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Spectral responses of four light-emitting diodes (LEDs) were investigated because their uses as a photodiode are growing these days. An LED showed reasonable sensitivity to shorter wavelengths which the LED emits. Their spectral response ranges are same or relatively wider than their emission range. In addition, LEDs were used as detectors to analyze test dyes with absorbance measurement technique or with fluorescence measurement technique. Absolute noise level of 0.0001 absorbance unit was observed with the blue LED (nominal λmax = 455 nm) photodiode. Phosphate amount in Kumho River (located in Gyeongsan, South Korea) was determined using IR LED (nominal λmax = 805 nm) as a photosensor. A green LED (nominal λmax = 520 nm) was used to excite rhodamine B (excitation λmax = 560 nm, emission λmax = 575 nm) and red LEDs (nominal λmax = 660 nm) were used to detect fluorescence light emitted from the fluorescence dye. The LOD of rhodamine B was found to be 26 nM with four red LEDs as a photodiode and without using optical filters.

Recently, capacitive sensors, which consist of a sense capacitor and a reference capacitor, have been considered for a sensor array for monitoring biomolecular reactions. Although a capacitance-to-frequency converter (CFC) may be a simple and effective solution for reading a capacitive difference between the sensor capacitors, prior versions lack sufficient accuracy. In this paper, we present a more accurate CFC, which produces a single pulse stream in a wide range of frequencies. This circuit saves residual charges and accumulates them when discharging an integrator capacitor. Implemented in 0.35-μm CMOS technology, our circuit improves the accuracy from about 6% to 0.13 %.

We present a low-complexity interface circuit for capacitive sensors that are integrated into sensor microsystems. To reduce hardware cost while keeping high resolution, a first-order delta-sigma modulator (DSM), which balances the charge from the capacitive difference between sense and reference capacitors with the charge from a fixed-quantity capacitor, is employed. A charge-mode digital-to-analog converter and a successive approximation register are utilized to automatically calibrate the zero point of the interface circuit, which may shift further than a dynamic range. A prototype circuit fabricated in a 0.35-μm CMOS process has an active area of 0.048 mm2. Its DSM operates at a sampling frequency of 1 MS/s with an oversampling ratio of 128. Experiments show that this circuit can read a capacitive difference from -0.5 to +0.5 pF with a 0.49-fF resolution. A capacitive offset that causes the zero point to shift can be canceled in the range from -2 to 2 pF with a 31.25-fF resolution. Measured power consumption was 1.44 mW at a 3.3-V supply.

We propose a high-speed rail-to-rail 10-bit column driver with a reduced die area for LCD-TV applications. This column driver combines an 8-bit resistor-string digital-to-analog converter (R-DAC), constructed using a hybrid-type decoder to reduce the RC time delay and die area, with a 2-bit interpolation DAC. In the output buffer, error amplifiers drive a column line so as to realize a highspeed rail-to-rail drive. Gamma-corrected output voltages are generated by the resistor string of R-DAC, which contains resistors of unequal values that match the inverse of the liquid crystal transmittance-voltage characteristic. A prototype 10- bit LCD column driver was designed and fabricated using a 0.3 mum CMOS technology, and has a settling time of within 2 mus and a quiescent current of 5.4 muA per channel.

We have developed new current demultiplexer TFT circuits for AMOLED and applied the circuits to 2.2-in. QVGA AMOLED. The combination of the current demultiplexer and our voltage boosted current programmed pixel can achieve good uniformity of display image and a compact module.

an emitter and a photodiode. 14 In this report, a pair of LEDs was used to make absorbance measurement. The first LED was a light source as a solid-state light source (i.e. emitter LED) and the other was used as a photodiode (i.e. detector LED). When light illuminates the emitting chip of an LED, small amount of current (~nA level) can be produced. We were using an operational amplifier to amplify photocurrents registered on the detector LED directly. Compared to other light transducers like silicone based photodiodes, a LED is known to be more sensitive to the same wavelength which the LED emits. Bromothymol blue (BTB) was used as a test dye. The red LED’s emission spectra and relative sensitivity in terms of wavelength was also reported here. The test dye’s absorption spectra, linear range of the calibration curve, and limit of detection were also measured. Experimental

We present a capacitance deviation-to-digital converter (CDC) for the thin membrane transducers (TMT) used for bio-molecular detection. Our CDC consists of a capacitance deviation-to-time converter (CTC), time-stretchers, and a time-to-digital converter (TDC). The time-stretchers are innovatively adopted to achieve higher resolution of the CDC with expanse of moderate power consumption. Designed and simulated in 0.35um CMOS bulk technology, the CDC has a resolution of 370aF with a maximum error of 0.027‰, at a rate of 700 samples per second.

