High output impedance current-mode all-pass sections with two grounded passive components

Two new first-order, current-mode all-pass sections, each with high output impedance and requiring only two grounded passive components along with a differential voltage current conveyor, are presented. The new circuits require no matching conditions for the realisation of current transfer functions and are simpler than most of the recently available circuits. The effect of parasitics and non-idealities is also considered. PSPICE simulations using 0.5 mu CMOS parameters confirm the validity and practical utility of the proposed circuits. A typical application in realising a new current-mode quadrature oscillator is given. A four-phase quadrature oscillator with high impedance outputs is also given.     

SAW impedance elements

In the past few years a new class of SAW devices has been under development based on the use of one port SAW resonators as lumped elements with their impedance strongly changing in a frequency range of effective SAW excitation. These `SAW impedance elements' can be connected in ladder type, balanced bridge type, or others types of networks to provide desired filter characteristics. In this paper the admittance characteristics of a single element are analyzed using coupling of mode (COM) model simulations. It is found that resonant type characteristics of a long transducer can be described by very simple formulas. The frequency gap between resonance and anti-resonance, important for filter design, is determined practically by the ΔV/V parameter of the piezoelectric substrate used, while the minimum magnitude of the impedance at the resonant frequency is determined by the SAW attenuation. The internal reflections only shift the resonance to the left edge of the stopband not changing other characteristics. A case of a synchronous resonator comprising a relatively short transducer and two reflectors placed on both sides of it is also analyzed. This type of impedance element has smaller frequency shift between resonance and anti-resonance points     

Study of the variation of the input impedance of induction machines with frequen

The results of a study of the variation of three-phase induction machines' input impedance with frequency are proposed. A range of motors were analysed, both two-pole and four-pole, and the magnitude and phase of the input impedance were obtained over a wide frequency range of 20 Hz-1 MHz. For test results that would be useful in the prediction of the performance of induction machines during typical use, a test procedure was developed to represent closely typical three-phase stator coil connections when the induction machine is driven by a three-phase inverter. In addition, tests were performed with the motor's cases both grounded and not grounded. The results of the study show that all induction machines of the type considered exhibit a multiresonant impedance profile, where the input impedance reaches at least one maximum as the input frequency is increased. Furthermore, the test results show that the grounding of the motor's case has a significant effect on the impedance profile. Methods to exploit the input impedance profile of an induction machine to optimise machine and inverter systems are also discussed.     

High-frequency input impedance characterization of dielectric films for power-ground planes

Broadband impedance characterization of high dielectric constant (high-k) films was performed using a coaxial test fixture configuration. The presented coaxial test fixture and broadband measurement methodology of impedance for high-k films minimizes systematic uncertainties by reducing the interconnection inductance and improving the calibration procedure. In the APC-7 configuration, the technique enables accurate evaluation of impedance at frequencies of 100 MHz to 10 GHz with resolution of 0.01 /spl Omega/. The electrical characteristic of high-k films was found to be consistent with a capacitive load without significant contribution from the circuit inductance that typically dominates the high-frequency response. The experimental data and numerical simulations showed that high-k organic-ceramic composite materials could considerably suppress resonant behavior of the power-ground planes. It was found that high-k organic resins filled with ferroelectric ceramic powders exhibit a high-frequency dielectric loss that increases with increasing volume fraction of the ceramic component. The dielectric dispersion and the corresponding dielectric loss of organic-ceramic hybrid materials can serve as an effective mechanism for suppressing the resonant standing waves in power-ground planes.     

Measurements of the dynamic input impedance of a dc SQUID

The impedance of a circuit coupled magnetically via a mutual inductanceM _i to a dc SQUID of geometric inductanceL is modified by the dynamic input impedance of the SQUID, which can be characterized by the flux-to-current transfer functionJ J/;J is the current circulating in the SQUID loop and is the flux applied to the loop. At the same time, the SQUID is modified by the presence of the input circuit: in the lumped circuit approximation, one expects its inductance to be reduced toL ^r=(1– _e ² )L, where _e is an effective coupling coefficient. Calculations of J using an analog simulator are described and presented in the form of a dynamic inductance and a dynamic resistance versus bias currentI and . Experimental measurements of and were made on a planar, thin-film SQUID tightly coupled to a spiral input coil that was connected in series with a capacitorC _i to form a resonant circuit. Thus,J was determined from the change in the resonant freqency and quality factor of this circuit as a function ofI and . At low bias currents (low Josephson frequencies) the measured values of were in reasonable agreement with values simulated for the reduced SQUID, while at higher bias currents (higher Josephson frequencies) the measured values were in better agreement with values simulated for the unscreened SQUID. Similar conclusions were reached in the comparison of the experimental and simulated values of the flux-to-voltage transfer functionV . The reduction in the screening at the higher Josephson frequencies is believed to result from the parasitic capacitanceC _p between the SQUID and the input coil. In contrast to the behavior of the input inductance, the change in the input resistance R _i could not be explained in terms of the dynamic impedance of the SQUID reflected into the input circuit. Instead, R _i was dominated by capacitive feedback between the output of the SQUID and the input circuit viaC _p . The experimental values of R _i were satisfactorily explained by a simplified model that predicts R _i –M _iV ^r (C _p /C _i ).     

