Semicustom TFT displays: size (and shape) is everything

Mike Logan
Display and Input Technology Manager
TFT letterbox display
Display designers should seek out solutions like this letterbox type display rather than be constrained by the standard display form factors

A glance at the catalogues of the major industrial LCD display manufacturers and you will notice a strange similarity – the majority of TFT displays are in a relatively small range of standard sizes, and almost all are in 3:4 or 16:9 aspect ratios.

Who decides standard LCD display size?

These sizes have everything to do with the convenience of the display manufacturer and little or nothing to do with the needs of your project. If you end up increasing your case size to accommodate a larger display, there is a cost to that. A bigger display will use more power too, which can be an issue.

Alternatively, you may go for a display that is too small and present less information on the screen or use a smaller type size than you’d ideally like. There is a cost to that too. There is actually no need to be constrained by the relatively limited catalogue options that the major display manufacturers offer. Start from a blank piece of paper and decide what size you’d really like – if you choose the right supplier you will able to achieve the exact size you require at the right price.

What about the TFT display shape?

There is also no good reason why a display needs to be in 3:4 or 16:9 aspect ratio. They have become the industry standard by default, but there are a great many applications where a standard TFT won’t fit. For example, in rack mounted equipment there are height restrictions. If you’re trying to build a module of 1U or 2U that limits the height of display – which limits the width too due to the restricted range on offer. You’re therefore left with the clumsy alternatives of fitting several smaller displays side by side, or squeezing the information you want to present on a smaller display than necessary. Many customers end up sticking with a mono character unit just because they are offered in a wider range of sizes.

There is a middle way between a full custom display and the limitations of a catalogue product – and that is a semi-custom display. Customers can have these displays cut to their specified height, and add touch control, FPCs and a backlight as needed. The initial NRE (non-recurring engineering) cost is less than one-tenth the normal upfront charge – which is usually much cheaper than redesigning the case to accommodate a larger display.

Semicustom LCD colour displays

Since its launch on the smallest display sizes, our semi-custom service has been hugely popular, allowing many customers to transform their system with a colour display instead of a mono character unit.

Though at first glance a standard product can look cheap, most of the time a semi-custom display is the best option. Manufacturers that have an extensive catalogue of display options usually build their standard display range to order anyway – so there are no actual economies of scale. Some manufacturers will produce a limited range of displays in high volume – but if you specify these you are placing yourself in your suppliers’ hands. If the display market changes and the demand shifts to different sizes, they will discontinue models in a heartbeat leaving industrial customers high and dry.

With a semi-custom solution, it is possible to reduce the cost by removing unwanted elements. You can choose how many backlight LEDs you need – saving cost and reducing power. You can specify a simpler and cheaper graphics IC, add or remove performance enhancement films etc. to create a screen that delivers exactly what your application requires – no more and no less. A very cost effective way of creating a non-standard size and shape like a letterbox format, is to cut an LCD display to size. This can give you the exact size you need without the NRE and high MOQ of a creating a custom display.

So, my first piece of advice to the display specifier is not so much dream big, as to be demanding. Figure out the size that works for your system, then find a supplier that offers the flexibility and will deliver what you need. 

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