Sharif Digital Repository

In this paper we use tunability of FBG to introduce a novel device for optically reading, writing or modifying the low-speed label(s). We utilize tunable FBG arrays as concurrent label modulating (multiplexing) elements. This second-level intensity modulation is used to send signaling messages between nodes of WDM networks. The fiber optic small-signal modulator is formulated, and its behavior is compared with the published reports  

A new single-bit cascaded 2-2 σ/δ (Sigma-Delta) modulator with only two op-amps, instead of four ones in conventional modulators, to decrease the static power consumption and area, is designed for GSM transceiver applications. The circuit consists of two new single op-amp, second-order, and low-pass loop filters to achieve a fourth-order quantization noise shaping. The modulator shows 84dB DR (Dynamic Range) for GSM signal bandwidth, while consuming 2.3mW from a 2.5V supply voltage. © 2003 IEEE  

A new second order sigma delta modulator with the reduced number of op-amps, to decrease static power consumption and area, is presented for voice band applications such as codecs. This switched capacitor modulator uses reused capacitor technique to reduce the input thermal noise and circuit area. It improves the DR of modulator by almost 0.5 bit. The modulator shows 87 dB DR for voice band while consuming 125 μW from a 2.5 V supply. © 2003 IEEE  

A single-chip Integrated circuit of 3.3 V/1 W class-D high fidelity and high efficiency audio power amplifier is presented in this paper. The design has been done using a 3.3 V/0.25 /spl mu/m CMOS process. The maximum output power is 1 W before the amplifier saturates. The THD+N at 0.5 W output power is below 0.03% and efficiency is better than 90% thanks to the careful design of the output stage. The dynamic range is more than 100 dB suitable for high fidelity audio applications. A single-loop single-bit third order sigma-delta modulator is used to generate the PWM signal from input audio signal. The PWM signal is then filtered at the output with a second order low pass filter external to... 

We investigate the possibility of frequency conversion in time-varying metasurfaces, composed of graphene microribbon arrays (GMRAs) with time-periodic modulation of their conductivity. We present a quasi-static model for the interaction of light with a temporally modulated metasurface, as well as an accurate analytical treatment of the problem of time-varying GMRAs. Results coming from numerical simulations are also available. We provide corrections to a previous related proposal for frequency conversion and refute the possibility of attaining frequency shifts not equal to an integral multiple of modulation frequency. Contrary to the preceding results, our findings show that efficient... 

In this study, the authors study a fibre-optic local area network deploying optical code division multiple access technique with differential M-ary pulse position modulation (DPPM). The authors present the performance analysis of DPPM signalling using a double optical hardlimiter receiver structure considering the impairment caused by interference of other users. The analysis assumes a set of bit asynchronous transmitters employing generalised optical orthogonal codes for their DPPM signalling (GOOC-DPPM). Using mathematical analysis and simulations, the authors have demonstrated that GOOCDPPM improves both frame error probability and the maximum achievable network throughput compared with... 

Limitations imposed by the non-linearity of optical links, in the front end of a receiving array antenna, on the performance of a pulse compression radar are studied. Particularly linear frequency-modulated waveforms backscattered from a pair of targets are inspected. Inter-modulation and gain compression by noise are presented as two remarkable phenomena. For an interconnection of two dual-drive Mach-Zehnder modulators, the sensitivity of the compressed echo at the output of a matched filter receiver to certain tunable parameters is studied numerically. Finally, certain values of DC bias and phase shift between the modulators' electrodes are recommended  

A novel sturdy multi-stage noise-shaping sigma-delta modulator that cancels the first-stage quantisation error at the output of the modulator is presented. Since any stage of the modulator has unity signal transfer function, the modulator would be very robust to circuit non-idealities such as finite op-amp gain. Furthermore, the signal processing timing issue in the critical paths of the proposed topology has been relaxed due to shifting the delay of the last integrator to the feedback path of the modulator. Moreover, this topology can be implemented in the circuit level by a fewer active blocks. Therefore, it practically would be suitable for low-voltage and low-oversampling applications.... 

Design and operation of three different optical sensors based on the intensity modulation are reported in this article. These sensors are measuring absence or presence of any liquid and the measurement variable is refractive index and optical absorption. Reported devices can also check the presence of air bubbles in the liquid flow line. Performance of these sensors is tested as a liquid flow monitoring device while using different light sources. Sensor #1 uses a simple cell with the long transmitter and receiver optical fibers. Sensor #2 utilizes a small cell assembly that includes the short transmitter and receiver fibers. Sensor #3 employs a quartz flow cell with the direct light... 

Wireless Nano-scale Sensor Networks (WNSNs) are very simple and energy restricted networks that operate over terahertz band ranging from 0.1-10 THz, which faces significant molecular absorption noise and attenuation. Given these challenges, reliability, energy efficiency, and simplicity constitute the main criteria in designing communication protocols for WNSNs. Due to its simplicity and energy efficiency, carrier-less pulse based modulation is considered the best candidate for WNSNs. In this paper, we compare the performance of four different carrier-less modulations, PAM, OOK, PPM, and BPSK, in the context of WNSNs operating within the terahertz band. Our study shows that although BPSK is... 

