A new and efficient open addressing technique, called improved exponential hashing, is proposed. We show that improved exponential hashing has the ability to spread table elements more randomly than the widely used double hashing, and at the same time produces full length probe sequences on all table elements. We demonstrate experimentally that improved exponential hashing performs significantly better than double hashing for clustered data. Also, some theoretic analysis is provided along with the experimental results.
This paper presents a wide tuning range LC-VCO using an on-chip variable inductor to extend tuning range. The VCO was fabricated using 0.35µm CMOS process. The tuning range was found to be 37.8% without degradation of phase noise by inductance tuning. Wide tunable VCO with an on-chip variable inductor is one of the key circuits of reconfigurable RF circuit.
An annealing study of the AlGaN/GaN 2DEG structure for HEMTs with or without SiN surface passivation films was conducted with the AlGaN layer thickness dependence taken into consideration. Without SiN, the sheet resistance of the samples with thin AlGaN layers increased significantly upon annealing at 620 and 800°C. In contrast, samples with SiN were thermally stable after annealing at up to 800°C even when the AlGaN layer was as thin as 152Å. TEM observations revealed that neither surface roughness nor interfacial diffusion at the SiN/AlGaN interface occurred due to annealing. The SiN layer is very effective for passivating an AlGaN surface and improving the thermal stability of a thin-AlGaN 2DEG channel.
The attainable Frame Error Rate (FER) in satellite burst communication is much too high when a classical Costas Loop is used as the carrier synchronizer. This high FER is due to cycle slips and hang-up of the Costas Loop. We demonstrate the potential to achieve a FER of 3×10-6 using 3 parallel Kalman tracking loops with their initial frequencies spaced apart. We also propose an algorithm for selecting the correct loop for demodulation and use data aided and optimal phase detection for the preamble and payload respectively. This dramatic improvement is at a reasonable complexity.
A new gain clamping scheme in double-pass L-band erbium-doped fiber amplifier (EDFA) based on partial reflection of amplified spontaneous emission (ASE) into the EDFA is demonstrated using a narrowband fiber Bragg grating as an ASE reflector. The proposed amplifier achieves a good gain clamping characteristic up to -12dBm of input signal power with gain variation of less than 0.5dB from a clamped gain of 22.0dB. The noise figure within the gain-clamping region is maintained below 5.0dB. The low noise figure is achieved since the proposed amplifier is not based on lasing mechanism. The proposed amplifier is also expected to be free from the relaxation oscillation problem.
Affine arithmetic (AA) is a variant of interval arithmetic. In AA, it is difficult to realize the efficient nonlinear binomial operations. The purpose of this paper is to propose a new dividing method which consists of a reciprocal and the best multiplication. And the performances of the new method and the conventional method are compared through some numerical examples.
In this paper, we present a full-wave analysis of microstrip lines printed on variable thickness substrates using the method of lines (MoL). The propagation constant of a microstrip line in the interface of one dielectric is computed as a function of different shape characteristics. The results are compared with those obtained in previous research, especially with those using the discrete mode matching technique (DMM). Good agreement is found between the results. Furthermore, the convergence behavior of the method of lines is examined and finally, we show some numerical results, obtained with analyzing this structure in a large band of frequencies.
The ultra wideband (UWB) radio has been a promising technology for the short range wireless systems. The frequency-dependent behavior of the antennas are not negligible in UWB systems, especially in the impulse radio (IR). This letter presents the extension of the Friis' transmission formula for the link budget estimation of UWB radio, considering the transmit signal waveform and the imperfect antennas. The results presented here give the upper bound of the transmission gain, irrespective of the waveform distortion due to the frequency response of the antenna.
We developed a dry etching process suitable for fabricating InGaAlAs laser mesa stripes. We used optimized Cl2/N2 ECR plasma for etching an InGaAlAs laser multilayer structure. This Cl2/N2 ECR plasma led to a uniform etching rate and an anisotropic profile using a nitrified side-protection mechanism. This smooth and anisotropic dry etching produced a well-matched interface for semi-insulated Fe-InP regrowth. It also enabled successfully fabricating an InGaAlAs buried heterostructure laser. The laser showed stable operation at 85°C and long-term reliability over 5000 hrs.
High-impedance quarter-wavelength (λ/4) coplanar waveguide (CPW) transformer is characterized as an alternative J-inverter element with enhanced coupling degree. After the frequency-related coupling behavior of this transformer is investigated, a novel two-stage λ/4 CPW bandpass filter is constructed with widened passband and good harmonic suppression. Its filtering performance is first studied versus varied inductive coupling at center and then optimally designed toward minimizing the insertion loss in the passband. Predicted filtering characteristics are in final confirmed by our experiment of a fabricated filter circuit over a wide frequency range.