Current-Mode Temperature Compensated Continuous-Time CMOS Transconductance-C Filter

In this paper a low voltage low power current-mode continuous-timelow-pass filter is presented. The current-integrator is constructedof a multi-output linearized transconductance element drivenby a balanced transimpedance amplifier. A 1 MHz third order ellipticlow pass filter is designed and fabricated with the proposedcurrent-mode integrator. The measurements show capability ofoperation with down to a 3 V supply voltage. The measured currentconsumption is 850 µA at room temperature andthe dynamic range is 66 dB. The distortion of the filter is below50 dBc with peak signal levels up to twice the quiescent currentlevel and with the refined designs even lower distortion is expected.The filter uses a CMOS-current reference for temperature andprocess variation stabilization with a measured corner frequencytemperature coefficient of –100 ppm/K.     

Temperature compensated logarithmic peak detector

A temperature compensated logarithmic amplifier for signal strength indicator or automatic gain control applications is presented. The logarithmic function is realized with a current-feedback operational amplifier with a nonlinear diode feedback. The designed BiCMOS current-feedback operational amplifier utilizes a novel circuit topology which makes possible constant 1 MHz bandwidth amplification with closed loop voltage gains up to 60 dB. The offset current of the current-feedback amplifier is cancelled with an active OTA-C feedback loop. The logarithmically amplified signal is further processed by a peak detector and a temperature compensation circuit. The temperature compensation principle is based on a division of two v _BE:s and it is realized with a current controlled variable current mirror. The logarithmic amplifier is fabricated with a 1.2 micron BiCMOS-process with NPN's f_T of 7 GHz. The power consumption of the circuit is 25 mW with a 4.5 V supply voltage.     

Time-frequency distributions with complex argument

A distribution highly concentrated along the group delay or the instantaneous frequency (IF) is presented. It has been defined by introducing a signal with a complex argument in time-frequency (TF) analysis. Realization of a signal with a complex argument, using a signal with a real argument, is described. The reduced interference realization of the complex argument distribution, in the case of multicomponent signals, is presented. The proposed distribution is used for the IF estimation. It is shown that the estimation can be improved with respect to the Wigner distribution based one since the bias can be significantly reduced with only a slight increase of the variance. The theory is illustrated by examples     

The source coding game

The encoding of a source whose probability distribution varies arbitrarily from letter to letter is considered. The problem is formulated as a two-person statistical game. The exponential rate of growth with block length of the minimum number of codewords needed to achieve a specified fidelity with respect to a single-letter distortion measure is determined. The rate distortion function of a source whose statistics are entirely unknown is obtained as a special case. The dependence of the results on the rules under which the game is played also is studied. The analysis is based on a refinement of the usual random coding argument for sources which sheds new light on the significance of the term that decays at a doubly exponential rate with block length.     

Performance analysis for impulse radio and direct-sequence impulse radio in narrowband interference

The impact of narrowband interference (NBI) on two ultra wideband (UWB) systems is analyzed. The two systems are impulse radio (IR) and a variation of it, termed direct-sequence IR (DS-IR). The signal-to-noise ratio (SNR) at the decision device of a correlation receiver is computed for both systems, assuming that the NBI is wide sense stationary and that the channel is frequency-selective. The SNR is expressed by means of a simple equation involving the signal and the interference spectrum. Next, a statistical model for the interference is introduced, considering the interference as the sum of a given number of sinusoidal signals with random powers and frequencies. The bit-error rate of IR and DS-IR is derived. The results are then specialized and compared with simulations in three case studies of practical interest, where the NBI is a single jammer with deterministic power and frequency, a multitone signal with random frequencies, or a grid of interfering signals with random powers.     

Determination of the effective permittivity of a body in a waveguide from the reflection coefficient

The inverse problem of diffraction of the electromagnetic field by an inhomogeneous body placed in a rectangular waveguide with perfectly conducting walls is considered. The problem is reduced to a nonlinear volume singular integral equation. The integral equation is solved with the help of the iteration method. The permittivity is determined with the use of the reflection coefficient. Computation results for a figure of a complex shape are presented.     

Applications of universal context modeling to lossless compressionof gray-scale images

Inspired by theoretical results on universal modeling, a general framework for sequential modeling of gray-scale images is proposed and applied to lossless compression. The model is based on stochastic complexity considerations and is implemented with a tree structure. It is efficiently estimated by a modification of the universal algorithm context. Several variants of the algorithm are described. The sequential, lossless compression schemes obtained when the context modeler is used with an arithmetic coder are tested with a representative set of gray-scale images. The compression ratios are compared with those obtained with state-of-the-art algorithms available in the literature, with the results of the comparison consistently favoring the proposed approach.     

