Designing a custom LCD display controller
Editor's Note: When a standard LCD controller is not suitable for a particular display screen or application, OEMs must choose between custom designing their own, or hiring a company that specializes in building custom LCD controllers, such as Digital View. In this article, Digital View explains how to approach a custom LCD controller project, and why even experienced engineers sometimes prefer to outsource these designs.
For more than thirty years, major companies have been making enormous investments into development and manufacturing of advanced LCD panels. The quality, reliability, resolutions and size have continued to increase every year, while the costs have dramatically decreased. All of these issues -- coupled with the benefits of low-power consumption, small physical size and the general "sexiness" of the LCD -- make it very desirable to OEMs and integrators to incorporate into a wide range of products.
All LCD based products, with the exception of some embedded systems, will require a controller to provide a suitable interface and very often a range of display functions critical to a project. As this is a key part of a display system specialist companies have emerged supplying controllers thus providing companies with the opportunity to make or buy, the choice is available. To adequately make this decision, there are quite a number of issues to consider:
Decisions to be made
Among the initial decisions to be made is to define what the controller is expected to accomplish and under what conditions it has to perform - other constraints like the PCB footprint and costs will come later in the project. Some of the primary decisions to be made will include what is the maximum resolution to be displayed and what input interfaces will be needed. The supported input resolution is not necessarily limited to the displayed resolution of the LCD, as current display controllers usually support up-scaling of lower resolution data to match the LCD, and some can even support down-scaling where complex algorithms are used to reduce the resolution of the data to fit the available display format of the LCD. Supported interfaces may cover a wide gamut of choices, including support of industry-standard ARGB interfaces for PC inputs, composite and S-Video connections for low-level video support, higher definition video via analog or digital component interfaces and Digital Video via DVI interfaces.
Fig. 1 shows the major components that comprise the first 80% of the steps involved in a flat panel controller board design.
Selecting a Controller
With some idea of the basic criteria in mind, the next element to be considered is selecting a suitable "engine" to provide the intelligence to accomplish all of these tasks. Controller engines are typically high density single-chip single-purpose devices built by one of a small number of specialized developers. Primary names in the industry include companies like Genesis, Pixelworks and ST Micro. These companies each sell one or more specialized controller chips designed to be the heart of the analog controller design. Controller components vary considerably by features, flexibility, complexity, and of course cost. Considerations in making a selection must include not only reviewing the performance and features of the chip but also looking at the development environment and the support available. Many of the vendors offer a minimal reference design to speed the hardware development and a basic software development toolkit. Development toolkits typically provide basic boot-up code and a utilities package suitable to get a basic display on the screen, but considerable development will be needed to mature this into a complete product with appropriate features and stability. A final consideration here is development support. These components are developed by manufacturers envisioning sales to set-top box manufacturers, high volume desktop monitor manufacturers and the like "so, they may not be too interested in providing support for someone building a few hundred products a year. In some cases, manufacturers impose minimum purchase requirements before any support is available.
With the chosen chip set and a definition of the input ports and desired display resolutions, there is still much more work to be done. Depending on the inputs being supported, the design will need an appropriate analog-to- digital converter with performance appropriate to the application to manage the inbound ARGB signal, DVI receivers and other decoders. Decoders and receivers mean input ports to the controller, and with that come the liabilities of ESD and EMI, plus the necessity of providing protection against the ports being connected incorrectly (over voltage, reverse polarity protection etc.)