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To optimize the performance of organic light-emission devices (OLEDs), optical simulation or electrical simulation is often used to help designing the device structures. However, employing electrical or optical simulation separately to optimize the device might lead to incorrect conclusions. A few researches have combined optical and electrical simulations to design OLED structures by merely inserting the maximum carrier recombination rate calculated from electrical simulation into optical simulation programs, which is still insufficient for optimization of OLEDs due to lack of considering the influence of optical interference positions. In this paper, we investigate the OLED performance by using three simulation methods, pure optical, pure electrical, or combination of both, to design the devices. Using the models incorporating both electrical and optical simulations, we found that the optimal emission position occurs neither at the place with the best optical interference nor at the point where carrier recombination rate is the maximum. In order to verify the simulation results, we design the testing devices, red fluorescence OLEDs of bi-layer structures, with various positions of recombination emission. It is found that the position of recombination emission has major impact on the device performance of OLEDs, which lead to some important design rules. With integration of electrical and optical simulations, the real emission position could be predicted with excellent agreements to the experimental results. Applying this method to design the red fluorescent bi-layer OLEDs, the device with very high efficiency of 8.44 cd/A was achieved.

PurposeThis paper aims to solve the typical thermal airflow sensor's high power consumption and integration difficulties, based on the FS5 thermal element and constant temperature measurement method, a flow sensor is developed with high measurement accuracy, low power consumption, small size, low cost and easy system integration.Design/methodology/approachA small wind tunnel was used to test and assess the sensor's measurement range, reaction time, stability, repeatability, measurement accuracy and multi-temperature calibration was performed in the temperature range of −10°C to 30°C. The effect of ambient temperature on the sensor's measurement data is investigated, and the coefficient correction method of power function was investigated to implement the sensor's software temperature compensation function.FindingsThe results show that the sensor is stable and repeatable, the output voltage has a power function relationship with the airflow rate, the flow rate measurement range is 0–18 m/s, the response time is less than 3 s, the measurement accuracy at high flow rates is within 0.4 m/s and the temperature-corrected airflow rate measurement error is less than 5%. Setting the temperature calibration interval to 2°C and 5°C has the same temperature compensation effect, reducing the sensor's calibration effort significantly.Originality/valueThis paper demonstrates that a thermostatic method is used to construct a thermal wind speed sensor that delivers accurate measurements in the wind speed measuring range of 0–18 m/s under test conditions. In addition, the sensor's performance is evaluated, and calibration tests for a wide range of temperatures are done. Finally, based on the power function correction method, a temperature compensation algorithm is proposed.

Graphene is different from most optical materials in that it is a thin material layer with a thickness as small as one atom. Graphene layers can be incorporated into optical simulations using either a surface conductivity material model or a volumetric permittivity material model; however, introducing graphene through a volumetric permittivity is computationally inefficient because it requires very fine discretization grids. We have recently developed a more efficient approach that enables the use of comparatively coarse grids by formulating a discretization of Maxwell’s equations (in the time or frequency domains) that combines a surface conductivity description of graphene layers with a volumetric permittivity description of other optical materials. This approach includes the full dispersion characteristics of graphene as specified by the Kubo formula. This paper demonstrates how the combined material description approach can be used to efficiently model state-of-the-art devices that take advantage of the energy confinement provided by surface plasmons. We show how to efficiently model TE and TM polarized surface plasmons, a surface plasmon waveguide switch, and an electro-optical modulator. This last example also includes electrical simulations of graphene and demonstrates how both optical and electrical simulations can be combined to produce a complete model of a graphene based device. For each example, we compare with previously published results, including experimental results.

The avalanche photodiode is designed by using SILVACO TCAD tool, a simulation tool for fabrication process and also electrical performances. This project proposed a planar Si Avalanche Photodiode with presence of guard ring and non guard ring. It is operated in reverse bias which means by using Silvaco Athena and Atlas, the anode connected to the negative terminal and ground to the cathode in fabrication. The project includes the effect and relationship of avalanche photodiode between substrate concentrations and doping, type of materials, with the breakdown voltage and leakage current were investigated. Then, the structure is applied with guard ring structure .At the end, we choose the best optimized design of avalanche photodiode based on current-voltage characteristics.

