نشریه صنایع الکترونیک
سال سوم شماره 4 (پیاپی 11، زمستان 1391)

In this paper, a fourth-order delta-sigma modulator is designed and simulated. The presented architecture offers the possibility of implementation of a high-order deltasigma modulator with multi-bit quantizer without suffering from DAC nonlinearity or instability problems. The proposed modulator consists of two single-bit second-order delta-sigma modulators at the first and second stages and an 8-bit pipeline ADC at the last stage. Besides, a reduced sample rate structure is implemented for the proposed modulator, which eliminates a few digital filters, and reduces power dissipation.To prove the idea, both the 2-2-0 MASH delta-sigma-pipeline modulator and its reduced sample rate counterpart are simulated using MATLAB/SIMULINK. Finally, power estimation for the proposed ADC at the sampling frequency of 40MHz is presented.

A major goal of a spread spectrum communication system is to protect communication signals against interference and exploitation by unintended listeners. In fact, Low Probability of Detection and Low Probability of Intercept are two important parameters for increasing performance of the system. In DS-CDMA, these goals are reached by multiplying the data information and spreading sequences. Chaotic sequences, with its unique properties, have numerous applications in building spreading codes. Before, using one-dimensional Bernoulli sequence as spreading code is proposed. The main feature of this sequence is its negative autocorrelation at lag of one. Efficiency of the system based on these codes will be increased comparing with other known codes. On the other hand, employing the complex chaotic sequences as a spreading sequence also has been discussed in several papers. In this paper, the use of two-dimensional Bernoulli chaotic sequences as a spreading code is proposed. The quality of a multiuser synchronous and asynchronous DS-CDMA will be evaluated by applying these sequences in AWGN and fading channel. Simulation results indicate the improved performance compared with conventional spreading codes like Gold codes and also other similar complex spreading sequences.

According to various applications of variable capacitors in electrical devices, design and fabrication of them are well developed. However, reaching to variable capacitor with low drive voltage, short settling time, wide tuning range, smaller dimensions, and longer lifetime, simultaneously, are difficult yet. In this paper, to satisfy these constraints, particle swarm optimization (PSO) is used in designing MEMS capacitors. In spite of gradient based algorithms, PSO achieves the absolute optimized value. The design consists of modeling, simsulation, and optimization. In addition, a method is introduced to realize the calling of simulation analysis programs designed by ANSYS parametric design language (APDL) in MATLAB. This method is capable to design every microelectromechanical two plate capacitors with electrostatic actuation. The proposed design method is as follows: First, the desired amounts of parameters that are important for the designers such as maximum drive voltage, initial capacitance, and limitations of structure dimensions are fed to the program as inputs. Then, the program starts to design a structure of variable capacitor and sends out the optimized structure design. The simulation results show that tuning range of 50% is obtained with a lower actuation voltage than the other works.

In this paper a programmablecircuitis presentedfor generationPosicast pulse. In this scheme first, the original pulse is delayed, and then the original and delayed pulse isadded with adder circuit. In the presented delay circuit, delays at rising and falling edges are controlled with two different input code words. Also, in the presented adder circuit, the first levels of voltage at rising and falling edges are controlled with two different input code words. A programmable circuit for generation Posicast pulse is proposed with composition of delay and adder circuits. Our experimental results show that the proposed delay and adder circuits work linearly respects to the code word. Finally the output of the programmable circuit is applied on the RLC circuit, the average of overshoot reduction at rising and falling edges are 91.78% and 98.56%, respectively. Also, the average of settling time improvement in these edges is 70.7% and 90.47%, respectively.

One of the key components of a micro-sensor is the MEMS micro-heater. It has an extremely wide range of applications such as gas sensors, pressure sensors and so on. In this study, design and simulation of MEMS micro-heater is described. Heat transfer analysis and FEM simulation using ConvetorWare software were performed to determine the optimal design of micro-heater.The sensitivity and resolution of gas sensors that use a micro-hotplate are dependent on the temperature uniformity of the sensitive devicearea. There are several ways to create a uniform temperature distribution on a micro-heater. In this paper the modification of micro-heater geometry is the method used. Eight different heater geometries are simulated using ConvetorWare software to determine which geometry can give the most uniform temperature distribution. The simulations show that the heater geometry which Ω-shape results in the most uniform heat distribution.

In this paper, the source of errors are in phased array antennas are identified and some existing methods for solving these errors are introduced. In these methods the calibration process need to at least one source with known characteristics. Also the knowledge of source direction and the subsystems characteristics are required. In the proposed algorithm, there is no need to any of these data for updating the array weights. The only input of the algorithm is the received combined power from all channels. In this paper, the source of errors are in phased array antennas are identified and some existing methods for solving these errors are introduced. In these methods the calibration process need to at least one source with known characteristics. Also the knowledge of source direction and the subsystems characteristics are required. In the proposed algorithm, there is no need to any of these data for updating the array weights. The only input of the algorithm is the received combined power from all channels.