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Advanced Imaging Magazine

Updated: July 8th, 2008 05:26 PM CDT

Understanding the Display Selection Challenge

Selecting Displays
NEC Electronics America
One solution to stable grayscale characteristics, regardless of viewing angle, and an accelerated response time between intermediate grayscales (important in medical imaging) is the super-fine thin-film transistor (SFT) technology offered by NEC Electronics America. SFT induces liquid crystal molecules to line up evenly and rotate horizontally when electrically charged. The rotation angle of the liquid crystal molecules changes according to the amount of electrical voltage applied and affects the amount of light that is transmitted. The liquid crystal molecules are always horizontal, so they appear the same size from the front. Therefore, even if the viewing angle changes, there is very little brightness or color deviation.
NEC Electronics America
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By Robert Dunhouse and Cathy Dotson, NEC Electronics America, Inc.

As the demand for liquid crystal displays spreads to new and different applications, user needs grow more diversified and sophisticated. Each potential market where the LCD plays has its own unique set of needs and requirements. The industrial mobile device market, for example, places size and power consumption constraints on the display, whereas in the test and measurement market, durability is key. Unfortunately, therein lies the problem. With such a diverse set of needs on one hand, and an array of viable LCD products on the other, selecting the appropriate display panel for a specific application can be quite a daunting undertaking.

REFINING THE SELECTION PROCESS

To assist in the process of selecting an appropriate display module for a specific application, a list of key questions can be used to refine the selection process and match the right display to the right market. That list includes questions like:

  • What size (range of size) panel is appropriate for the application?
  • What resolution is required? This is based on the amount or content of information that will be displayed. Examples range from very low-resolution QVGA 320 × 240 to extremely high-resolution QSXGA 2560 × 2048 (5-megapixel) panels.
  • What special optical demands are required (for example, very wide viewing angles, no color shift at extreme viewing angles, low black levels, fast image response, high luminance)?
  • Will the images be used in color or monochrome?
  • What is the panel interface? Several common examples include parallel digital RGB, low-voltage differential signaling (LVDS), transition-minimized differential signaling (TMDS) or analog formats such as composite NTSC and analog RGB.
  • What is the video source (for example, video camera, DVD, embedded video from a single-board computer or a PC with an add-in video graphics card)?
  • What format is the above video source (for example, composite video, analog RGB, parallel digital, LVDS or DVI)?
  • Is the video source format different than the panel's (for example, the customer video source is RGB and the panel interface is LVDS)? If yes, then you must select an interface card to convert the source format to a format compatible with the panel. If no, continue on.
  • Are there special requirements for the backlighting (for example, a low dimming range, wide input voltage range or a small mechanical outline)?
  • In what type of environments will the display be used (for example, high temperature, high humidity, high shock and vibration, direct sunlight)?

While it would be impossible within the confines of this article to examine the display requirements of all possible markets or applications, by keeping the above questions in mind, it is possible to look at a couple of specific market segments in greater detail.

MEDICAL MARKET: HIGH-END MONITOR APPLICATIONS

Displays are used today in a wide range of medical applications, including radiology/mammography, picture archiving and communication systems (PACS), magnetic resonance imaging (MRI) and computed tomography (CT). Here, typical display sizes range from 17 to 21 inches. Each application brings with it a diverse set of display requirements.

For diagnostic applications, medical professionals are now employing LCDs to make more informed, accurate diagnoses using high-resolution displays. For these applications, a high-resolution display, 1 megapixel and above, with precise grayscale characteristics is needed to read MRIs, CT scans, x-rays and mammograms. These displays must feature high luminance, high contrast and a wide viewing angle.

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