Under the assumption that clock can be inputted to each register at an arbitrary timing, the minimum feasible clock period can be determined if delays between registers are given. This minimum feasible clock period might be reduced by register relocation maintaining the circuit behavior and topology. In this paper, we propose a gate-level register relocation method to reduce the minimum feasible clock period. The proposed method is a greedy local circuit modification method. We prove that the proposed method achieves the clock period achieved by retiming with delay decomposition, if the delay of each element in the circuit is unique. Experiments show that the computation time of the proposed method and the number of registers of a circuit obtained by the proposed method are smaller than those obtained by the retiming method in the conventional synchronous framework.

In this research, a sub-array preconditioner is applied to improve the convergence of conjugate gradient (CG) iterative solver in the fast multipole method and fast Fourier transform (FMM-FFT) implementation on a large-scale finite periodic array antenna with arbitrary geometry elements. The performance of the sub-array preconditioner is compared with the near-group preconditioner in the array antenna analysis. It is found that the near-group preconditioner achieves a little better convergence, while the sub-array preconditioner can be easily constructed and programmed with less CPU-time. The efficiency of the CG-FMM-FFT with high efficient preconditioner has been demonstrated in numerical analysis of a finite periodic array antenna.

This paper deals with the scattering of TE plane wave from a periodic grating with single defect, of which position is known. The surface is perfectly conductive and made up with a periodic array of rectangular grooves and a defect where a groove is not formed. By use of the modal expansion method, the field inside grooves is expressed as a sum of guided modes with unknown amplitudes. The mode amplitudes are regarded as a sum of the base component and the perturbed component due to the defect, where the base component is the solution in case of the perfectly periodic grating. An equation for the base component is obtained in the first step. By use of the base component, a new equation for the perturbed component is derived in the second step. A new representation of the optical theorem, relating the total scattering cross section with the reduction of the scattering amplitude is obtained. Also, a single scattering approximation is proposed to express the scattered field. By use of truncation, we numerically obtain the base component and the perturbed component, in terms of which the total scattering cross section and the differential scattering cross section are calculated and illustrated in figures.

This paper describes a CMOS voltage reference circuit which occupies small die area and has less than 1.25 V of output voltage. The reference voltage is determined by a resistor ratio, and it is possible to set the reference voltage from zero to near the supply voltage with the same temperature independence as those of Widlar's and Brokaw's bandgap voltage references. The temperature-independent reference voltage is formed by adding two voltages: the amplified fractional VBE (base-to-emitter voltage) of a bipolar transistor with a negative TC (temperature coefficient) and the amplified VT (thermal voltage) with a positive TC. When a reference voltage smaller than 1.25 V is required, the voltage gain of the amplifier for VBE becomes less than one, and the voltage gain of the amplifier for VT becomes small. This enables the size of bipolar transistors for VT generation to be small. The proposed voltage reference circuit was implemented in a standard 0.35-µm CMOS technology. A temperature-independent current source was also obtained from the same circuit. The results were a TC (temperature coefficient) of 46 ppm/ over 130 change, a line regulation of 2.2 mV/V for the 0.5 V reference voltage with 8.7 µA of current consumption in the voltage reference part, and a 6% change over 130 change for the 13 µA current source.

The uni-traveling-carrier photodiode (UTC-PD) is an innovative PD that has a unique operation mode in which only electrons act as the active carriers, resulting in ultrafast response and high electrical output power at the same time. This paper describes the features of the UTC-PD and its excellent performance. In addition, UTC-PD-based optoelectronic devices integrated with various elements, such as passive and active devices, are presented. These devices are promising for various applications, such as millimeter- and submillimeter-wave generation up to the terahertz range and ultrafast optical signal processing at data rates of up to 320 Gbit/s.

A micromirror for an external cavity diode laser is described. The mirror is supported by two sets of parallel torsion bars enabling piston motion as well as rotation. These motions are for realizing continuous wavelength tuning. Adjusting two rotations electrically, the pivot of the mirror rotation can be controlled. The long stroke of the vertical comb is realized by the deep three-dimensional structure prepared by the wafer bending method.