A single component, visible wavelength, heterodyne laser Doppler anemometer was constructed based on solid-state laser diode technology for use in fluid dynamic research. With the recent advancements in solid-state laser diodes and solid-state avalanche photodiodes, it is possible to construct miniature laser Doppler anemometer systems solely employing solid-state technology. Such systems have the advantages of small size, light weight, low-power consumption, low cost, and ruggedness. The subject of the current research was to quantitatively evaluate a miniaturized laser Doppler anemometer system constructed with visible laser diodes and an avalanche photodiode detector. Evaluation measurements in a turbulent, stagnating jet are presented and compared to both hot-wire and five-hole probe data. The miniature solid-state laser Doppler anemometer system was found to agree within 2% for mean velocities and agree within 5-20% for root mean square turbulent velocities.

Geometry dependence of the light collection efficiency of BGO crystal scintillators read out by avalanche photo diodes

Development of high performance Avalanche Photodiodes and dedicated analog systems for HXI/SGD detectors onboard the Astro-H mission

When designing analog circuits, performance stability is an essential aspect, especially against temperature variations. The reference current, which is widely used to bias the analog circuits at an appropriate operating point, is one of the parameters that should be stable versus the temperature changes. This paper aims to design a stable and temperature-independent reference current with a low cost of fabrication and low power consumption, where the total consumption of power was only 1uW at 1V supply voltage. Since the mobility of carriers in the MOS devices is a temperature-dependent parameter, the new design uses the translinear principle-based square root circuit combined with two current source circuits to cancel the thermal effect of the carriers’ mobility on the produced current. The square root circuit of the proposed reference current circuit was designed to operate in the weak inversion region to achieve the linear property and was implemented by a 0.1μm CMOS technology. The simulation results recorded an output current of 25.06μA over a temperature range from 0 to 100 ℃ with a temperature coefficient of 92 ppm/°C. Thus, the proposed design of the reference current is suitable for low-power applications, especially for ultra-low-power op-amps

In this paper, we present a new impedance measurement integrated circuit (IC) for achieving a wideband coverage up to 10 MHz and low power consumption. A frequency-shift technique is applied to down-shift the input frequency, which ranges from 100 kHz to 10 MHz, into an intermediate frequency of 10 kHz, while the frequency-shifting is bypassed when the input frequency falls in the range from 100 Hz to 100 kHz. It results in 100 times relaxation of the requirement on the instrumentation amplifier (IA) bandwidth and the comparator delay, greatly reducing overall power consumption. The proposed IC employs the polar demodulation structure with a reference resistor that provides reference timing information avoiding any synchronization issue with the transmitter. In order to compensate for the comparator delay and nonlinearity of the IA, the reference magnitude measurement path is added, making only the mismatch of the circuit affects the accuracy. This allows for employing the auto-zeroing technique that can remove the offset but increase the absolute delay by using an additional capacitor to the comparator. The chip fabricated in a 0.18- μm CMOS technology consumes the power of 756 μW while covering the measurement frequency range from 100 Hz to 10 MHz and exhibiting the maximum magnitude and phase errors of 1.1 % and 1.9 °, respectively.

This paper presents a monolithically integrated CMOS receiver circuit for a pulsed time-of-flight (TOF) laser range-finder. The integrated CMOS Avalanche photodiode (APD) has an area of 300 × 300 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and demonstrates a breakdown voltage of ~10V. The receiver front-end consists of a Transimpedance Amplifier (TIA), a Post-Amplifier (PA) with an offset cancellation network and a 50Ω output buffer. The overall channel gain is 90dBΩ. The total area of the integrated circuit (IC) including bondpads and the APD is 1.48 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and it consumes 132 mW power without the output buffer. To the best of the author's knowledge, this is the first reported fully integrated TOF CMOS receiver including the photodetector for an indoor pulsed based laser rangefinder.

A high-speed transimpedance amplifier (TIA) has been designed and implemented in a low cost 0.35 µm CMOS technology. Combining the techniques of regulated cascode input stage, current shunt feedback and inductive-series peaking, the TIA achieves a transimpedance gain of 51 dBΩ and 3 dB bandwidth of 6 GHz, in the presence of a photodiode capacitance of 0.6 pF. This is believed to be the fastest TIA ever reported in 0.35 µm CMOS technology.

