Katarzyna Opalska

Lumped circuit model of RF amplifier for SPICE simulator

The paper presents the lumped model of RF amplifier for the generic SPICE circuit simulator. Model is constructed on the basis of measured s-parameter data set of the amplifier. Data – transformed to admittance (y) domain - is approximated by rational functions, which later are synthesized as RLC (sub)circuits. Final amplifier model - obtained by representing Y matrix of two-port circuit by the set of passive components and controlled voltage/current sources – is shown to be equivalent to the original s-based model and may be used in any generic circuit simulator.

Analysis of some basic properties of multicavity photoacoustic Helmholtz cells

The paper presents results of comparative analysis of some basic properties of multicavity photoacoustic Helmholtz cells. The analysed cells were three-cavity Helmholtz resonators formed from a standard dual-cavity photoacoustic Helmholtz cell with an additional cavity connected by means of a capillary with the sample cavity of the cell at the other end. Influence of change of the volume of the additional cavity as well as diameter and length of the connecting duct on the microphone signal vs. frequency was studied. Analysis was based on computer simulations in which a modified transmission line model was used. The model was improved by introducing of additional damping factors which values were extracted from measurements of number of practically implemented dual-cavity photoacoustic Helmholtz cells. The analysis showed that additional cavity makes it possible to improve shape of the frequency response of the cell. In particular it is possible to extend range of frequencies in which resonance properties of the cell can be used for the purpose of photoacoustic signal amplification. It should be noticed that choice of the cell dimensions must be careful, as some combinations decrease resonance properties of the cell.

Generation of parameterized macromodels of two-port RF circuits for SPICE simulator

This paper presents a three step procedure for creating a small signal parameterized circuit model of a two-port RF module characterized in frequency domain. First, Vector Fitting is used to find rational approximation of Y matrix entries. Second, RLC equivalent circuits are synthesized for each approximation and complimented with the controlled sources. Finally the RLC components are parameterized with operating conditions of the original two-port module. The procedure is illustrated for the case of an RF amplifier for which the generated model is shown to be useful for the small signal SPICE analysis both in frequency and time domain.

Influence of skin-effect on TDR-based diagnosis of transmission line

The paper illustrates an essential influence of skin effect on results of time-domain reflectometry technique applied to diagnosis of DSL transmission line. Skin effect (frequency-dependent ohmic losses dependent on geometry and material of the wire) appeared to be a phenomenon mainly responsible for transmission degradation. Skin effect significantly reduces possibilities of wide-band digital data transmission along telephone lines. It also limits TDR measurement system resolution and accuracy, which is shown in numerous measurement and computer simulation results.

A pulser with inverted microstrip line for time-domain reflectometry

The paper presents a pulse generator dedicated for time domain relectometry system. The idea of the pulser delivering step pulses with picosecond transition time together with its experimental realization are described. Main features of the presented pulser are: the circuit for shaping output pulses consisting of several stages (each of them containing Step Recovery Diode) connected by inverted microstrip line and the controlled delay of the (also generated) oscilloscope trigger pulses. Time-domain measurement illustrate the achieved results.

Srd-based multistage circuit for shaping picosecond pulses

The paper presents an idea together with its experimental realisation of shaping step pulses with picosecond transition time. Shaping circuit is built from several stages, each of them containing Step Recovery Diode (SRD). Time-domain measurement illustrate achieved results. Computer simulation is shown to be useful to predict circuit behaviour.

Bandwidth broadening of the photodetector signal path

The paper addresses bandwidth widening of an analog signal path, composed of a high-speed infrared photodetector, an amplifier and a transmission line connecting the two. To investigate influence of design variables upon bandwidth a simplified model of the signal path is analyzed first. Several design scenarios are considered, including transmission line length adjustment, but also insertion of a simple LC corrector. Trade-offs between bandwidth and pass-band ripple level are revealed numerically, also for a realistic model of an infrared photodetector, wide band gain-block and a flexible strip line connection. It is shown that the simple T-corrector can result in substantial bandwidth increase. Interestingly enough, in most cases tested similar broadening can be provided by appropriate tuning of the connection line length only.

Small-signal lumped-element equivalent model for high operating temperature infrared photodetectors

We present a simple small-signal parameterized equivalent circuit for HgCdTe photodetectors operating at high temperatures in the middle and long wavelength of the infrared spectrum. This circuit is capable of accurate modeling the impedance of these devices upon bandwidth of several GHz and for a wide range of bias voltage and temperatures. We have implemented this model as a parameterized sub-circuit in generic circuit simulator from SPICE family, to study conditions for signal propagation in the photodetector signal path at low level of IR illumination. Analyses based on this model provide a useful insight into photodiode operation.

Efficient MATLAB simulation of the brusselator

The paper presents the results of the simulation of the brusselator performed in the MATLAB environment. The brusselator is a kind of a chemical oscillating system (with periodically changing concentrations of reactants and the possibility of self-organizing), described by the Partial Differential Equation (PDE) system. The brusselator is analyzed by solving a set Ordinary Differential Equation (ODE) obtained by the space discretization of the original PDE. The resulting ODE system is huge (the better accuracy expected, the more dense discretization and the larger ODE set), so its solving is a highly time-consuming task. This paper illustrates solving brusselator equations by means of the generic mathematical software (MATLAB), using both built-in integrating algorithms, as well as the dedicated iterated integration scheme, with the focus on the efficiency of the simulation.

Remarks on parallel computations in MATLAB environment

The paper attempts to summarize author’s investigation of parallel computation capability of MATLAB environment in solving large ordinary differential equations (ODEs). Two MATLAB versions were tested and two parallelization techniques: one used multiple processors-cores, the other – CUDA compatible Graphics Processing Units (GPUs). A set of parameterized test problems was specially designed to expose different capabilities/limitations of the different variants of the parallel computation environment tested. Presented results illustrate clearly the superiority of the newer MATLAB version and, elapsed time advantage of GPU-parallelized computations for large dimensionality problems over the multiple processor-cores (with speed-up factor strongly dependent on the problem structure).