This paper studies rich superstable phenomena in a nonautonomous piecewise constant circuit including one impulsive switch. Since the vector field of circuit equation is piecewise constant, embedded return map is piecewise linear and can be described explicitly in principle. As parameters vary the map can have infinite extrema with one flat segment. Such maps can cause complicated periodic orbits that are superstable for initial state and are sensitive for parameters. Using a simple test circuit typical phenomena are verified experimentally.

We introduce an extension of Golay complementary sequences in which, for each sequence, there exists another sequence such that the sum of aperiodic autocorrelation functions of these two sequences for a given multiple L-shift (L≥1) is zero except for the zero shift. We call these sequences multiple L-shift complementary sequences. It is well-known that the peak-to-average power ratio (PAPR) value of any Golay complementary sequence is less than or equal to 2. In this paper, we show that the PAPR of each multiple L-shift complementary sequence is less than or equal to 2L. We also discuss other properties of the sequences and consider their construction.

If the signal is not Gaussian, then the power spectral density (PSD) approach is insufficient to analyze signals and we resort to estimate the higher order spectra of the signal. However, estimation of the higher order spectra is even more time consuming, for example, the complexity of trispectrum is O(N 4). This problem becomes even more serious when short time Fourier transform (STFT) is computed - computation of the trispectrum is required after every shift of the window. In this paper, a method to recursively compute trispectrum has been presented and it is shown that the computational complexity, for a window size of N, is reduced to be O(N 3) and is the same as the space complexity.

The diffraction of a transverse magnetic (TM) plane wave by a perfectly conductive surface made up of a periodic array of rectangular grooves is studied by the modal expansion method. It is found theoretically that the reflection coefficient approaches -1 but no diffraction takes place when the angle of incidence reaches a low grazing limit. Such singular behavior is shown analytically to hold for any finite values of the period, groove depth and groove width and is then demonstrated by numerical examples.

This paper treats transmission characteristics of periodic structure of ferrite gyrator circuit with both theory and experiment, which is loaded into usual distributed constant line with and without lumped capacitor. Following three types of periodic structure of gyrator circuit are proposed: basic structure of periodic gyrator circuit, quasi-LH gyrator circuit with series capacitance loading, and quasi-LH gyrator circuit with parallel capacitance loading. Moreover, replacing the parallel capacitance with a resistance, a periodic structure of isolator circuit is proposed. Scattering parameters of gyrator circuit are derived with help of equivalent circuit model. Left handed transmission behavior of backward wave is discussed from dispersion curves. Experiments were undertaken using periodic structure of dielectric microstrip line and gyrator circuit fabricated on the ferrite substrate. Experimental results having wide band nonreciprocal characteristics are discussed with theory.

Barker sequences have been used in many existing communications and ranging systems. Unfortunately, the longest known biphase and quadriphase Barker sequences are of lengths 13 and 15, respectively. In this paper, we introduce the so-called quasi-Barker sequences which achieve the minimum peak sidelobe level one within a certain window centered at the mainlobe. As our key results, all the best biphase and quadriphase quasi-Barker sequences of lengths up to 36 and 21, respectively, were obtained by an efficient computer search. These sequences may provide better multipath resistance and tracking accuracy in ranging applications.

We obtain an upper bound for the maximum aperiodic and odd correlations of the recently derived p-ary sequences from Galois rings [1]. We use the upper bound on hybrid sums over Galois rings [5], the Vinogradov method [4] and the methods of [5] and [6].

This paper studies the scattering of a TM plane wave from a perfectly conductive sinusoidal surface with finite extent by the small perturbation method. We obtain the first and second order perturbed solutions explicitly, in terms of which the differential scattering cross section and the total scattering cross section per unit surface are calculated and are illustrated in figures. By comparison with results by a numerical method, it is concluded that the perturbed solution is reasonable even for a critical angle of incidence if the surface is small in roughness and gentle in slope and if the corrugation width is less than certain value. A brief discussion is given on multiple scattering effects.