Analysis and design of clamped-mode resonant converters withvariable load

In this paper, a design procedure for clamped-mode resonant converters working with variable load is proposed and analyzed. The operation of these converters with general parallel or series loads is reviewed first. The operation of the transistors as zero-voltage switches is identified and characterized as mode A. Mode A is preferred to simplify the implementation of the power switches and to increment the converter efficiency. As a case study, the design of an RF power amplifier is presented. The amplifier is connected to a variable load with reactive characteristics, through a low-pass filter of three elements. The validity of the proposed design approach is verified with an experimental setup     

s̱-expected busy period of the service facility of a 1-server n-unit system subject to arbitrary failure and different repair strategies

This paper deals with the s?-expected busy period of a n-unit system with a single repair facility. The service facility is called for whenever r (1 ≤ r ≤ n) units are in failed condition and is retained until no unit is waiting for repair. The analysis is carried out under the assumption that the time to failure of a unit is arbitrarily distributed while the service rate is constant. The case when n = 2 with the failure time distribution is 2-stage Erlangian is discussed.     

210-320 GHz Multi-Hole Directional Coupler Design and Measurement

The design of a 210-320 GHz multi-hole directional coupler is described. The coupler performance is measured with a millimeter vector analyser across the band 205-350 GHz and compared with simulations. The coupler consists of two waveguides whose broad walls are separated by a thin metal sheet with an array of circular holes according to a Chebyshev distribution of couplings. The coupling is 11 dB with a typical variation of ± 2dB across the WR3 band and the isolation is more than 25 dB.     

A 64 kbit/s Videophone codec with forward analysis and control

A new combination of coding methods for a 64 kbit/s transmission system for typical videophone situations is investigated. The codec structure is based on a standard hybrid discrete cosine transform (DCT) codec with temporal prediction. The picture is divided blockwise into changed and unchanged areas. One motion vector with subpel accuracy is computed and transmitted for each block of the changed area. For the forward analysis, the prediction error is calculated in the whole picture. Only the blocks with the highest prediction errors are updated by a DCT with a perception adaptive quantization. The number of DCT update blocks depends on the remaining bits after the transmission of the overhead information. The codec is controlled by a forward analysis of the prediction error and is not based on a buffer control. The spatial resolution of the source signal is reduced in two steps to prevent a codec overload caused by too much activity between two frames.     

The Measurement of Noise in Microwave Transmitters

A tutorial review of the basis for transmitter noise measurements shows that noise is best described and measured as AM and FM noise. The determination of RF spectrum is done by calculation after the AM and FM noise are known. The contribution of AM noise to RF spectrum shape is determined by the power spectral density shape of the AM noise. The contribution of FM noise to RF spectrum is to make the shape that of an RLC circuit resonant response rather than a delta function with a sideband structure. The measurement of AM noise is done with a direct detector diode. The measurement of FM noise for frequencies above 5 GHz is done with a discriminator based on a one-port cavity resonator. The measurement of FM noise below 5 GHz is done with an improved transmission line discriminator which is described in detail. Measurement of low-power low-noise signal sources is made posbible with an injection-locked oscillator for a preamplifier to the discriminator. The most widely used baseband analyzer is the constant bandwidth superhetdrodyne wave or spectrum analyzer. Most differences in measurement results are resolved by understanding the baseband analyzers. At least the baseband spectrum analysis of transmitter noise measurements can be automated with worthwhile savings in time and improvement of documentation.     

Reradiation (echo) analysis of a tapered tower section supporting aside-mounted DTV broadcast antenna and the corresponding azimuth pattern

Reradiation from a non-vertical obstruction such as a tapered section of a broadcast antenna supporting tower is analyzed. The reradiation takes on the form of a cone, which is symmetrical about the tower leg axis, modified by the reflection coefficient that varies with azimuth. The reradiation is directed either above the horizon where it is lost or below the horizon where it interferes as an echo with the direct radiation. The reradiation has an elevation pattern which is a replica of the transmitting antenna elevation pattern, but is redirected by the nonvertical tower leg. The reradiation combines with the direct radiation to form an azimuth pattern which varies with distance from the broadcast antenna. The reradiation, being an echo, is analyzed for multipath distortion of the VSB pulse. It is shown that the impact on DTV receiver threshold is minimal     

