Interconnection
Interfaces and interconnections for displays
Tom Hennessey, business manager for Cable Assemblies at GTK, provides an overview of the evolution of interfaces and interconnections used with display technology
O
ver the last decade there has been an exponential increase in the use of display technology in both
consumer and industrial electronics. Simultaneously there has been a blurring of the technical requirements, with end-users expecting the same performance and usability from industrial products that they enjoy with consumer products such as their smartphones and tablets. Everyone wants everything to be smarter, faster and more compact. These dramatic advancements in display performance have put pressure on the interface between the display and the PCB. As with advancements in other electronic innovations, whilst the choice of cable assembly is integral to the performance of the finished product, it is often overlooked, resulting in a somewhat unwieldy cable solution that takes up more space than anticipated. Here we walk through the different interfaces and the resultant cable assembly options. The original display interface, originating from the 1960s and 1970s was TTL
(Transistor-Transistor Logic). These displays typically used a RGB parallel interface with a minimum of 28 pin connections in the form of an FPC (Flexible Printed Circuit) connected to the panel, and the customer needed to incorporate a ZIF connector on the motherboard. Next came the LVDS (Low voltage
differential signalling) display interface. These run very high speeds on low power using cost-effective twisted pair cables. The transmission distance for LVDS can typically reach 10 metres, which makes it suitable for use in industrial environments where the processor can be located some distance from the display unit. LVDS would now be regarded as a mature technology as it became popular in the 1990s, however it is still a reliable and cost-effective choice for manufacturing environments. The MIPI (Mobile Industry Processor
Interface) interface is born out of the MIPI alliance which has developed a series of interface specifications that are growing in
popularity. The MIPI Display Serial Interface (MIPI DSI) protocol is on track to become the next generation standard for displays and utilises even less power. Displays designed with a MIPI interface will typically have an FPC attached, which needs to be connected to the motherboard.
Larger displays For larger displays, the eDP (Embedded DisplayPort) interface standard was adopted in 2008, with the aim of defining a standardised display panel interface for internal connections. It utilises the same digital signal processing protocol as the DisplayPort standard (its predecessor) but in a smaller connector.
Customising displays Customisation of displays is quite common, and engineers and designers will spend considerable time in selecting the most suitable display for their new product design. This is to ensure it is fit for purpose in the end user environment and that it provides the right user experience in terms of response times, brightness and viewing angles. The display cable, whilst internal and not seen, is also an integral element of the product design and can also be customised by way of length and fold (for FFC/FPC technology) in order for them to
The eDP standard has been through several updates since its inception, with each update resulting in advancements in performance in terms of power saving, extended battery life, and backlight control. eDP cable assemblies are often
manufactured from micro-coax cable and require fewer connections than their LVDS forerunners. They can also incorporate power, data and control signals through one single assembly, making for a more compact design. As an example, where an LVDS cable would typically require 18 signal wires, its eDP equivalent would require only five.
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fit into the product housing. At GTK, our designers support customers with both the selection and specification of the display and the corresponding cable assembly. With early involvement in the design process, we can help to minimise the size and bulk of the cable assembly, along with its final packaging, and we can supply the cables separately or as part of the display sub-assembly. The key to providing the neatest and
most cost-effective solution is considering the cable assembly early in the design process.
gtk.co.uk Components in Electronics June 2019 37
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