mean a dis­play capa­ble of respond­ing to touch.

[...] ITO traces are only laid down where they need to be on top of and below the glass sub­strate (for both trans­mit and receive lay­ers of the dig­i­tizer), and the areas inbe­tween those traces are then filled with an index-matching space fill mate­r­ial to dimin­ish their vis­i­bil­ity. How well this space fill is done and how close the index is to ITO’s is one of the qual­ity met­rics of a dig­i­tizer to begin with, and often these rows and columns are vis­i­ble under direct illu­mi­na­tion either out­doors or with good eyes indoors.

This is an impor­tant obser­va­tion. In-cell touch com­pletely elim­i­nates these vis­i­ble traces of ITO in the touch layer, because the touch layer is no more. Now the only thing to get rid of is the cover glass.