Timing constraints for high-speed counterflow-clocked pipelining

With the escalation of clock frequencies and the increasing ratio of wire-to gate-delays, clock skew is a major problem to be overcome in tomorrow's high-speed very large scale integration (VLSI) chips. Also, with an increasing number of stages switching simultaneously comes the problem of higher peak power consumption. In our prior work, we have proposed a novel scheme called counterflow-clocked (C²) pipelining to combat these problems, and discussed methods for composing C² pipelined stages. In this paper, we analyze in great detail the timing constraints to be obeyed in designing basic C² pipelined stages, as well as in composing C² pipelined stages. C² pipelining is well suited for systems that exhibit mostly unidirectional data flows as well as possess mostly nearest neighbor connections. C² pipelining eases the distribution of high-speed clocks, shortens the clock period by eliminating global clock signals, allows natural use of level-sensitive dynamic latches, and generates less internal switching noises due to the uniformly distributed latch operation. By applying C² pipelining and its composition methods to build a system, VLSI designers can substitute the global clock-skew problem with many local one-sided delay constraints     

The identification of candidate transitions for optically pumped far infrared lasers: Methyl halides and D2O

Two hundred and forty-four candidate transitions for optically pumped far infrared lasers have been identified in C¹²H3F, C¹³H3F, C¹²D3F, C¹²H3Cl³⁵, C¹²H3Cl³⁷, C¹²H3Br⁷⁹, C¹²H3Br⁸¹, and D2O using as candidate pump lines, 781 in number, the isotopic forms of CO2, the sequence and hot bands of C¹²O2¹⁶, and the N2O bands. The dominant transition parameters responsible for strong emission from TEA, CW, and long pulse modes of operation were identified by a correlation between known experimental behavior and the pertinent transition parameters, the results being that strong TEA laser emission correlates with ground state population while strong CW and long pulse emission correlate with absorption coefficient. The candidate transitions were subsequently selected on the basis of these parameters using calculated transitions and assignments based on band data from high resolution laser-Stark spectroscopy and measured candidate pump frequencies.     

Optoelectronic logic operations by cleaved-coupled-cavity semiconductor lasers

We propose and demonstrate the operation of a new opto-electronic scheme of performing the set of logic operations including AND, OR, EXCLUSIVE OR, and INVERTER. The present scheme is not based on optical bistability, but rather utilizes the unique characteristics of the newly developed cleaved-coupled-cavity (C³) semiconductor laser. The C³laser always operates in a single longitudinal mode and the lasing wavelength can be tuned by varying the current levels (pulsed or dc) injected into the two optically coupled stripe-geometry laser diodes. Unlike the case of optical bistable devices (based on FP semiconductor diodes), which operate on optical inputs and produce optical outputs, the present device operates on electrical inputs and produces optical outputs. In addition to performing the logic operations, this can also serve as an electrical-optical interface. Further, the present scheme is also capable of producing multiple different logic outputs simultaneously for the same two inputs. Results from time-resolved spectral measurements using InGaAsP buried crescent lasers (lambda = 1.3 mum) showed that the switching time was in the subnanosecond region. This indicates that extremely high bit rate information processing in the Gbit/s range can be achieved by using the present C³semiconductor lasers as the logic gates. The present C³lasers are very compact (sim300 times sim200 mum) and rigid, and the scheme can be applied to semiconductor lasers with other types of stripe geometries and wavelengths.     

6 GHz direct frequency modulation of cleaved-coupled-cavity channeled-substrate buried-heterostructure lasers

The measured intensity modulation (IM) and frequency modulation (FM) characteristics of single-cavity channeled-substrate buried-heterostructure (CSBH) lasers and cleaved-coupled-cavity (C³) CSBH lasers are described. If the bias is well above threshold, the lasers have -3 dB IM bandwidths of approximately 800 MHz. In contrast, the FM response rolls off less rapidly, and efficient FM operation up to 6 GHz is possible. The IM and FM responses of C³CSBH lasers are similar to single-cavity CSBH lasers provided the modulated cavity is above threshold. If the modulated cavity is below threshold, the FM response of the C³laser is larger but rolls off rapidly for modulation frequencies above 200 MHz.     

Calculable field generation using TEM cells applied to thecalibration of a novel E-field probe

This paper examines the calculable generation of electromagnetic fields for calibration purposes using TEM cells. In order to enlarge the bandwidth the use of a circular coaxial calibration cell (C³ cell) is proposed. Based on generalized telegraphist's equations the field is calculated. Results are compared with other common TEM cells (Crawford (1974) cell, GTEM cell). For field measurements a new isotropic field probe is considered. The proposed probe uses only one electrically short dipole with a diode detector and enables the measurement of both the magnitude and the polarization direction of an electromagnetic field. The manufactured probe was calibrated utilizing the C³ cell     

Bit-error-rate saturation due to mode-partition noise induced by optical feedback in 1.5-µm single longitudinal-mode C3and DFB semiconductor lasers

We report first measurements of the effect of optical feedback on the bit error rate (BER) as a function of received power of single longitudinal mode cleaved-coupled cavity (C³) and distributed-feedback (DFB) semiconductor lasers. Mode-partition noise, induced by the optical feedback, can cause a bit error-rate floor for large optical feedbacks, but it is shown that high-performance C³lasers and especially DFB lasers can withstand very large optical feedbacks without system degradation.     

