Ronald J. Pieper

Integrated Optical Sigma-Delta Modulators.

Abstract : Modern avionics equipment, such as super resolution direction-finding systems, now require resolutions on the order of 20 to 22 bits. Oversampled analog-to-digital converter architectures offer a means of exchanging resolution in time for that in amplitude and represent an attractive approach to implementing precision converters without the need for complex precision analog circuits. Using oversampling techniques based on sigma-delta modulation, a convenient tradeoff exists between sampling rate and resolution. One of the major advantages of integrated optics is the capability to efficiently couple wideband signals into the optical domain. Typically, sigma-delta processors require simple and relatively low-precision analog components and thus are well suited to integrated optical implementations. This thesis reviews the current sigma-delta methodology, the advantages of optical integrated circuits and presents the design of a second-order, integrated optical sigma-delta modulator. Simulation results for both a first and second order architecture are presented by evaluating the transfer characteristics numerically. Design parameters such as limit cycles are quantified and explained. Performance issues and future efforts are also considered. (AN)

Comprehensive analytical approach to predicting freeze-out and exhaustion for uniform single-impurity semiconductors in equilibrium

In this paper, a complete analytical description for an exact expression for temperature dependence of the majority carrier in a single-impurity, nondegenerately doped equilibrium semiconductor is proposed. Analysis establishes that the problem is solvable exactly by identifying the only physically possible root to a cubic equation. This solution is complemented by an iterative technique that identifies boundaries for the intrinsic, freeze-out, and exhaustion regimes and facilitates selecting a reasonable range of temperatures in which to display the exact solution. Similarly, an exact expression for the temperature-dependent Fermi level is obtained. Fairly simple tests and checks on the analytic results are explained and demonstrated. This model provides an attractive alternative or supplement to established classroom approaches for this topic usually covered in senior and first-year graduate-level solid-state courses in physics and electrical engineering.

Using PSpice to model the cooling performance of convective surfaces

The electronic circuit simulator PSpice can provide the means of obtaining numerical non-analytic solutions to thermal heat flow problems which would otherwise be difficult or impossible to derive. Rules for relating physical heat flow parameters to equivalent distributed lossy transmission line parameters are derived. This method for numerical evaluation of the heat dissipating performance of complicated fin structures forming cold-stacks is validated by comparison with previously published analytic solutions for double stack cold plates. Although the focus of the presentation is on the static, i.e. DC performance, the extension of this numerical simulation technique to transient problems in heat transfer of interconnected fin structures is clarified.

Observations on convergence problems of pipeline networks

Presented in the paper will be a brief introduction to methods of solving pipeline networks and the corresponding electrical analogies. Numerically generated data from a pipeline example will support the argument that two-cycle trapping is created by the nonlinearity in the pipeline network model in the transition fluid flow regime. Second the results will demonstrate that averaging between iteration cycles greatly facilitates the objective of reaching a convergent solution. Lastly, data generated from the one dimensional Feigenbaum model which replicate effects similar to the N-dimensional pipeline model will also be presented.

PASSIVE RANGE ESTIMATION USING DUAL-BASELINE TRIANGULATION

Modern combat systems based on active radar sensing suffer disadvantages against low-flying targets in cluttered backgrounds. Use of passive infrared sensors with these systems, either in cooperation or as an alternative, shows potential for improving target detection and declaration range for targets crossing the horizon. Realization of this potential requires fusion of target position data from dissimilar sensors, or passive sensor measurement of target range. The availability of passive sensors that can supply both range and bearing data on such targets would significantly extend the robustness of an integrated ship selfdefense system. We consider a new method of range determination with passive sensors based on the principle of triangulation, extending the principle to two orthogonal baselines. The performance of single or double baseline triangulation depends on sensor bearing precision and direction to target. An expression for maximum triangulation range at a required accuracy is derived as a function of polar angle relative to the center of the dual-baseline system. Limitations in the dual-baseline model due to the geometrically assessed horizon are also considered.

A VLSI implementation of a universal programmable low sensitivity sampled data filter

In this presentation, a CMOS custom Integrated Circuit featuring a multi-stage Universal Switched-Capacitor (SC) Filter is Introduced. The network is based on the Generalized Immittance Converter (GIC) configuration, known for its excellent passive and active sensitivities. CMOS switches were used for elements relocation and are digitally controlled to select and realized different filter topologies. Switches were also used to control banks of binary-weighted capacitors that determine the filter center frequency, quality factor as well as its order. The bilinear transformation were utilized in the SC implementation of the filter resistive elements. Extra care was considered in the design procedure to minimize the effect of stray capacitors on the network transfer functions. The result was a general purpose digitally programmable multi-stage network that can equally compete with the best available stray insensitive filter. The design also inherit the low active and passive sensitivities the GIC enjoys.

Circuit modeling to predict the performance of force-cooled cold plate structures

The electronic circuit simulator PSpice can provide the means of obtaining numerical nonanalytic solutions to thermal heat flow problems which would otherwise be difficult or impossible to derive. Rules for relating physical heat flow parameters to equivalent distributed lossy transmission line parameters are derived. This method for numerical evaluation of the heat dissipating performance of complicated fin structures forming cold-stacks is validated by comparison with recently published analytic solutions for double stack cold plates.

The Eikonal ray equations in optical fibers

The traditional methods for the characterization of ray trajectories in nonhomogeneous media are based on the Eikonal equation valid in the region of geometrical optics. To apply Eikonal theory to fiber optics requires a fairly extensive use of vector calculus and geometry. Alternatively, through a simple correspondence rule, and a few intuitive guidelines for relating rays to waves, an equivalent set of trajectory equations can be obtained. This approach results in the Eikonal equations for the space evolution of optical fiber rays which are expressed in terms of the mode analysis invariants, azimuthal mode number, and optical waveguide propagation phase constant.

Laboratory and computer tests for Carson's FM bandwidth rule

The commonly cited significance for Carsons FM bandwidth is that it defines spectral limits which contain 98% or more of the spectrum power. The 98% rule typically requires enough computations to discourage its application for in-situ laboratory type measurements. Furthermore, the 98% rule will only provide an upper bound for Carsons bandwidth rule. What is suggested in this paper is a more direct, simpler approach which provides both upper and lower bounds. The sideband reduction method described, is based on taking visual cues for sideband reduction levels measured with respect to the unmodulated carrier. Computations required by the method are not extensive. In addition, the sideband reduction method is confirmable using an FFT test on the computer.

Real-time histogram generation using optical scanning

A prototype of an optical-electronic histogram generator has been designed and tested for 1-D objects. In this scheme, the object to be analyzed is laser scanned. The resulting optical signal is detected by a photodetector which generates an electrical signal output which is subsequently analyzed with a combination of analog and digital electronics. The system has shown to be fairly modular in design. Various aspects of the extension of the design to two dimensions is discussed.<<ETX>>