This paper presents a general circuit structure based on piecewise constant approximation method for designing high-rate ultra-wideband (UWB) pulse generators. By changing the pulse duration and the number of approximation segments, both the bandwidth and the center frequency of UWB signals are tuned. The pulse generator modulates different carrier frequencies into signals with Gaussian envelop to spread the signal spectrum over the 3.1-10.6-GHz sub-bands. Also, the proposed modulator structure can be easily adopted to generate pulses with 528-MHz bandwidth within the three sub-bands in the 3.1-5-GHz range.
This paper describes a combined modulation scheme for TH-UWB radio systems using on-off keying (OOK) and pulse shape modulation (PSM). For this scheme, a set of orthogonal pulses is used to represent bits in a symbol. These orthogonal pulses are transmitted simultaneously in the same time slot resulting in a composite pulse. The proposed transmission scheme can achieve higher data rate by using fewer number of pulses and receiver correlators than PSM. Due to the presence of OOK, the proposed scheme requires minimum energy and is applicable for energy constrained TH-UWB systems.
In this letter, we propose a new approach to speech enhancement based on a complex Laplacian probability density function (pdf). With a use of a goodness-of-fit (GOF) test, we discover that the complex Laplacian pdf is more desirable to describe noisy speech distribution than the conventional Gaussian pdf for speech enhancement. The likelihood ratio (LR) is computed and then applied to computation of the speech absence probability in the speech enhancement algorithm. Our evaluation shows that the proposed complex Laplacian pdf scheme provides further speech quality enhancement compared with the conventional method through a number of objective tests.
We describe a polarization-maintaining (PM) λ/4-shifted DFB Er-doped fiber laser (EDFL), in which optical pulsation effects caused by Er3+ ion-pairs were successfully removed by co-doping erbium fiber with 12wt% aluminum. Stable CW operation was realized at a pump power of 100mW. The laser exhibited single longitudinal-mode oscillation with a single polarization. The output power, linewidth of the longitudinal mode, and RIN at the relaxation oscillation frequency were 0.5mW, 82kHz, and -79dB/Hz at a pump power of 100mW, respectively. Stable operation was also obtained at a pump power of 140mW, where the above values were improved to 0.8mW, 43kHz, and -92dB/Hz, respectively.
Terahertz spectroscopy has rapidly progressed, and is being applied to various research fields as a new non-invasive examination method. Scientific analysis is important for the conservation of art, as it can help to reveal the history of a work and to determine the proper materials for its restoration. Mid-infrared spectroscopy and X-ray analysis are currently used to identify organic and inorganic materials, respectively. Terahertz spectroscopy is expected to identify composites themselves, and to give clear and direct information for art conservation. We have collected terahertz spectra of various historical and modern materials, and found that terahertz spectroscopy can distinguish the pigments, binders and their mixtures. The experimental results prove that terahertz spectroscopy as a new non-invasive examination method can contribute to art history and to restorations. The material database can also contribute to other fields such as earth science, the printing industry, and the food and pharmaceutical research fields.
In this paper, we propose and demonstrate an Ant-based constraint-based routing for transparent optical networks based on ASE noise accumulation along the lightpath. Our proposed algorithm selects the route based on the minimum ASE noise, leading to lower blocking probability. The numerical results show that the proposed algorithm outperforms the traditional shortest path routing algorithm. The results show that these ASE have a significant impact on transparent networks. Careful gain choice, low noise figure are strongly desired for the accomplishment of efficient, cost-effective, high capacity WDM transparent optical networks.
We propose a new pixel structure of pulse-width-modulation (PWM) CMOS active pixel sensor with a small pixel size performing a pixel-level single-slope A/D conversion to realize a low and single power supply operation. The pixel is composed of only three transistors without pixel-circuit sharing, and has a gate-common amplifier that compares a photodiode voltage on the gate node with a ramp signal on the source for A/D conversion. We have fabricated a 128×96-pixel prototype imager with an on-chip ramp generator and bootstrap circuits in a 0.35-µm CMOS technology, and successfully demonstrated image acquisition with a 1.4-1.8-V single power supply.
This paper presents a new high speed current mirror with continuous gain adjustment. Based on this current mirror, a variable gain current amplifier is designed in 0.18µm CMOS technology. The current gain of the amplifier can be continuously varied from 0dB to 20dB while the bandwidth of the circuit remains above 100MHz. The circuit consumes 0.9mW from 1.5V supply.