Originally Published MEM Fall 2001
DISPLAY TECHNOLOGIES
Current Trends in Active-Matrix Liquid-Crystal Displays
Mark Kearns, marketing director of medical business, Planar Systems
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An
AMLCD can display data from multiple devices without consuming valuable
space.
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With their high resolution, bright and clear colors, and fast video-response times, traditional cathode-ray tube (CRT) monitors have long had a place alongside medical equipment. However, the lead that CRTs have been enjoying is beginning to narrow.
Anyone who has recently been in a hospital or other healthcare environment would have likely noticed two things: the decrease in the size of the rooms and the increase in the number of devices in these rooms. Because of this combination, flat-panel displays such as AMLCDs have an immediate advantage. When used as stand-alone monitors, these thin, lightweight displays can be up to 75% smaller than CRT monitors. The size, weight, and power-consumption advantages of flat-panel displays compared with traditional CRTs are particularly important in space-constrained patient-care areas. In these areas, monitors are often mounted on articulated arms that swing out from the wall.
Due to the depth and weight of CRTs, this poses potential safety hazards to personnel moving quickly about the room. In comparison, flat-panel displays can mount almost flush to the wall, and can easily swing out for ease of viewing and back out of the way for mobility and safety. Desk and counter space in nursing stations and treatment areas is also optimized by using flat-panel monitors.
Flat-panel displays require significantly less power and generate fewer emissions and less heat than CRTs. The power required for a 17-in. CRT monitor is typically 100 W, whereas the power required for a 15-in. AMLCD monitor is 40 W. The standby power required for a 17-in. CRT is 10 to 15 W, whereas the standby power for a 15-in. AMLCD is 5 W. A 17-in. CRT is compared with a 15-in. flat-panel monitor because the viewable area of a 15-in. flat-panel monitor closely approximates that of a 17-in. CRT monitor. In many cases, the demand for a flat-panel monitor is simply market driven: Customers want the thinner, lighter, and sleeker look of the AMLCD monitor as opposed to a bulky CRT.
In addition, AMLCD technology is rapidly closing the performance gap. Although CRTs still provide higher resolution than AMLCDs, the color, image quality, and video-response rate of AMLCDs are as good as that of a CRT for almost any medical use and at any resolution. AMLCD screen sizes continue to increase to meet medical industry requirements, and the cost of these monitors continues to drop as economies of scale are reached through the rapid growth of commercial desktop flat-panel monitor usage.
Convergence in Device Functionality
A recent trend in the design and use of medical equipment is the union of multiple devices in a single machine. At the same time, strategic partnerships are being forged among medical equipment manufacturers who are finding that a single display can often meet the needs of multiple pieces of related equipment, while offering the caregiver a single point of reference. Healthcare providers can now receive richer content, using large, high-resolution color monitors that can display parameters and diagnostic information from multiple devices, while viewing only one screen to see all pertinent data.
For example, a manufacturer of a monitoring device may have historically displayed waveforms and data on a medium-resolution display integrated into the device. By partnering with other equipment companies that manufacture devices for the same critical-care arena, the manufacturer may provide a more cost-effective module containing only the sensors, monitoring, and analysis tools but without an embedded display. Instead, a single 15-in. color, flat-panel monitor could be used to display both the monitoring data generated by the module along with the data from other related devices used in the operating room or intensive care center.
This convergence to a stand-alone display from multiple embedded displays allows equipment manufacturers to focus on their core competencies while reducing or eliminating display-related design costs, reliability issues, power requirements, and emissions concerns. By moving to a stand-alone medical display, the manufacturer is also ensured that the display meets regulatory standards such as UL 2601 and IEC 60601.
With convergence comes a greater information need, so a large screen size is generally required to display a variety of parameters and types of diagnostic information that can be read from a distance and at varying viewing angles. AMLCD technology is advancing to support larger screen sizes ranging from 15 to 21 in., and flat-panel displays provide more viewing area per dollar than a comparable CRT. AMLCDs provide high-resolution color up to an ultraextended graphics array level (1600 x 1200 pixels and 16.8 million colors), which provides quick differentiation between discrete pieces of information displayed. AMLCDs offer a wide viewing angle (160°) and at-a-glance readability (300:1 contrast ratio), which is crucial in critical-care applications, where decreasing the time required to read, interpret, and act on information can save lives.
In addition to the benefits to the caregiver, a stand-alone, medically certified display can reduce equipment manufacturers' certification efforts during rapid display-technology changes. A medically certified flat-panel monitor meets UL 2601-1 and IEC 60601-1 requirements for ultralow current leakage and electromagnetic interference, in addition to a host of features ensuring electrical and physical integrity. Medically certified monitors can provide automatic brightness adjustments, contrast adjustments, built-in touch screen controls, and more.
The challenge in
medical environments is to find room for more diagnostic and monitoring equipment
even as space becomes more limited. With advances in AMLCD technology, and the
corresponding advances in the integration into plug-and-play monitors, medically
certified versions of these new liquid-crystal displays are rapidly taking the
place of traditional CRTs and embedded flat-panel displays in the medical equipment
marketplace.
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AMLCD Technology For displays of high information content, the viewing-angle and contrast problems of highly multiplexed passive liquid-crystal displays would disappear if each element were directly addressable. Because of geometry and space limitations, this cannot be accomplished through electrode design. The active-matrix approach addresses this problem by incorporating a switch at each picture element or pixel. An AMLCD is constructed using thin-film transistor technology by building a grid of switching elements on the inside surface of the glass substrate (see Figure 4). The switching elements may be two-terminal devices, such as diodes, or three-terminal devices, such as transistors. Each display pixel has a switch located at the pixel. The switches are arranged in rows and columns, with the gates of each switch of one row tied together for connection to an external voltage source. The sources of each column of switches are also tied together for external addressing. When voltage is applied to a row of the matrix, the gates of that row allow data to be entered at the sources. The voltage at the source either turns the elements on or not. The voltage is then removed from that row, closing those switches, and the next row is addressed. This cycle is applied to each row of the matrix, then the cycle repeats itself, starting with the first row. Each pixel, therefore, is individually addressed. The advantage to this method is that maximum contrast is achieved for the liquid-crystal material. Pixels that are turned on will twist the polarized light entering the cell from the backlight through the rear polarizer, allowing it to pass through a color filter and the front polarizer. Pixels that are turned off will not allow the polarized light entering the rear of the cell to pass through the front polarizer, creating a dark element. The amount of light passing through the cell can be controlled by the switching element, allowing various shades of the three basic colors to be created, to as many as 16.8 million colors. |
Copyright © 2001 Medical Electronics Manufacturing
