An Ultra Low Power Digital to Analog Converter Optimized for Small Format LCD Applications

Liquid crystal displays (LCDs) for mobile applications present a unique design challenge. These small format displays can be found primarily in cell phones and PDAs which are devices that have particularly stringent power requirements. At the same time, the displays are increasing in resolution with every generation. This is creating demand for new LCD display technologies. The predominant amorphous thin film transistor technology is no longer feasible in the new high resolution small format screens due to the fact that the displays require too many connections to the driver and the aperture ratios do not allow high density displays. New technologies such as low temperature polysilicon (LTPS) displays continue to shrink in size and increase in resolution. LTPS technology enables the display manufacturer to create relatively high quality transistors on the glass. This allows for a display architecture which integrates the gate driver on the glass. Newer LTPS LCDs also enable a high level of multiplexing the sources lines on the glass which allows for a much simpler connection to the display driver chip. The electronic drivers for these display applications must adhere to strict power and area budgets. This work describes a low-power, area efficient, scalable, digital-to-analog conversion (DAC) integrated circuit architecture optimized for driving small format LCDs. The display driver is based on a twelve channel, 9-bit DAC driver. This architecture, suitable for % VGA resolution displays, exhibited a 2 MSPS conversion rate, less than 300 pW power dissipation per channel using a 5 V supply, and a die area of 0.042 mm per DAC. A new performance standard is set for DAC display drivers in joules per bit areal density

Thin-Film Transistor Integration for Biomedical Imaging and AMOLED Displays

Thin film transistor (TFT) backplanes are being continuously researched for new applications such as active-matrix organic light emitting diode (AMOLED) displays, sensors, and x-ray imagers. However, the circuits implemented in presently available fabrication technologies including poly silicon (poly-Si), hydrogenated amorphous silicon (a-Si:H), and organic semiconductor, are prone to spatial and/or temporal non-uniformities. While current-programmed active matrix (AM) can tolerate mismatches and non-uniformity caused by aging, the long settling time is a significant limitation. Consequently, acceleration schemes are needed and are proposed to reduce the settling time to 20 µs. This technique is used in the development of a pixel circuit and system for biomedical imager and sensor. Here, a metal-insulator-semiconductor (MIS) capacitor is adopted for adjustment and boost of the circuit gain. Thus, the new pixel architecture supports multi-modality imaging for a wide range of applications with various input signal intensities. Also, for applications with lower current levels, a fast current-mode line driver is developed based on positive feedback which controls the effect of the parasitic capacitance. The measured settling time of a conventional current source is around 2 ms for a 100-nA input current and 200-pF parasitic capacitance whereas it is less than 4 μs for the driver presented here. For displays needed in mobile devices such as cell phones and DVD players, another new driving scheme is devised that provides for a high temporal stability, low-power consumption, high tolerance of temperature variations, and high resolution. The performance of the new driving scheme is demonstrated in a 9-inch fabricated display intended for DVD players. Also, a multi-modal imager pixel circuit is developed using this technique to provide for gain-adjustment capability. Here, the readout operation is not destructive, enabling the use of low-cost readout circuitry and noise reduction techniques. In addition, a highly stable and reliable driving scheme, based on step calibration is introduced for high precision displays and imagers. This scheme takes advantage of the slow aging of the electronics in the backplane to simplify the drive electronics. The other attractive features of this newly developed driving scheme are its simplicity, low-power consumption, and fast programming critical for implementation of large-area and high-resolution active matrix arrays for high precision

Design and characterisation of a ferroelectric liquid crystal over silicon spatial light modulator