A nonreciprocal left-handed transmission line is proposed and investigated, which is composed of a normally magnetized ferrite microstrip line periodically loaded with inductive stubs but without capacitive loading. The circuit configuration becomes simpler than that of a nonreciprocal left-handed transmission line with both shunt inductive and series capacitive loadings. In the proposed structure, ferrite medium is employed as the substrate not only for the nonreciprocal characteristics but also for negative effective permeability that is essential to establish the left-handedness. After calculations of dispersion curves using equivalent circuit model, scattering parameters along with field patterns are estimated numerically with the help of electromagnetic simulation, and the experiments are also carried out. It is found that the band width of the proposed left-handed transmission line is relatively narrow but the structure still has the high isolation ratio of more than 30 dB.

Pt Schottky diode gas sensors for carbon monoxide (CO) were fabricated using slightly Si doped bulk GaN grown on sapphire substrate. The influence of diode size, Pt thickness, operating temperature on gas sensitivity was investigated. CO sensitivity was improved six times by optimizing the size and thickness of the Pt contact. Surface restructuring and morphology changes of Pt film were observed after thermal annealing. These changes are enhanced as the film thickness is reduced further and contribute to improve CO sensitivity.

Experimental result and theoretical analysis are reported for bias-voltage dependence of oscillation frequency in resonant tunneling diodes (RTDs) integrated with slot antennas. Frequency change of 18 GHz is obtained experimentally for a device with the central oscillation frequency of 470 GHz. The observed frequency change is attributed to the bias-voltage dependence of the transit time of electrons across the RTD layers, which results in a voltage-dependent capacitance added to RTD. Theoretical analysis taking into account this transit time is in reasonable agreement with the observed results. Voltage-controlled RTD oscillators in the terahertz range are expected from the theoretical results. A structure suitable for large frequency change is also discussed briefly.

Sensing elements based on AlGaN/GaN HEMT and Schottky diode structures have been investigated in relation with the strain sensitivity of their characteristics. Piezoresistance of the Al0.3Ga0.7N/GaN HEMT-channel as well as changes in the current-voltage characteristics of the Schottky diodes have been observed with gauge factor (GF) values ranging between 19 and 350 for the selected biasing conditions. While a stable response to strain was measured, the observed temperature dependence of the channel resistance demonstrates the need for a systematic characterisation of the sensor properties to allow compensation of the observed temperature effects.

We have fabricated and investigated InGaAs Esaki tunnel diodes, grown on GaAs or InP substrates, of varied defect densities. The tunnel diodes exhibit the same I-V characteristics in spite of the variation of defect density. Under the simple thermal annealing and forward current stress tests, the change in the valley current was not observed, indicating that defects were not increased. On the other hand, the reduction in the peak current due to the carbon diffusion was observed under both tests. The diffusion was enhanced by the stress current owing to the energy dissipation associated with the nonradiative electron-hole recombination. From the reduction rates of the peak current, we obtained the thermal and current-enhanced carbon diffusion constants in InGaAs, which are independent of defect density. Although thermal diffusion of carbon in InGaAs is comparable with that in GaAs, the current-induced enhancement of diffusion in InGaAs is extremely weaker than that in GaAs. The difference between activation energy of thermal and current-enhanced diffusion is 0.8 eV, which is independent of stress current density and close to InGaAs bandgap energy. This indicates that the current-enhanced diffusion is dominated by the energy dissipation associated with nonradiative band-to-band recombination. This enhancement mechanism well explains that the current-induced enhancement is independent of defect density and extremely weak. We also have found that the current-enhanced diffusion constant is approximately proportional to the square of current density, suggesting that the recombination in the depletion layer dominates the current-enhanced diffusion.

We present room temperature current voltage characteristics from SiGe interband tunneling diodes epitaxially grown on highly resistive Si(001) substrates. In this case, a maximum peak to valley current ratio (PVCR) of 5.65 was obtained. The possible integration of a SiGe tunnel diode with a strained Si transistor lead us to investigate the growth of SiGe interband tunneling diodes on Si0.7Ge0.3 virtual substrates. A careful optimization of the layer structure leads to a maximum PVCR of 1.36 at room temperature. The latter value can be further increased to 2.26 at 3.7 K. Our results demonstrate that high quality SiGe interband tunneling diodes can be realized, which is of great interest for future memory and high speed applications.