A process of making a new type of silicon depth-probe microelectrode array is described using a combination of plasma and wet etch. The plasma etch, which is done using a low temperature oxide (LTO) mask, enables probe thickness to be controlled over a range from 5 to 90 /spl mu/. Bending tests show that the probe's mechanical strength depends largely on shank thickness. More force can he applied to thicker shanks while thinner shanks are more flexible. One can then choose a thickness and corresponding mechanical strength using the process developed. The entire probe shaping process is performed only at low temperature, and thus is consistent with the standard CMOS fabrication. Using the probe in recording from rat's somatosensory cortex, the authors obtained four channel simultaneous recordings which showed clear independence among channels with a signal-to-noise ratio performance comparable with that obtained using other devices.

— To comparatively evaluate various driving methods of an electronic display in respect to image sticking, a consistent and reliable quantification method is required. For proper evaluation, the entire area of a display is often monitored by using a chessboard pattern, and long-range gradual luminous variation in the background is eliminated. Estimation in terms of a single number is also preferred for simple comparison of image sticking. However, the prior method that uses the initial luminance for normalization and estimates the range-to-maximum ratio is not well-suited for the driving methods that relieve image sticking by restoring luminance uniformity. We have developed a method of extracting reference values for normalization and introduced the relative standard deviation (RSD) into our estimation. The resulting method is insensitive to the temporal change in the long-range gradual luminous variation and sufficiently indicative to allow driving methods to be compared effectively. The reference extraction method and the indicative capability of the RSD have been assessed by experiments using a real active-matrix organic light-emitting-diode (AMOLED) display cell.

A new estimation method for image sticking has been developed that can effectively eliminate the influence by the difference in long-range non-uniformity pattern. An 8×8 chessboard pattern was used for selective degradation, and normalization based on extracted reference and coefficient of variation were adopted for better results.

— Early loss of image uniformity has been a critical drawback of active-matrix organic light-emitting-diode (AMOLED) displays operated in time-ratio gray-scale mode. This problem is addressed with an analog calibration technique which measures the voltage across each OLED for a given current and subsequently controls the supply voltage of pixels and the voltage drop across the driving th in-film transistor (TFT) of each OLED. The uniformity of test cells, which were aged to produce image sticking in a chessboard pattern, were improved. A measure of image sticking, called the extracted image-sticking value (EISV), was formulated, which is developed and used for the quantitative evaluation of the calibration method. OLED voltages over a range of about 0.35 V were compensated to produce more uniform OLED currents than those before aging. The variation of luminance associated with image sticking was reduced by about 40% for a full-white image after between 2 and 10 hours of accelerated aging with a constant voltage of 8 V across an OLED.

We propose a new hybrid pixel driving method that combines conventional digital driving with analog compensation for the declining electrical performance that occurs as OLEDs age. Image uniformity, and thus display lifetime, is improved by directly measuring the variation in OLED voltage at each pixel for a given OLED current level and then controlling the voltage drop across its driving TFT of an individual pixel.

Though AMOLED display has been expected as the next generation ideal flat panel display because of its excellent image quality, the AMOLED market has been still limited. This means that AMOLED has not had sufficient competitiveness with LCD yet. There are two critical problems for AMOLED to overcome to compete with LCD. One is Mura problem caused by TFT characteristics deviation in the backplane and the other is short life time of image sticking. In this paper, we will review various approaches to overcome these two critical problems and discuss the practicality of the methods.

An 8-bit coarse digital-to-analog converter (DAC), which adopts both array and tree-type decoders, is combined with a 2-bit fine interpolation DAC to reduce RC time delay and die area of a column driver for LCD-HDTV applications. Error amplifiers drive a pair of column lines in the output buffer to realize rail-to-rail voltage swing with a high slew rate. The design has been fabricated in 0.3 μm LV-HV CMOS technology.