Purpose - Digital Delta Sigma Modulator (DDSM) is used widely in electronic circuits including Radars, class-D power amplifiers and fractional frequency synthesizers. The purpose of this paper is to propose an implementation for MASH DDSMs named as Multi Modulus Reduced Complexity (MMRC) architecture. Design/methodology/approach - This architecture will use a very simple pseudorandom Linear Feedback Shift Register (LFSR) dither signal with period N-d to randomize the digital MMRC modulator used for fractional frequency synthesizers. Using error masking methodology, the MMRC modulator can decrease the hardware consumption and increase accuracy of the fractional frequency synthesizer. Rules... 

This Paper presents a practical way to improve signal bandwidth and resolution in a Sturdy Multi-Stage Noise- Shaping (SMASH) sigma delta modulator. In this way, the processing timing issue in the critical paths of the proposed architecture has been relaxed due to the shifting delay of the modulator loop filter of each stage to the its feedback path. The proposed Unity-STF SMASH architecture, which is realized with several efficient techniques, would be robust to circuit non-idealities such as finite op-amp DC gain. Furthermore the topology can be implemented by a fewer active blocks, suitable it for low power, high operation speed applications. © 2006-2017 Asian Research Publishing Network... 

In this paper we investigate the active impedance of Time Modulated Array (TMA) as a low-cost and simple beamforming architecture. Since the antenna elements in TMA are periodically turned on and off, the active impedance of this structure has less variation compared to a phased array architecture. In this paper, we have compared the active impedance of a TMA structure and that of the phased array for different cases. The active reflection coefficient of the TMA is always below-10 dB, while the impedance of the phased array becomes unmatched for certain scan angles  

In this paper, a new method for automatic cancellation of mismatch-induced errors in folding ADC is introduced. Using "Trimmable MOSFET's" for input transistors, this method results in considerable reduction of the size of speed-determining transistors while keeping integral non-linearity (INL) arbitrarily low. Using this technique, an 8-bit folding ADC is re-designed and its performance is compared to the original work.©2005 IEEE  

In this paper, we propose an efficient method for demodulating pulse position modulation (PPM) signals based on Reed-Solomon decoding algorithm. It is shown that the proposed technique outperforms other demodulating methods such as those based on Lagrange, Spline, and Iterative algorithms. Furthermore, the proposed method is generalized to the case that the PPM signal is corrupted by additive white Gaussian noise. © 2004 Elsevier B.V. All rights reserved  

In this paper, the effect of two-dimensional electron plasma formed on the surface of a semiconductor on the refraction phase of an optical beam is investigated. Both the density and effective mass of the surface state electrons can be controlled by a transverse electric field. While the surface density of electrons varies slowly with the applied field, their effective mass changes instantaneously. Therefore, a high bandwidth for the phase modulation can be obtained. It is expected that the device operates in the far-infrared region with a semiconductor as the base material. GaAs is one of the best candidates having both large dynamic range, and large ratio of free electron to the crystal... 

Using certain Clifford modules, we give a method for constructing many examples of homogeneous Einstein spaces with negative scalar curvature  

In several recent papers, layered waveguide structures with conductive interfaces have been discussed, whose propagation properties are controlled by a transverse voltage. These structures can be used as a dynamic optical read/write memory cell, and programmable optical diffractive element. In this paper, the excitation of surface waves with the presence of interface charges is discussed. Interface charges affect the dispersion of surface waves, and therefore they can be used in various applications such as optical modulators, switches, sensors and filters. These waves can be superior to surface plasmon waves since they are not lossy. The lossless property is satisfied in limited range:... 

The feasibility of an integrated optical memory is explored. This memory cell is based on the plasma wave modulator/switch1, which has a horizontal layered structure. A transverse voltage maintains a bias for the structure and can be used for electrical write cycle. The cell content is then read by a propagating guided optical wave across the structure. It is also possible to apply full optical read/write/clear cycles as discussed. The read cycle can be either destructive or nondestructive, depending on the wavelength. A modification of this device may be considered as an opto-transistor, in which an optical signal controls the flow of another optical beam  

In this paper we examine the transmission of two types of ultra-wideband (UWB) signals, multiband orthogonal frequency division multiplexing (MB-OFDM) and impulse radio ultra-wideband (IR-UWB), over single mode fiber at 1550 nm. In order to investigate the impact of optical components such as laser diode, external modulator and single mode fiber on UWB signals, we develop mathematical models for these components. These models are experimentally verified and corresponding numerical parameter values are obtained by experiment. Using these models we discuss the transmission of two types of UWB signals over single mode fiber. A new figure of merit namely distortion factor is defined. Using...