Many optical processing systems rely critically on the availability of high performance, electrically-addressed spatial light modulators. Ferroelectric liquid crystal over silicon is an attractive spatial light modulator technology because it combines two well matched technologies. Ferroelectric liquid crystal modulating materials exhibit fast switching times with low operating voltages, while very large scale silicon integrated circuits offer high-frequency, low power operation, and versatile functionality. This thesis describes the design and characterisation of the SBS256 - a general purpose 256 x 256 pixel ferroelectric liquid crystal over silicon spatial light modulator that incorporates a static-RAM latch and an exclusive-OR gate at each pixel. The static-RAM latch provides robust data storage under high read-beam intensities, while the exclusive-OR gate permits the liquid crystal layer to be fully and efficiently charge balanced. The SBS256 spatial light modulator operates in a binary mode. However, many applications, including helmet-mounted displays and optoelectronic implementations of artificial neural networks, require devices with some level of grey-scale capability. The 2 kHz frame rate of the device, permits temporal multiplexing to be used as a means of generating discrete grey-scale in real-time. A second integrated circuit design is also presented. This prototype neuraldetector backplane consists of a 4 x 4 array of optical-in, electronic-out processing units. These can sample the temporally multiplexed grey-scale generated by the SBS256. The neurons implement the post-synaptic summing and thresholding function, and can respond to both positive and negative activations - a requirement of many artificial neural network models

Design of LCOS microdisplay backplanes for projection applications

De evolutie van licht emitterende diodes (LED) heeft ervoor gezorgd dat het op dit moment interessant wordt om deze componenten als lichtbron te gebruiken in projectiesystemen. LED’s hebben belangrijke voordelen vergeleken met klassieke booglampen. Ze zijn compact, ze hebben een veel grotere levensduur en ogenblikkelijke schakeltijden, ze werken op lage spanningen, etc. LED’s zijn smalbandig en kunnen een groterekleurenbereik realiseren. Ze hebben momenteel echter een beperkte helderheid. Naast de lichtbron is het type van de lichtklep ook bepalend voor de kwaliteit van een projectiesysteem. Er bestaan verschillende lichtkleptechnologieën waaronder die van de reflectieve LCOS-panelen. Deze lichtkleppen kunnen zeer hoge resoluties hebben en wordenvaak gebruikt in kwalitatieve, professionele projectiesystemen. LED’s zijn echter totaal verschillend van booglampen. Ze hebben een andere vorm, package, stralingspatroon, aansturing, fysische en thermische eigenschappen, etc. Hoewel er een twintigtal optische architecturen bekend zijn voor reflectieve beeldschermen (met een booglamp als lichtbron), zijn ze niet geschikt voor LED-projectoren en moeten nieuwe optische architecturen en een elektronische aansturing ontwikkeld worden. In dit doctoraat werd er hieromtrent onderzoek gedaan. Er werd uiteindelijk een driekleurenprojector (R, G, B) met een efficiënt LED-belichtingssysteem gebouwd met twee LCOS-lichtkleppen. Deze LEDprojector heeft superieure eigenschappen (zeer lange levensduur, beeldkwaliteit, etc.) en een matige lichtopbrengst

Wide Bandgap Based Devices: Design, Fabrication and Applications, Volume II

Wide bandgap (WBG) semiconductors are becoming a key enabling technology for several strategic fields, including power electronics, illumination, and sensors. This reprint collects the 23 papers covering the full spectrum of the above applications and providing contributions from the on-going research at different levels, from materials to devices and from circuits to systems

NASA Tech Briefs, February 1999

Topics: Test and Measurement; Electronic Components and Circuits; Electronic Systems; Materials; Computer Software; Mechanics; Machinery/Automation; Physical Sciences; Computers and Peripherals

Technology 2004, Vol. 2

Proceedings from symposia of the Technology 2004 Conference, November 8-10, 1994, Washington, DC. Volume 2 features papers on computers and software, virtual reality simulation, environmental technology, video and imaging, medical technology and life sciences, robotics and artificial intelligence, and electronics

NASA Tech Briefs, June 1996

Topics: New Computer Hardware; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery/Automation; Manufacturing/Fabrication; Mathematics and Information Sciences;Books and Reports