Shahrokh Ahmadi

George Washington University, Washington, D. C., DC, United States

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Publications (10)0 Total impact

  • Akhil Gupta, Shahrokh Ahmadi, Mona E. Zaghloul
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    ABSTRACT: The past few years has seen a tremendous amount of work being published in the area of continuous-time delta-sigma ADC designs with various compensation techniques to counter its susceptibility to non-idealities like clock jitter and excess loop delay, to name a few. The focus of this paper is the design of a tunable continuous time bandpass delta-sigma modulator that utilizes an excess loop delay compensation technique proposed in (1) to optimize the SNR of the modulator, besides preserving its stability by incorporating a full clock cycle delay. An improved, low noise, compact gyrator-C structure is proposed to obtain a high-Q bandpass filter subsequently used in the design of a second-order bandpass delta-sigma modulator clocked at 400 MHz for direct conversion of narrow band signals around 100 MHz. The proposed structure eliminates the need of a capacitor bank/array for the coarse tuning of the modulator since this structure enables coarse tuning in the range of 80 to 120 MHz and fine tuning of 5 MHz above or below the centre frequency. This modulator has been implemented in AMI 0.5µ CMOS process and achieves an SNR of 46 dB over a bandwidth of 1 MHz, calculated from post-layout simulations. The power consumption of this design is 49 mW at a supply of 3V.
    International Symposium on Circuits and Systems (ISCAS 2011), May 15-19 2011, Rio de Janeiro, Brazil; 01/2011
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    ABSTRACT: The development of a shear horizontal surface acoustic wave (SH-SAW) liquid sensor with identification (ID) for wireless applications is described. Moreover, a novel feature of "write capability" for this sensor is proposed. The SH-SAW passive sensor has a delay line configuration with a sensing area. The sensor is fabricated on a lithium tantalate (LiTaO3) substrate, which is Y-cut with rotations specified between about 36° around the X-axis. The principle of detection is based on the attenuation and time delay between the signals. The sensor is encoded according to partial reflections of an interrogation signal by metal reflectors placed on both side of the interdigital transducers (IDT). The structure of the sensor, the principle of the wireless communication, the detection process and testing results are presented.
    International Symposium on Circuits and Systems (ISCAS 2010), May 30 - June 2, 2010, Paris, France; 01/2010
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    ABSTRACT: In this paper we describe the design and implementation of a CMOS surface acoustic wave (SAW) oscillator. The oscillator utilizes surface acoustic wave resonators implemented in both 1.6micron and 0.5micron AMI CMOS process and fabricated through MOSIS. When connected to Pierce oscillator circuits, these resonators are capable of synthesizing frequencies in the range of 400MHz to 1GHz. This paper also addresses the design issues involving codesigning micromachined resonators with CMOS circuitry to optimize the oscillator design
    01/2005;
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    ABSTRACT: ZnO, a well-known piezoelectric material, is used to develop micro-scale surface acoustic wave (SAW) delay line sensor. In this work, SAW delay line sensors are fabricated employing ZnO films that are deposited by RF sputtering technique. Films are characterized prior to device fabrication by X-ray diffraction (XRD) for film crystalline quality, UV-visible transmission spectroscopy for optical characteristics, and atomic force microscopy (AFM) for surface morphology. Interdigital electrodes producing surface acoustic waves in the hundreds of MHz are developed by photolithography and metallization techniques. SAW delay line sensor device testing, measurement and characteristics on RF sputtered ZnO films are presented and compared.
    Circuits and Systems, 2003 IEEE 46th Midwest Symposium on; 01/2004
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    ABSTRACT: The development of inexpensive and miniaturized Surface Acoustics Wave (SAW) gas sensors that are highly selective and sensitive is described. These sensors are implemented with micro-electro-mechanical systems (MEMS) in CMOS technology. IDT equivalent circuit and model for SAW delay line is introduced. Simulation results are included for characterization and design of the sensor. In this paper we will describe the design and post-processing steps to implement SAW device in CMOS technology. Design parameters of this device were obtained using modeling equivalent circuit to characterize sensor. Two approaches were used in the design of the SAW gas sensor that will be discussed. A CMOS chip was fabricated using MOSIS. Thin film ZnO was grown on Silicon based die and its characterizations is presented.
    Sensors, 2003. Proceedings of IEEE; 11/2003
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    ABSTRACT: The development of inexpensive and miniaturized SAW gas sensors that are highly selective and sensitive is introduced. These sensors are implemented with micro-electro-mechanical systems (MEMS) in CMOS technology. Since the sensors are fabricated on a silicon substrate, additional signal processing circuitry can easily be integrated into the chip thereby readily providing functions such as multiplexing and analog-to-digital conversion that are needed for integration into a network.
    Circuits and Systems, 2003. ISCAS '03. Proceedings of the 2003 International Symposium on; 06/2003
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    ABSTRACT: ZnO, a well-known piezoelectric material, is used to develop micro-scale Surface Acoustic Wave (SAW) delay line sensor. In this work, SAW delay line Devices are fabricated employing ZnO films that are deposited by RF sputtering technique. Films are characterized prior to device fabrication by X-Ray Diffraction (XRD) for film crystalline quality, UV-visible transmission spectroscopy for optical characteristics, and Atomic Force Microscopy (AFM) for surface morphology. Interdigital electrodes producing surface acoustic waves in the hundreds of MHz are developed by photolithography and metalization techniques. SAW delay line device testing, measurement and characteristics on RF sputtered ZnO films are presented and compared.
    Materials Research Society; 06/2003
  • S. Ahmadi, M. Zaghloul
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    ABSTRACT: In this paper, a Fabry-Perot based spectrometer and some of its advantages and applications are discussed. The CMOS fabrication processing steps for a MEMS design of a Fabry-Perot and a companion photodiode are shown. This companion photodiode of Fabry-Perot converts the filtered light intensity into an electrical signal. A CMOS integrated circuit is designed for the signal conditioning and processing of photodiode electrical signal. Using the CMOS integrated circuit, the analog signal is converted into a digital form and is available in an 8-bit bus for further processing
    Circuits and Systems, 2001. ISCAS 2001. The 2001 IEEE International Symposium on; 06/2001
  • S. Ahmadi, M. Zaghloul
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    ABSTRACT: In this paper, a Fabry-Perot based optical smart sensor and some of its advantages and applications are discussed. Basics of optical sensors and tight intensity modulations, with regard to the smart sensor, are discussed. The CMOS/MEMS implementation and fabrication of a Fabry-Perot sensor and it's companion photodiode are shown. This companion photodiode of Fabry-Perot converts the filtered light intensity into an electrical signal. A CMOS integrated circuit is designed for the signal conditioning and processing of photodiode electrical signal. Using the CMOS integrated circuit, the analog signal is converted into a digital form and is available in an 8-bit bus for further processing
    Circuits and Systems, 2001. MWSCAS 2001. Proceedings of the 44th IEEE 2001 Midwest Symposium on; 02/2001
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    ABSTRACT: Mobility of the relay node in this analysis is initially restricted to straight line motion and results are obtained for all possible combinations of start and expiration points. This is followed by the analysis for piece-wise linear motion which may be considered as a sequence of straight lines in different directions at rapid succession. The paper is arranged in the following manner. Section II defines the energy cost function and lists the assumptions used in the model. Section III analyzes deterministic motion of the mobile node along a straight line motion, while Section IV approximates the deterministic motion as piece-wise linear segments. Finally, Section V concludes the paper with a discussion of future areas of work.