Browsing by Subject "Gain measurement"

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    AlGaN/GaN HEMT-based fully monolithic X-band low noise amplifier
    (Wiley, 2005-04) Schwindt, R.; Kumar, V.; Aktas, O.; Lee, J. W.; Adesida, I.
    A fully monolithic AlGaN/GaN HEMT-based low noise amplifier is reported. The circuit demonstrated a noise figure of 3.5 dB, gain of -7.5 dB, input return loss of -7.5 dB, and output return loss of -15 dB at 8.5 GHz. The dc characteristics of individual 0.25-μm × 150-μm transistors were: maximum current density of 1.0 A/mm, maximum transconductance of 170 mS/mm and a threshold voltage of -6.8 V. The devices have a typical short circuit current gain cutoff frequency of 24.5 GHz and a maximum oscillating frequency of 48 GHz. The devices demonstrated a minimum noise figure of 1.6 dB with an associated gain of 10.6 dB at 10 GHz.
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    Bandwidth improvement in a cMUT array with mixed sized elements
    (IEEE, 2005-09) Bayram, Can; Olcum, Selim; Şenlik, Muhammed N.; Atalar, Abdullah
    A capacitive micromachined ultrasonic transducer (cMUT) is typically fabricated by concatenation of several cMUT cells with identical physical dimensions. If the membrane thickness is kept fixed, the radius of the cMUT determines the center frequency of operation. A smaller radius implies a greater center frequency. Therefore, it should be possible to put cMUTs with different sizes in parallel to get a larger bandwidth at the expense of gain. In this study, we investigate the optimization of the bandwidth characteristics of a cMUT by using mixed size cells. We designed two mixed size cMUT arrays with a predicted optimized fractional bandwidth value of about 155% at 5.4 MHz, and 146% at 8.8 MHz. These values are about 55% and 58% better than what can be achieved with a uniform size array at the corresponding center frequencies. There is almost no loss in the gain bandwidth product when two different sized cMUTs are used in parallel. There is about 9% increase in gain bandwidth product when three different sized cMUTs are used in parallel. It is shown, in this study, that gain bandwidth product and bandwidth can be enhanced by use of mixed size cMUT cells. © 2005 IEEE.
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    Design charts to maximize the gain-bandwidth product of capacitive micromachined ultrasonic transducers
    (IEEE, 2005) Ölçüm, Selim; Şenlik, Muhammed Niyazi; Bayram, Can; Atalar, Abdullah
    In this work we define a performance measure for capacitive micromachined ultrasonic transducers (cMUT) in the form of a gain-bandwidth product to investigate the conditions that optimize the gain and bandwidth with respect to device dimensions, electrode size and electrical termination resistance. For the transmit mode, we define the figure of merit as the pressure-bandwidth product. Fully-metallized membranes achieve a higher pressure-bandwidth product compared to partially metallized ones. It is shown that the bandwidth is not affected by the electrode size in the transmit mode. In the receive mode, we define the figure of merit as the gain-bandwidth product. We show in this case that the figure of merit can be maximized by optimizing the electrode radius. We present normalized charts for designing an optimum cMUT cell at the desired frequency with a given bandwidth for transmit or receive modes. The effect of spurious capacitance and liquid loading effect are considered. Design examples are given to clarify the use of these charts.
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    Integral action based Dirichlet boundary control of Burgers equation
    (IEEE, 2003) Efe, M. Ö.; Özbay, Hitay
    Modeling and boundary control for Burgers Equation is studied in this paper. Modeling has been done via processing of numerical observations through singular value decomposition with Galerkin projection. This results in a set of spatial basis functions together with a set of Ordinary Differential Equations (ODEs) describing the temporal evolution. Since the dynamics described by Burgers equation is nonlinear, the corresponding reduced order dynamics turn out to be nonlinear. The presented analysis explains how boundary condition appears as a control input in the ODEs. The controller design is based on the linearization of the dynamic model. It has been demonstrated that an integral controller, whose gain is a function of the spatial variable, is sufficient to observe reasonably high tracking performance with a high degree of robustness.