Feature: Industrial electronics
ASICs: Providing resolution to industrial touchscreens
By Ross Turnbull, director of business development and product engineering, Swindon Silicon Systems
T
hanks to today’s touch- screen technology, interaction with a computer can be as instinctive as a conversation between
two humans. Ross Turnbull, director of business development and product engineering at Swindon Silicon Systems ASIC design and supply company Swindon Silicon Systems, discusses how Application Specific Integrated Circuits (ASICs) play an integral role in uniting man and machine. Touchscreens now feature extensively
in our daily lives, not least within our mobile devices, but also in retail, healthcare and industrial settings. More niche applications call for specialised touchscreens that are sufficiently sensitive to detect a human finger through thick glass, through gloves, or even at a distance above the screen’s surface.
Electronic challenges Almost all modern touchscreens use the ‘projected capacitance’ technique, where a matrix of invisible conductors is embedded within the display. At each crossing point, the conductors form coupling capacitances between one another, at least partially through the air above the display. A finger in close proximity reduces
this coupling, albeit by a tiny fraction. Te job of the touchscreen controller is to measure the numerous capacitances, usually by driving each wire in turn with a voltage stimulus and thus pushing small currents through them. By measuring the many tiny currents simultaneously, it is possible to perceive the effect of any touches and calculate where they occur. Upon entering the controller, each
wire’s signal is first passed through filtering components to reject interference. Te signal is then amplified and sampled before being digitised by
10 September 2024
www.electronicsworld.co.uk
an analogue-to-digital converter (ADC). Te replication of all this componentry, to serve the numerous wires in the panel, represents a significant challenge to the cost and form factor of the electronics. Because the changes in capacitance are
so subtle, great attention must be paid to noise when designing the controller. Furthermore, the many channels must operate at high frequency in order to win an acceptable ‘frame rate’ from the touch panel. Matching between the channels must be good in order to simplify subsequent processing, calling for tight control over circuit properties and stray capacitances.
The application of ASICs to these challenges When such systems are initially prototyped, these electronic functions are provided by a multitude of off-the-shelf integrated circuits (ICs) supported by an array of capacitors and resistors. Tis is
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