نشریه مهندسی مخابرات جنوب
پیاپی 26 (زمستان 1396)

In this paper, the design and simulation of a transmission impedance amplifier using 0.18 µ CMOS technology for use in the amplifier section of optical telecommunication receivers are presented. The idea presented in this paper is based on the use of a parallel-parallel feedback structure with a cascade interest rate. This structure is quasi-differential and is designed to increase the allowable range of input power and prevent amplifier saturation, a circuit with a variable gain. The simulation results show a maximum gain of 64 dB, a bandwidth of 1.8 GHz, power consumption of 20mw, and a spectral intensity of the noise current referred to as the PA / 9 input. Also, by using variable gain control, the gain of the amplifier transmission impedance can be reduced to 46 dBΩ. The results indicate that the proposed design is very suitable for a 2.5 Gb / s optical telecommunication system.

Using 0.18 µm technology, CMOS transistors are designed as a VCO prototype. In the proposed VCO structure, an adjustable active inductor and a vector for the LC tank are used. The wide frequency regulation in this circuit is controlled by an adjustable active inductor and fine-tuning with a reactor.VCO with MOS vector in storage mode has the lowest power consumption and the lowest phase noise at large offset frequencies. The benefits of using MOS vectors increase significantly when more advanced CMOS technologies are selected. Due to the absence of passive elements, the fully integrated VCO takes up less chip surface area in the circuit.

In this article, the biological effects of high-frequency electromagnetic waves on the body are first investigated. Then the amount of specific absorption rate (SAR) and the factors affecting it are investigated and then the amount of SAR is simulated in the standard model IEC-66209 in which the head tissue and a reference antenna called Diple are modeled and the effect of changing physical parameters onSAR, such as tissue conductivity, tilt effect on the antenna, the effect of smaller size, the effect of distance from the antenna, change of SAR measurement location, and SAR level in human hands have been simulated and compared with the standard model. The simulations are all performed at 835 MHz (except for the effect of frequency change).

Multi-path propagation is one of the most important limiting factors for sending high bit rate information. It is possible to send high bit rates at frequencies in the GHz range, which is the biggest problem in this multi-channel propagation frequency band. OFDM technique is very resistant and efficient in dealing with the adverse effects of multipath propagation by dividing the sent symbols between several sub-carriers and sending them simultaneously. With the increasing growth of high-capacity systems, the applications of this technique are increasing day by day. The OFDM system along with CDMA is proposed for next-generation mobile networks. Channel coding plays a very important role in improving OFDM efficiency. Due to the special structure of OFDM, the use of channel coding in it has special features compared to single-carrier systems that increase the efficiency of the system. Hence, this system is also called coded OFDM or COFDM. In this paper, while studying the OFDM technique, the effect of the channel coding range on the efficiency of the OFDM system is investigated.

In this paper, an adaptive method based on carroll conversion is introduced to reduce spike noise. Speckle noise is a multiplicative impurity that in this paper we first convert to mass with a preprocessing step. An interest function is then introduced to threshold the Coralt coefficients, which has three general thresholds. An objective function, based on an estimated noise correlation with the edges of the output image, then provides the optimal parameters in the threshold of the interest function by searching with a general search algorithm called the particle swarm optimization algorithm. The appropriate objective function is then considered for the PSO algorithm search and the results of speckle reduction are measured by the Violet method.

MRI is one of the most useful imaging techniques today. Abdominal MRI imaging is widely used in medical diagnoses such as tumors, tissue diagnostics, etc. Therefore, fast and appropriate segmentation algorithms play an important role in diagnosing diseases, classifying and quantifying tissue, isolating different elements and diagnosing tumors. In this paper, an automatic spleen separation system from abdominal MRI images is presented, which includes two stages of preprocessing and spleen separation algorithm. Pre-processing is used to de-noise and improve image quality. Isolation of the spleen consists of three stages of segmentation using watershed conversion, calculation of features, and the final step of comparing these features with reference values. Any element whose properties are closer to the reference properties is labeled as a spleen. A forward neural network was used to obtain the reference values, which are the same as the shape of the spleen.  The results of the spleen output obtained are compared with the spleen output extracted by a specialist, and the percentage difference between the two outputs is considered as an error.