مجله مهندسی برق و الکترونیک ایران
سال یکم شماره 2 (تابستان و پاییز 1383)

The capacity of a communication channel is determined by its bandwidth and signal-to-noise ratio. For a digital user, these parameters determine the bit rate and the probability of error and so affect the achievable quality of service. In the recent multimedia communication systems, bandwidth is still a limiting factor. Hence, effective video compression techniques are essential to reduce the amount of video data. The new H.264/AVC video coding standard jointly presented by the ITU-T and ISO/IEC experts groups has achieved a significant improvement in compression performance compared to the previous standards. It promises to deliver good quality of video at low bit rates. However implies a need for useful operation of the video compression algorithms in error prone environments. This article presents an overview of the H.264/AVC features if the probability of error is more than normal values, receiving the correct data is not guaranteed. This in terms of video compression techniques and error resilient coding. Some simulation results are provided to demonstrate the efficiency of thecodec.

Speech signal enhancement is frequently referred to as a preprocessing step to speech recognition. However, in practice, this cannot be easily accomplished since the front-end signal processing techniques and/or parameters used in these two frequently differ. We apply a signal processing technique successfully used in speech enhancement to speech recognition and show that it can perform equally well compared to well-known speech recognition front-ends such as MFCC. The technique, oversampled filterbank analysis/synthesis throughweighted overlap add (WOLA), has been tested and performed satisfactorily on the TI-46 and Aurora tasks in both clean and noisy conditions and also in subbandspeech recognition. The results indicate the capability of this technique in reducing the front-end signal processing blocks of enhancement and recognition into a single block.

A method is presented for position control of a permanent magnet synchronous motor (PMSM). First a linear descretized state-space model of a PMSM with unknown parameters is identified; the identified model is then controlled using state feedback with integrator techniques. The simulation results of a typical motor are obtained and the influence of pole placement, noise and load variations is studied. Finally, simulation results are confirmed with experimental results.

— In this paper successful silicon wafer bonding technology using gold-silicon eutectic is reported. The wafers, device wafer and cap wafer are bonded in vacuum. Device wafer is terminated on the surface with a bond layer that can be single crystal silicon, a layer of polysilicon, gold or any other suitable metal, dielectric or semiconductor layer, and the cap wafer contains an electroplated gold bond ring. Bonding has been carried out in a standard wafer bonder by performing a pre-bake at 300°C and then pressing the wafers together by 1Mpa and subsequent bonding at a temperature of about 400°C for 30 minutes. Bonding yield of more than 95% is achieved on 4” silicon wafers with excellent reproducibility. Excellent coverage of soft eutectic bonding over non-planar surfaces has been investigated using 1.2mm-thick insulated feedthroughs of polysilicon, which shows a good flow of eutectic material over the feedthroughs. Thin film polysilicon diaphragm (~2.5mm-thick) and micro-Pirani gauge have been used to monitor and measure the low-pressure inside the packaged vacuum cavity. It is more than one year that we are monitoring the pressure by the amount of buckling in the diaphragm, and so far no pressure drop is observed. Direct pressure measurement is also underway by the vacuum packaged floating Pirani gauges fabricated inside the device wafer. It also has been shown that polysilicon is a better source material in gold- silicon eutectic formation as it bonds at relatively lower temperature than single crystal silicon.

This paper presents a detailed circuit analysis and PWM implementation of a fuel cell based Z-source converter using L and C components. The Zsource converter uses the shoot-through that simultaneously turns on both power switches in a leg in order to boost a DC-link voltage. A discrete time statespace model of the Z-source converter is given for DSP implementation. Also, a modified space vector pulse width modulation is described in detail for stepping upthe DC-link voltage and generating a sinusoidal AC output voltage. To verify the effectiveness of the analyzed circuit model and modified space vector PWMtechnique, simulation results using Matlab/Simulink will be presented under an open-loop control and a closedloop control.