James Lawrence Sanford

4.2: TFT AMOLED Pixel Circuits and Driving Methods

Active matrix organic light emitting diode AMOLED displays are now entering the market place. TFT active matrix allow OLED displays to be larger in size, higher in resolution and lower in power dissipation than is possible using a passive matrix. A number of TFT active matrix pixel circuits have been developed for luminance control while correcting for TFT parameter variations. The circuits and driving methods are reviewed. A new driving method is presented

IBM's Linux watch, the challenge of miniaturization

Nearly four years in development, the IBM Linux watch contains a complete computer system that runs Linux, displays X11 graphics, and has wireless connectivity. The system fits in a case that could pass as a slightly unusual analog timepiece with a somewhat odd shape and an extraordinarily brilliant face. The developers have created two versions of the watch, one with an organic light-emitting diode display and the other with a liquid crystal display. Still considered a research prototype, the watch already runs some personal information management applications, and it can communicate with PCs, PDAs, and other wireless-enabled devices, viewing condensed e-mail and directly receiving pager-like messages. Eventually, users will be able to access various Internet-based services, such as up-to-the-minute information about weather, traffic conditions, the stock market, and sports.

A one-megapixel reflective spatial light modulator system for holographic storage

A prototype reflective spatial light modulator (SLM) system has been developed for writing megabit pages of data into a holographic medium at a rate of 12 pages per minute. The SLM is based upon a crystalline-silicon reflective active-matrix array with integrated data drivers, using liquid crystal (LC) electrooptics and a personal computer system with an interface to provide data. The LC has been optimized for high contrast and efficiency with coherent illumination. The resolution-limited contrast was measured at 4:1, which was high enough to provide bit-error-free charge-coupled-device images using modulation and error-correction codes.

Design and fabrication of a prototype projection data monitor with high information content

A prototype 28-in.-diagonal desktop data monitor capable of displaying 2048 × 2048- pixel images has been designed, built, and evaluated. The monitor uses optical projection technology. A reflective, crystalline silicon active-matrix light valve using liquid crystal electro-optics and a digital electronic interface architecture is described. This rear-projection monitor has four million resolvable pixels, uses three light valves to achieve color, has a low-gain surface diffuser screen, and functions as a fully interactive, color personal computer monitor with motion video capability. The monitor is 20 in. deep.

Silicon light-valve array chip for high-resolution reflective liquid crystal projection displays

A crystalline silicon active-matrix 2048 × 2048- pixel light-valve array chip has been designed and fabricated as part of the development of a reflective liquid crystal technology for projection displays. The small feature processing and higher circuit performance available with crystalline silicon technology were exploited for the design and fabrication of the active-matrix chip. A 10-V CMOS process was developed to satisfy active-matrix pixel-cell requirements. Row-selection circuits were integrated which incorporate redundant data paths. Adjacent-line demultiplexing circuitry was integrated to minimize the number of external data drivers, to minimize the number of connections, and to maximize chip yield. The pixel, row-driver, and data-driver demultiplexing circuit designs and performance are discussed. The testing methods are presented, The chip is 64 mm on a side and is used in a prototype rear-projection color display system. Companion papers describe the system and its additional components incorporated in the prototype display system.

24.2 Direct View Active Matrix VGA OLED-on-Crystalline-Silicon Display

This paper describes the pixel and array circuitry, which includes a CMOS SRAM cell and a precision current source at each pixel, of a direct view VGA active matrix OLED-on-crystalline-silicon display, developed jointly by IBM Research Division and eMagin Corporation. The display has applications for low-power personal information appliances such as a computer wristwatch. The display obtains data and control signals directly from the memory bus of the appliances processor.

Vt Compensated voltage‐data a‐Si TFT AMOLED pixel circuits

Active-matrix organic light-emitting-diode (AMOLED) displays are now entering the marketplace. The use of a thin-film-transistor (TFT) active matrix allows OLED displays to be larger in size, higher in resolutions and lower in power dissipation than is possible using a conventional passive matrix. A number of TFT active-matrix pixel circuits have been developed for luminance control, while correcting for initial and electrically stressed TFT parameter variations. Previous circuits and driving methods are reviewed. A new driving method is presented in which the threshold-voltage (v t ) compensation performance, along with various circuit improvements for amorphous-silicon (a-Si) TFT pixel circuits using voltage data, are discussed. This new driving method along with various circuit improvements is demonstrated in a state-of-the-art 20-in. a-Si TFT AMOLED HDTV.

An SXGA reflective liquid crystal projection light valve incorporating inversion by pixel bootstrapping

A new experimental SXGA liquid-crystal-on-silicon reflective projection light valve is described. It incorporates a novel inversion scheme, the bootstrapped pixel method, which extends the available pixel voltage range with lower applied voltages from the external data driver. This can enable the use of liquid crystal modes and performance-enhancing pixel structures which increase the pixel voltage requirement without incurring the additional cost of higher-voltage technology in the light-valve chip or the data driver. Alternatively, with present liquid crystal modes and pixel structures, it can permit the use of a denser, lower-voltage silicon process permitting more function on a chip or smaller, less expensive chips. Using the new light valve, the pixels were operated at 12 V peak-to-peak, the technology maximum, with no voltages in the device above 12 V and a data-line voltage range of 6 V. The new method introduces no new image artifacts.

Technology and design of an active-matrix OLED on crystalline silicon direct-view display for a wristwatch computer

The IBM Research Division and eMagin Corp. jointly have developed a low-power VGA direct view active matrix OLED display, fabricated on a crystalline silicon CMOS chip. The display is incorporated in IBM prototype wristwatch computers running the Linus operating system. IBM designed the silicon chip and eMagin developed the organic stack and performed the back-end-of line processing and packaging. Each pixel is driven by a constant current source controlled by a CMOS RAM cell, and the display receives its data from the processor memory bus. This paper describes the OLED technology and packaging, and outlines the design of the pixel and display electronics and the processor interface. Experimental results are presented.

A high-resolution and high-speed ferroelectric liquid-crystal shutter array print head

A 1-in-wide, 577-dot/in, and 4:1 multiplex ferroelectric-liquid-crystal (FLC) shutter array has been fabricated and tested for optical performance. The array has a cell gap of 2.8 mu m and is surface stabilized with an FLC material of high spontaneous polarization (140 nC/cm/sup 2/) and fast switching time (16 mu s) at room temperature. It is capable of operating at a speed of 6.5 in/s (24 p.p.m. printing speed) with optical contrast ratios of better than 4. Using tungsten-halogen illumination, a prototype print head has been made, and print samples have been obtained on an electrophotographic printer engine. >