Sharif Digital Repository

We present a complete top-down design of a low-power multi-channel clock recovery circuit based on gated current-controlled oscillators. The flow includes several tools and methods used to specify block constraints, to design and verify the topology down to the transistor level, as well as to achieve a power consumption as low as 5mW/Gbit/s. Statistical simulation is used to estimate the achievable bit error rate in presence of phase and frequency errors and to prove the feasibility of the concept. VHDL modeling provides extensive verification of the topology. Thermal noise modeling based on well-known concepts delivers design parameters for the device sizing and biasing. We present two... 

In many radar and EW applications, after some processing, the envelope of the received pulse is calculated and is used for target detection. Most of the time only the effect of thermal noise is considered in such detectors, but in most of the practical applications, before envelope detection, the signal should be down converted from radio frequency (RF) to an intermediate frequency (IF). In this case, the phase noise of the local oscillator will affect the signal, too. Surprisingly, in contrast to thermal noise, the effect of phase noise on the envelope of signal becomes more considerable whenever the IF bandwidth is decreased. So there exists an optimum IF bandwidth for the receiver. In... 

In this paper, a spectral-phase-encoded ultrashort light pulse optical code division multiple access (SPE-OCDMA) system employing a novel nonlinear power-cubic optical preprocessor at its receiver's front end is theoretically investigated. The system's mathematical model and the statistical distribution of the decision variable Y, prior to the decision module of the receiver, are discussed. The first three moments of the random decision variable Y are obtained in the context of the above OCDMA system and subsequently used in an appropriate Log-Pearson type 3 (LP3) distribution to represent the random decision variable $Y$. Multiple access interference (MAI) and amplified spontaneous emission... 

Thermal noise is one of the most important limiting factors on the performance of switched-capacitor (SC) circuit due to the aliasing effect of wide-band thermal noise. In this paper a new simple method for estimating the effect of thermal noise is presented. In the proposed technique only the discrete sampled noise is considered. HSPICE simulator and analytical analysis are used to estimate the sampled noise specification on each clock state. Next, using difference equations of the circuit, time domain simulation is done by MATLAB. Based on this method, a SC integrator is analyzed and results compared to the measured noise response  

A novel N-path filter using a complex impedance is designed to replace the frontend SAW filters in receivers with on-chip bandpass filters. It is demonstrated that the center frequency of the filter can be tuned solely by changing the value of some capacitances without the need to change the clock frequency. In addition, thanks to the use of smaller capacitors, the silicon area is reduced compared to similar designs. The high-Q bandpass filter is realized utilizing two gyrators and an arrangement of four baseband capacitors with NMOS switches, driven by 4-phase 25% duty cycle clock signals. This paper also analyzes the performance of the proposed filter against imperfections such as thermal... 

The effect of thermal noise and avalanche photodiode (APD) noise in a code division multiple access (CDMA) system using generalized optical orthogonal codes (GOOC) are investigated for the first time. The modulations used are pulse position modulation (PPM) and overlapping PPM (OPPM). Double optical hardlimiter receiver structure is selected because of its efficient performance. We show that, in a system with all mentioned noise sources, known parameter values, and a bit error rate of 10-7, GOOC codes with cross correlation (λ) equal to 2 support 20 more users compared to strict OOC. We have also analyzed the spectral efficiency of the GOOC OPPM system and compared it with GOOC PPM. The... 

In this paper, the authors study the performance of a two-photon absorption (TPA) receiver in a typical communication system employing an optical amplifier. For the study, the authors develop a comprehensive performance analysis, taking into account noises due to an optical amplifier, shot noise, and thermal noise, using Gaussian approximation technique. In evaluating the performance of the system using this technique, the mean and the variance of the received signal will be derived. Comparing the results of receivers using the TPA process with that of a typical single-photon absorption (SPA) structure leads the authors to conclude that TPA receivers can be used when the speed of the... 

This paper describes a study of the performance of various configurations for placing multiple optical amplifiers in a typical coherent ultrashort light pulse code-division multiple access (CULP-CDMA) communication system using the additive noise model. For this study, a comprehensive performance analysis was developed that takes into account multiple-access noise, noise due to optical amplifiers, and thermal noise using the saddle-point approximation technique. Prior to obtaining the overall system performance, the input/ output statistical models for different elements of the system such as encoders/decoders, star coupler, and optical amplifiers were obtained. Performance comparisons... 

A class of generalized optical orthogonal codes (OOCs), namely, frame time-hopping (FTH) patterns with an extremely large cardinality, are studied for implementing multirate and multiservice (MR/MS) optical CDMA (OCDMA) networks. Conventional MR/MS methods, namely variable spreading rate and parallel mapping, are considered. Using FTH patterns, the problem of low OOC code cardinality in conventional MR/MS schemes is removed. Moreover, several new multicode methods, using subcode concatenation scheme, are proposed for MR/MS OCDMA. The proposed multicode schemes present flexibility for supporting MR/MS applications such as lower implementation complexity and cost, less need for service... 

Thermal noise is one of the most important challenges in analogue integrated circuits design. This problem is more crucial in switched-capacitor (SC) filters due to the aliasing effect of wide-band thermal noise. In this article, a new simple method is proposed for estimating the power spectrum density of output thermal noise in SC filters, which have acceptable accuracy and short running time. In the proposed method, first using HSPICE simulator, accurate value of accumulated sampled noise on sampler capacitors in each clock state is achieved. Next, using difference equations of the SC filter, frequency response of the SC filter is shaped by time domain analysis. Based on the proposed... 

In this paper, we analyze the performance of code acquisition system in atmospheric optical code division multiple access (OCDMA) communications using optical orthogonal codes. Memory introduced by temporal correlation of optical fading process precludes us from using the Markov chain model for a code acquisition analysis. By considering this issue, we discuss how to extend the applicability of the Markov chain model to the atmospheric OCDMA communications. We analyze and compare the performance of correlator and chip level detector (CLD) structures in the acquisition system. In our analysis, we consider the effects of free space optical channel impairments, multiple access interference, and... 

In this paper, we present an analytical approach in obtaining the probability density function (pdf) of the random decision variable Y, which is formed at the output of the power-cubic all-optical nonlinear preprocessor followed by the photodetector, with applications in ultrafast optical time-division multiplexing and optical code-division multiple-access systems. Our approach can be used to accurately evaluate the performance of ultrafast pulse detection in the presence of Gaussian noise. Through rigorous Monte Carlo simulation, the accuracy of the widely used Gaussian approximation of decision variable Y is refuted. However, in this paper, we show that the so-called log-Pearson type-3...