An analysis of DTV propagation into and within a room in a domesticenvironment

A window in a room within a domestic environment in a structure with aluminum siding is analyzed with respect to its radiating properties. The window is modeled as a rectangular aperture, which diffracts the distant horizontally polarized signal from a DTV transmitting antenna into the environment of the room. The diffraction signal, also horizontally-polarized, is combined with the distant signal, which penetrates the aluminum siding at some loss, and thereby a field distribution within the room is created. The window-diffracted signal is almost entirely a near field (Fresnel zone) within the room while the distant field is a far field (Fraunhofer zone) within the room. Various locations within the room are examined with respect to echoes, with and without scattering (human) bodies. A receiving antenna is positioned at the locations examined     

Complexity reduction of digital filters using shift inclusive differential coefficients

We present a graph theoretical methodology that reduces the implementation complexity of the multiplication of a constant vector and a scalar. The complexity of implementation is defined as the required amount of computations like additions. The proposed approach is called minimally redundant parallel (MRP) optimization and is mainly presented in a finite impulse response (FIR) filtering framework to obtain a low-complexity multiplierless implementation. The key idea is to expand the design space using shift inclusive differential coefficients (SIDCs) together with computation reordering using a graph theoretic approach to obtain maximal computation sharing. The problem is formulated using a graph in which vertices and edges represent coefficients and computational cost (number of resources). The multiplierless solution is obtained by solving a set cover problem on the vertices in the graph. A simple polynomial run time algorithm based on a greedy approach is presented. The proposed approach is compared with common-subexpression elimination to show slightly better results and is combined with it for further reduction of complexity. Simulation results show that 50-60% complexity reduction is achieved by only applying the MRP algorithm, and 70% complexity reduction is obtainable by combining it with common-subexpression elimination under a delay constraint of two or three.     

A Stability Analysis for Time-Domain Method-of-Moments Analysis of 1-D Double-Negative Transmission Lines

The stability of time-domain simulations is examined for a generalized lossy double-negative transmission line (TL). This is accomplished using a "modified" version of the Courant-Friedrichs-Lewy stability criterion. The time-domain simulation is implemented using a method-of-moments formulation with the generalized TL equations. An analytic expression is derived by combining the Z-transform with von Neumann methods. The credibility of simulated time-domain results is verified through comparison with modal behavior determined using a frequency-domain treatment for a periodic structure.     

Small circularly polarised folded patch antenna

A small circularly polarised (CP) patch antenna with dual T-shaped probe feeds is presented. The patch is folded like a cap to generate a CP wave as well as to reduce the size of the antenna. The proposed antenna is operated at the centre frequency of 2.28 GHz with circular polarisation. The impedance bandwidth (SWR<2) is 21.8% from 2 to 2.49 GHz and the axial ratio bandwidth (AR<3 dB) is 3.5%. The measured gain is around 7.5 dBi. The antenna shows a good CP performance with a symmetric radiation pattern. The total area of reduction is 54% in comparison with the conventional half-wave patch antenna.     

Field distribution in a circular waveguide with a corrugateddielectric lining

The problem of wave propagation through a circular cylinder with a periodically interrupted dielectric lining is solved by a boundary value approach by considering the region between the corrugations as a medium with a tensor permittivity. The characteristic equation for the phase constant is derived by matching the field components. Solutions for the phase constant are obtained and the variation of the phase constant with the physical parameters is studied. The variation of the axial and circumferential electric field components in the transverse plane is also studied     

A novel efficient algorithm for scattering from a complex BOR usingmixed finite elements and cylindrical PML

An efficient finite-element method (FEM) is developed to compute scattering from a complex body of revolution (BOR). The BOR is composed of a perfect conductor and impedance surfaces and arbitrary inhomogeneous materials. The method uses edge-based vector basis functions to expand the transverse field components and node-based scalar basis functions to expand the angular component. The use of vector basis functions eliminates the problem of spurious solutions suffered by other three component FEM formulations. The FEM mesh is truncated with a perfectly matched layer (PML) in cylindrical coordinates. The use of PML in cylindrical coordinates avoids the wasted computation which results from a spherical mesh boundary with an elongated scatterer. The FEM equations are solved by ordering the unknowns with a reverse Cuthill-McKee algorithm and applying a banded-matrix solution algorithm. The method is capable of handling large, realistic radar targets, and good agreement with measured results is achieved for benchmark targets     

Linear motor motion control using a learning feedforward controller

The design and realization of an online learning motion controller for a linear motor is presented, and its usefulness is evaluated. The controller consists of two components: (1) a model-based feedback component, and (2) a learning feedforward component. The feedback component is designed on the basis of a simple second-order linear model, which is known to have structural errors. In the design, an emphasis is placed on robustness. The learning feedforward component is a neural-network-based controller, comprised of a one-hidden-layer structure with second-order B-spline basis functions. Simulations and experimental evaluations show that, with little effort, a high-performance motion system can be obtained with this approach