A note on [A, B, C, D]

For arbitrary linear passive networks it is possible to suggest bounds of the type f(A, B, C, D) ≥ 0. A novel inequality is presented for linear reciprocal resistive two-ports: A²+ B²+ C²+ D²+ AB + CD ≥ √3 It is common practice in electrical engineering to consider a two-port as an operator represented by a 2 × 2 matrice acting on the space of the input signals.     

An investigation of the frequency stability and temperature characteristics of 1.5 µm coupled-cavity injection lasers

It has been demonstrated, both theoretically and experimentally, that a coupled-cavity injection laser is capable of oscillating with a single-frequency output. However, because of the nature of the constructive and destructive interference of the optical fields inside the coupled cavities, the frequency of the lasing mode is subject to change due to variations in the refractive indexes of the active media, which in turn are functions of both injected carrier density and junction temperature. In this paper, the frequency stability (mode hopping) and temperature characteristics of such lasers are computed numerically for two specific cases based on a rate equation formalism previously reported. The behavior of experimental lasers fabricated as cleaved-coupled-cavity (C³) devices showed good agreement with the computed result, except that the measured light-versus-current (L-I) curves were "kinky." Each kink was found to signify mode hopping, which is believed to be caused by incomplete electron pinning above lasing threshold. The speed of mode switching from the initial lasing mode to the adjacent lasing mode was less than 1 ns and a hysteresis was observed when both cavities were operated with large gains. Experimental results have shown that when the C³laser is operated in a steady-state single-frequency output the photon fluctuations are significantly reduced, which implies that the coupled-cavity laser can be used as a CW signal source, in conjunction with an external modulation, which is free from partition noise at gigabit per second data rates.     

Regenerative switching characteristics of a novel electrical oroptical base-controlled AlGaAs/GaAs quantum-well heterojunction bipolartransistor

A report is presented on the regenerative switching characteristics of a novel AlGaAs/GaAs quantum-well heterojunction bipolar transistor (QWHBT) with an electrically or optically controlled base grown by molecular beam epitaxy (MBE). This double-barrier QWHBT exhibits excellent electrical switching characteristics of 7 V and 0.03 A/cm² at the switching condition and 4.5 V and 3.2 A/cm² at the holding condition. When the device is operating as an optical switch, the optical base-controlled sensitivity is 6×10 ^-3 V/μW. The effects of temperature on the device performance were evaluated at 77 and 300 K. The results show that it may be used as an all-optical switch (flip-flop) for optical parallel image processing     

Robust control of positioning systems with a multi-step bang-bang actuator

A nonlinear control scheme for preventing the limit cycle due to the nonlinearity of the multi-step bang-bang actuator in mechanical position control systems is proposed. A linearized model, sinusoidal input describing function (SIDF), for a multi-step bang-bang actuator is introduced to compensate the nonlinearity of the multi-step bang-bang actuator. Using that model, an H_∞ robust controller for position control systems with a bang-bang actuator is proposed by loop shaping techniques with normalized coprime factorization stabilization to address the robustness. The proposed scheme requires a smaller deadband as a result of compensating the nonlinearity of the bang-bang actuator. A single-axis servo system is implemented in order to verify the proposed control scheme experimentally. Experimental results show that the controller can satisfy the special interest, silent contact switching of the actuator.     

Active spectral stabilization of cleaved-coupled-cavity (C3) lasers

A stabilization technique which will maintain a cleaved-coupled-cavity (C³) laser in single-mode operation over a wide current and temperature range is proposed and demonstrated.     

An optical switching and routing system using frequency tunable cleaved-coupled-cavity semiconductor lasers

A 1 × 4 optical switch based on a frequency tunable cleaved coupled cavity (C³) laser and a grating demultiplexer is demonstrated. The switch, which can easily be expanded to a generalN times Nswitch WithNas high as 13 has a 2 ns access time with negligible crosstalk between the channels.     

Moving naval C4I into the next century

The combination of command, control, communications, computers and intelligence is known in the military as C⁴I. The naval C⁴I initiative is defining a future architecture that is based on information management with one objective in mind: to bring naval C⁴I to the next level of integration and interoperability in the joint war fighting arena for the advantages it brings to the warrior. We discuss the path we are taking to a more integrated C⁴I (IC⁴I) system. We also discuss what we have done to both define and bound the naval C⁴I universe; where we are on the path to the IC⁴I system; the challenges we face on our way; and how we intend to surmount them     

Actively clamped zero-current-switching quasi-resonant convertersusing IGBTs

Conventional zero-current-switching quasi-resonant power converters (ZCS-QRCs) suffer from the disadvantages of high switch current stress and variable switching frequency. This paper proposes the use of a “current-clamping circuit” to overcome these disadvantages. By incorporating such a circuit into the family of ZCS-QRCs, a new family of actively clamped ZCS-QRCs using insulated gate bipolar transistors (IGBTs) is derived. These power converters feature high (and constant) switching frequency and zero-current turn-off (without increased current stress), which are particularly useful for high-power applications where minority-carrier semiconductor devices (such as IGBTs and bipolar junction transistors) are used as power switches. The design criteria, simulation and experimental results are reported     

