Transmission performance of 10-Gb/s 1550-nm transmitters using semiconductor optical amplifiers as booster amplifiers

We have demonstrated the transmission performance of 10-Gb/s transmitters based on LiNbO/sub 3/ modulator using semiconductor optical amplifiers (SOAs) as booster amplifiers. Utilizing the negative chirp converted in SOAs and self-phase modulation induced by high optical power, we can successfully transmit 10-Gb/s optical signals over 80 km through the standard single-mode fiber with the transmitter using SOAs as booster amplifiers. SOAs can be used for booster amplifiers with a careful adjustment of the operating conditions. In order to further understand an SOA's characteristics as a booster amplifier, we model SOAs and other subsystems to verify the experimental results. Based on the good agreement between the experimental and simulation results, we can find the appropriate parameters of input signals for SOAs, such as extinction ratio, rising/falling time, and chirp parameter to maximize output dynamic range and available maximum output power (P/sub o,max/).     

Lost retransmission detection for TCP SACK

There have been a lot of works to avoid retransmission timeout (RTO) of transmission control protocol (TCP) that takes place in an unnecessary situation. However, most current TCP implementations, even if selective acknowledgment (SACK) option is used, do not have a mechanism to detect a lost retransmission and avoid subsequent RTO. In this letter, we propose a simple modification that enables a TCP sender using SACK option to detect a lost retransmission, which is called TCP SACK+ in simple. We use a stochastic model to evaluate the performance of TCP SACK+. Numerical results evaluated by simulations show that TCP SACK+ improves the loss recovery of TCP SACK significantly in presence of random losses.     

镍层耐硝酸腐蚀性测试——一种简单的预先探测ENIG镍层“黑盘”现象的测试方法

随着更加精细的SMT、BGA等表面贴装技术的运用,化学沉镍金(ENIG)作为线路板最终表面处理得到了越来越广泛的应用,同时可怕的“黑盘”现象也随之更广泛地“流行”起来,直接导致贴装后元器件焊接点不规则接触不良。为了贯彻执行最好的流程控制和采取有效的预防措施,了解这种焊接失败的产生机理是非常重要的,及早的观测到可能发生“黑盘”现象的迹象变得同样关键。本文介绍了一种简单的预先探测ENIG镍层“黑盘”现象的测试方法-镍层耐硝酸腐蚀性测试,这种测试可以用于作为一种常规的测试方法监测一般化学沉镍溶液在有效使用寿命范围内新鲜沉积的镍层的质量。利用Weibull概率统计分析在不同的金属置换周期(MTO)下镍层的可靠性能表现。结合试验结果得出了一个镍层耐硝酸腐蚀性的判定标准。     

Enhanced thermal stability of a sputtered titanium-nitride film as a diffusion barrier for capacitor-bottom electrodes

The effect of a thin RuO_x layer formed on the Ru/TiN/doped poly-Si/Si stack structure was compared with that on the RuO_x/TiN/doped poly-Si/Si stack structure over the post-deposition annealing temperature ranges of 450–600°C. The Ru/TiN/poly-Si/Si contact system exhibited linear behavior at forward bias with a small increase in the total resistance up to 600°C. The RuO_x/TiN/poly-Si/Si contact system exhibited nonlinear characteristics under forward bias at 450°C, which is attributed to no formation of a thin RuO_x layer at the RuO_x surface and porous-amorphous microstructure. In the former case, the addition of oxygen at the surface layer of the Ru film by pre-annealing leads to the formation of a thin RuO_x layer and chemically strong Ru-O bonds. This results from the retardation of oxygen diffusion caused by the discontinuity of diffusion paths. In particular, the RuO_x layer in a nonstoichiometric state is changed to the RuO₂-crystalline phase in a stoichiometric state after post-deposition annealing; this phase can act as an oxygen-capture layer. Therefore, it appears that the electrical properties of the Ru/TiN/poly-Si/Si contact system are better than those of the RuO_x/TiN/poly-Si/Si contact system.     

Wireless-adaptive fair scheduling for multimedia stream

As packet cellular networks are expected to support multimedia services, the authors incorporate the multimedia QoS requirements into the design of a new scheduling algorithm. The proposed wireless-adaptive fair scheduling tries to allocate time slots for each user with fair share by considering the varying channel condition while reflecting the stream requirements and achieving high throughput.     

InP D-HBT ICs for 40-Gb/s and higher bitrate lightwave transceivers

The combination of device speed (f/sub T/, f/sub max/ > 150 GHz) and breakdown voltage (V/sub bceo/ > 8 V) makes the double heterojunction bipolar InP-based transistor (D-HBT) an attractive technology to implement the most demanding analog functions of 40-Gb/s transceivers. This is illustrated by the performance of a number of analog circuits realized in an InP D-HBT technology with an 1.2- or 1.6-/spl mu/m-wide emitter finger: a low phase noise push-push voltage-controlled oscillator with -7-dBm output power at 146 GHz, a 40-GHz bandwidth and low-jitter 40-Gb/s limiting amplifier, a lumped 40-Gb/s limiting driver amplifier with 4.5-V/sub pp/ differential output swing, a distributed 40-Gb/s driver amplifier with 6-V/sub pp/ differential output swing, and a number of distributed preamplifiers with up to 1.3-THz gain-bandwidth product.     

Magnetic effects of direct ion implantation of Mn and Fe into p-GaN

In p-GaN implanted with Mn (3×10¹⁶ cm⁻² at 250 keV), the material after annealing shows ferromagnetic properties below 250 K. Cross-sectional transmission electron microscopy (TEM) revealed the presence of platelet structures with hexagonal symmetry. These regions are most likely Ga_xMn_1−xN, which produce the ferromagnetic contribution to the magnetization. In p-GaN implanted with Fe, the material after annealing showed ferromagnetic properties at temperatures that were dependent on the Fe dose, but were below 200 K in all cases. In these samples, TEM and diffraction analysis did not reveal any secondary phase formation. The results for the Fe implantation are similar to those reported for Fe doping during epitaxial growth of GaN.     

Abnormal junction profile of silicided p+/n shallowjunctions: a leakage mechanism

The leakage mechanism in p⁺/n shallow junctions fabricated using Co silicidation and shallow trench isolation processes has been investigated using transmission electron microscopy (TEM) combined with selective chemical etching. TEM and TSUPREM-4 simulation results show that dopant profiles bend upward near the edge of the active region. The formation of the abnormal profile is attributed to transient enhanced diffusion induced by source/drain implantation. Based on the TEM and simulation results, it is suggested that the shallower junctions formed near the active edge can serve as a source for leakage current in the silicided p+ /n shallow junctions     

Extended adaptive RBF equaliser for overcoming co-channelinterference

The authors investigate the problem of nonlinear adaptive equalisation in the presence of intersymbol interference, additive white Gaussian noise and co-channel interference. An extended radial basis function (RBF) network is proposed, in which regression weights are used in the output layer and the hidden unit is defined to have the Gaussian formula with the Mahalanobis distance. It is shown by simulation that the proposed structure gives reduced computational complexity without performance degradation, compared to that of the conventional RBF equaliser     

Robust backward adaptive formant prediction for speech coder

To improve the error performance of speech coders, an adaptation method for the backward adapted formant predictor is proposed. The filtered residual signal is used instead of the reconstructed output signal as the input to an adaptation of the formant predictor. The performance of the filtered-residual driven adaption method in the noise free channel is as good as that of conventional output driven adaptation. Moreover, the new adaptation method maintains the same robustness to channel errors as residual driven adaptation