This paper presents a new single-stage fully-differential class AB folded-cascode operational transconductance amplifier (OTA) for low-voltage and fast-settling switched-capacitor circuits in pure digital CMOS technology. The proposed OTA employs class AB operation in both the input-stage and output current source transistors resulting in large slew rate, enhanced unity-gain bandwidth and DC gain. The method to build the class AB operation in the output current source transistors is very simple which does not need any extra circuit and power consumption. HSPICE simulation results are presented to show the usefulness of the proposed OTA's structure.
This paper describes a new association of a high-Q pseudo 8-path switched-capacitor (S-C) bandpass filter and its command circuit made up by a ring VCO with `XOR' gates. The proposed circuit presents the possibility of tuning over a radio-frequency (RF) broadband allowing to sweep different channels with a high quality factor. Designed with CMOS process (0.35µm, for instance), this circuit is intended to replace the surface acoustic wave (SAW) filters in modern wireless receivers. Measurements carried out on a circuit demonstrator show a tunable center frequency range of 200MHz [300-500MHz], with a quality factor higher than 300.
We propose a monolithic external-cavity vertical-cavity surface emitting laser (VCSEL) for achieving ultra-high speed direct modulation beyond the limit of a relaxation oscillation frequency. We present the modeling of small-signal and large signal modulation characteristics of VCSELs with optical feedback. It is predicted that a 3 dB-modulation bandwidth can be increased by 50% with optimizing an external cavity length. Also, better eye opening can be expected in 40Gbps direct modulation.
In this paper, we present a novel Adaptive Pre-task Assignment (APA) strategy for heterogeneous distributed raytracing system. The strategy has the following main features: i) the master pre-task assignment to each node/worker. The amount of sub-task size for each node is proportional to the node's performance. ii) Reduction in the inter-processes communication, nodes idle time cost overhead and load imbalance, when compared to the traditional Runtime Task Scheduling (RTS) strategies. The measured results of our proposed (APA) strategy have shown a significant improvement in speedup over RTS strategy.
Speech quality evaluation is a very important research topic. Mean Opinion Score (MOS) is reliable but the listening test is very expensive, time consuming, and sometimes impractical. The existing objective quality assessment methods require either the original speech or complicated computation model, which makes some applications of quality evaluation impossible. We propose to use digital audio watermarking to evaluate the quality of speech. Our method does not need original signal or computation model. The experimental results show that the method yields accurate quality scores which are very close to the results of PESQ.
In this paper, we present a numerical investigation on the performance of 40Gbit/s polarization modulation (POLSK) in ultra-long haul transmission systems by using optical phase conjugator (OPC). The effects of both semiconductor optical amplifier (SOA) and dispersion shifted fiber (DSF) based OPCs on the 10,000km system are investigated. It is found that only 53 SOA based OPCs are needed in order to achieve the bit-error-rate (BER) of less than 10-9 in comparison to 69 DSF based OPCs. In addition, with the introduction of 100 SOA based OPCs, the system can withstand the fiber nonlinearity of up to 2.0W-1km-1 for a 15,000km transmission distance.
We propose and demonstrate the Coherent Optical Multiple-Input Multiple-Output (COMIMO) communication technique. In analogy to the spatial diversity in wireless communication, the concept exploits the modal diversity, inherent in a multi-mode fiber (MMF), to transmit independent data channels through a single fiber without the need for wavelength division multiplexing. Central to the MIMO concept is the requirement for sufficient modal diversity in the fiber. The coherent-optics implementation is the key as it ensures that the diversity requirement is met for practically any fiber length and at any data rate. A 2x2 proof-of-concept COMIMO system is experimentally demonstrated.
We demonstrate a multi-user, 10Gb/s spectrally phase coded O-CDMA system with hybrid chip and slot-level timing coordination utilizing low power nonlinear processing. A new double Hadamard coding scheme is demonstrated to enable both chip-level timing coordination and full interference suppression without the need for synchronous detection.
Two novel configurations of second-order sinusoidal oscillators have been presented which employ only unity-gain voltage followers and current followers as active elements. The workability of the new circuits has been demonstrated by the SPICE simulations of their CMOS-implementable versions.