Influence of Injector Doping Concentration on the Performance of InP-Based Quantum-Cascade Lasers

The influence of injector doping concentration N_inj on the performance of InP-based quantum-cascade (QC) lasers is investigated for devices emitting around 9.2-mum wavelength and injector doping concentrations between 1times10¹⁷ cm^-3 and 3times10¹⁷ cm^-3. The threshold current density, the dynamic range, the maximum emitted output power as well as the maximum operating temperature are found to increase with increasing N _inj. All in all, there exists no optimal value of N_inj per se. In fact, the injector doping concentration has to be adjusted individually depending whether emphasis is placed on obtaining low threshold current densities or on high-power operation     

Molecular beam epitaxy growth of TmP/GaAs and transistor action inGaP/TmP/GaAs heterostructures

The growth of thulium phosphide (TmP) by molecular beam epitaxy (MBE) on GaAs substrate is reported. Good epilayer quality was demonstrated through X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM) analysis. The closely lattice matched TmP layer was n-type with an electron concentration of 1.6×10²¹ cm^-3 and a room temperature mobility of 4.8 cm²V^-1s^-1. The Schottky barrier height determined from 1/capacitance² (1/C²) versus voltage (V) measurements is about 0.81 eV which agrees well with the value obtained through the current-voltage (I-V) measurements. In this work, we also report transistor action in a GaP/TmP/GaAs structure, for which chemical bonding techniques were employed. From I-V measurements, a common base current gain α≈0.55 at V_CB=0 was obtained at room temperature     

Ultrashort-Pulse High-Power Yb3+-Doped Fiber Amplifiers

Ultrashort optical pulse propagation in high-power Yb³⁺-doped fiber amplifiers (YDFA) is studied using a spectrally resolved nonlinear power equation for the coupled pulse components. The Yb³⁺ ions transitions are modeled using a rate equation. Examples for high-power YDFAs with normal dispersion show good qualitative agreement with experimental results. We analyze the effects of the incident pulse wavelength, pulse peak power, Yb³⁺ concentration, pump filling factor, fiber length, pumping configuration, pump power and nonlinear index, on the intensity distribution of short amplified pulses. We also demonstrate the spectral compression of an initially negative-chirped pulse.     

节能型三相桥式零电流开关整流器

为使三相桥式整流器实现节能运行,提出了一种节能型三相桥式零电流开关整流器拓扑结构,在各相桥臂上的辅助谐振电路处于工作状态时,整流器的开关器件能完成零电流软关断.三相桥式整流器通常以绝缘栅双极型晶体管（Insulated Gate Bipolar Transistor,IGBT）作为开关器件,实现零电流软关断能消除IGBT拖尾电流产生的关断损耗.分析了电路工作过程,在三相3kW样机上的实验结果表明开关器件实现了零电流软切换.因此,该拓扑结构可实现以IGBT作为开关器件的三相桥式整流器的节能运行.     

GaN based transistors for high power applications

Unique properties of GaN and related semiconductors make them superior for high-power applications. The maximum density of the two-dimensional electron gas at the GaN/AlGaN heterointerface or in GaN/AlGaN quantum well structures can exceed 2×10¹³ cm⁻², which is more than an order of magnitude higher than for traditional GaAs/AlGaAs heterostructures. The mobility-sheet carrier concentration product for these two dimensional systems might also exceed that for GaAs/AlGaAs heterostructures and can be further enhanced by doping the conducting channels and by using “piezoelectric” doping. Current densities over 20 A mm⁻¹ can be reached in GaN-based high electron mobility transistors (HEMTs). These high current values can be combined with very high breakdown voltages in high-power HEMTs, which are expected to reach several thousand volts. Recent Monte Carlo simulations point to strong ballistic and overshoot effects in GaN and related materials, which should be even more pronounced than in GaAs-based compounds but at much higher electric fields. This should allow us to achieve faster switching, minimizing the power dissipation during switching events. Self-heating, which is unavoidable in power devices, raises operating temperatures of power devices well above the ambient temperature. For GaN-based devices, the use of SiC substrates allows to combine the best features of both GaN and SiC technologies; and GaN/SiC-based semiconductors and heterostructures should find numerous applications in power electronics.     

MBE grown n+-i-δ(p+)-i-n+GaAs V-groove barrier transistor

The three-terminal n⁺-i-δ(p⁺)-i-n⁺V-groove barrier transistor (VBT) has been successfully fabricated by molecular beam epitaxy (MBE). The base terminal is connected to the δ(p⁺), the thin p⁺layer, by depositing aluminum on the etched V-groove. The demonstrated device possesses high potential of ultra-high-frequency (f_{r} > 30-GHz), high-power, and low-noise capability due to carriers transporting by thermionic emission and being controlled by the base-emitter bias.