The excess noise of avalanche photodiodes (APDs) integrated in a high-voltage (HV) CMOS process and in a pin-photodiode CMOS process, both with 0.35-μm structure sizes, is described. A precise excess noise measurement technique is applied using a laser source, a spectrum analyzer, a voltage source, a current meter, a cheap transimpedance amplifier, and a personal computer with a MATLAB program. In addition, usage for on-wafer measurements is demonstrated. The measurement technique is verified with a low excess noise APD as a reference device with known ratio k = 0.01 of the impact ionization coefficients. The k-factor of an APD developed in HV CMOS is determined more accurately than known before. In addition, it is shown that the excess noise of the pin-photodiode CMOS APD depends on the optical power for avalanche gains above 35 and that modulation doping can suppress this power dependence. Modulation doping, however, increases the excess noise.

In many fields and in particular in astrophysical observations, a chronic problem is the photon-starving condition, which becomes severe when images are to be obtained in short acquisition times (from micro to milliseconds), as happens in hot areas of astrophysics: optical counterparts of high-energy gamma-ray bursts, study and interpretation of Supernovae bursts. CCDs are inherently unable to provide accurate measurements of such fast low-intensity transients at high frame rates. To respond to single photons, suitable detectors must provide output signals that are sufficiently high to be individually processed by electronic circuits. Therefore, only detectors with an internal mechanism that provides a high multiplication of charge carriers are suitable, namely vacuum tube photomultipliers (PMTs), solid-state avalanche photodiodes (APDs) and electron-multiplying CCDs (EMCCDs). In PMTs, the photocathodes available for the visible spectral range provide fairly good quantum efficiency and low noise, whereas cathodes for the red and near-infrared range have lower quantum efficiency and must be cooled to reduce the dark-count rate. PMTs are bulky, and so not suitable for assembly in large arrays, fragile, sensitive to electromagnetic disturbances and mechanical vibrations, require high supply voltages (1–2 kV) and are costly devices, particularly the high-performance models. EM-CCDs exploit an internal multiplication process to achieve sub-electron readout noise, thus being able to detect single photons. Their quantum efficiency is very high, and they are inherently suited to imaging applications. However, due to their readout technique, they cannot provide frame rates higher than a few kilo-frames per second, and cannot be used in extreme timeresolved measurements. Single photons can be detected efficiently by avalanche diodes operating in Geiger mode, known as Single-Photon Avalanche Diodes (SPADs). Avalanche photodiodes have the typical advantages of solid state devices (small size, low bias voltage, low power consumption, ruggedness and reliability, suited to building integrated systems). In the last few years, a new kind of planar semiconductor device has slowly but steadily come out, namely the silicon photomultiplier (SiPM), with promising features that, in some respect, could even replace traditional photomultiplier tubes (Kovaltchouk et al, 2005). Based on a Geiger mode avalanche photodiode elementary cell, it consists of an array of n

Laser ranging is a high-precision geodetic technique that plays an indispensable role in the field of geodynamics. Avalanche photodiodes (APDs) offer a series of advantages over other photodetector technologies, including photomultiplier tubes (PMTs) and superconducting single-photon detectors (SNSPDs). These advantages include high sensitivity, small size, high integration, and low power consumption, which have contributed to the widespread use of APDs in laser ranging applications. This paper analyses the key role of APDs in enhancing the accuracy and stability of laser ranging through the examination of application examples, including Si-APD and InGaAs/InP APD. Finally, based on the technological needs of laser ranging, the future development directions of APDs are envisioned, aiming to provide a reference for the research of photodetectors in high-precision and high-frequency laser ranging applications.

Modern society developed on the base of technology improvement. Progress in technologies based on computer, communication and automatic controls engineering all are depends on Integrated Circuit(IC). In the first half of 1990s, the electronic industry experienced an explosion in the demand for personal computers, cellular telephones, and high speed data communication devices. Vying for market share, vendors built products increasingly greater functionality, higher performance; lower cost, lower power consumption, and smaller in dimensions. To do these, vendors created highly integrated, complex systems with fewer IC devices and less printed-circuit-board (PCB) area. Minimizations of combinational logic functions before implementation in hardware have many advantages. A reduced number of gates considerably decreases the cost of the hardware, reduces the heat generated by the chip and most importantly increases the speed. Boolean functions may be simplified by algebraic means by applying the basic laws and theorems. However, this procedure is awkward because it lacks specific rules to predict each succeeding step in the minimization process for multi-input variables. The simplification by K- mapping has many disadvantages of redundant grouping and non-unique solution. But no method is effective for the simplification of Boolean functions, if it involves more than six variables. A few algorithm and modified technique are found in literature. This paper proposes an algorithm for reduction from multi input into two input variables.