A functional for the input impedance of thin electric vibrator

A functional for the input impedance of electric vibrator is derived for the variation of the distribution of vibrator current. Using the approximation of sinusoidal current distribution, a simple approximate formula for the input impedance of a symmetric electric vibrator is derived. The active and reactive components of impedance are calculated versus the ratio of the length of vibrator arm to wavelength for three values of the vibrator diameter.     

Choice of input fields in stochastic finite elements

The problem of the arbitrary choice of variables for random field modelling in structural mechanics or in soil mechanics is treated. For example, it is relevant to ask the question of whether it is best to choose a stiffness field along a beam element or to choose its reciprocal field, the flexibility field, as the input to the stochastic finite element model. To answer this question the focus should be on the error of the output of the mechanical model rather than on the input field itself when discretizing the field through replacing it by a field defined in terms of a finite number of random variables. Several reported discretization methods define these random variables as integrals of the product of the field and some suitable weight functions. In particular, the weight functions can be Dirac delta functions whereby the random variables become the field values at a finite set of given points. The replacement field is often defined as the linear regression of the original field on the considered vector of the weighted integrals of the field. For example, this holds for discretizations obtained by truncation of the Karhunen–Loéve expansion of the field, but only approximately so for truncations of expansions given in terms of any other complete orthogonal function basis. Solely discretizations based on the linear regression method are considered herein. The solution to the problem of best choice of the vector of weight functions is not universal but depends on the mechanical problem under consideration as well as on the choice of the input field. Obviously it makes a difference whether it is the stiffness field or its reciprocal field that is chosen to be represented by a vector of weighted averages of the field. As a test example a lognormal stiffness field along the axis of a linear-elastic Bernoulli–Euler column is considered. Then the exact one-to-one conversion from the stiffness field to the flexibility field is directly obtained. From the form of two functionals that have similarity to the potential energy functional and the complementary energy functional, respectively, both derived from the differential equation of the column displacement and the relevant boundary conditions, it can be expected that the discretization of the flexibility field is preferable over the discretization of the stiffness field. Direct mechanical considerations support this expectation.     

High order polynomial elements with isoparametric mapping

Finite elements with polynomial interpolation functions of a degree higher than 2 are used comparatively little on large FEM systems, except in shell elements. However, the author has had several years' experience in the use of the so-called ‘isoparametric, reduced Hermitian element’,⁴ Which has behaved excellently in an industrial as well as an educational environment. The reason for the interest in the Hermitian concept is that the overcompatibility of the element reduces the number of unknowns, the solution time and the discontinuities in stresses between elements. Explicit formulae for the family of interpolation polynomials of order q and degree p = 2q + 1 are given and hierarchical Hermite elements are introduced. The families of Hermite and serendipity elements are isomorphic and the latter may thus be extended to arbitrary high order. For some problems the equidistant node configuration in Lagrange elements of degree 3 and higher is not optimal with respect to smoothness, and a new type of element, the ‘Lobatto element’, is introduced. The methods consistently produce results of an accuracy which is above the requirements of usual engineering applications, but in graphics smoothness of curves is important for a convincing representation. The methods are of particular interest in industries working with structures composed of almost linear materials with well-known properties.     

Simple model for the input impedance of a wire monopole radiator with a dielectric coat

Closed-form formulae are derived for the input impedance of a wire monopole radiator coated with dielectric and fed through a metal plate. Contrary to the previous models, they can be written in the equation block of a radio frequency circuits simulator. They allow for much faster simulations because they involve little numerical work. The simulation results compare well with the experimental data.     

Utilization of operational amplifiers for raising the input impedance of measuring circuits

Summary The analysis and testing of a matching circuit consisting of two operational dc amplifiers have shown that it is possible by means of this circuit to match dc voltage circuits with a large internal resistance (up to 10 meg) to circuits with a small internal resistance (up to 10 kohm).     

阻抗匹配电路在电子测量仪器前端模拟通道中的应用

阻抗匹配电路是电子测量仪器前端模拟通道中的关键电路.在介绍电子测量仪器前端模拟通道组成、功能的基础七,阐述了阻抗匹配的作用,即实现信号最大功率传输和实现信号无反射传输.分析了选频匹配网络中常用的倒L型网络、T型网络和Ⅱ型网络的电路模型和电路参数设计计算方法,给出了实现阻抗变换的各种电压跟随器的电路结构形式,并对电子测量仪器前端T型阻抗匹配电路参数的计算进行了举例说明.     

Model and measurements of the electrical input impedance of a plate-liquid-plate acoustic resonator

A plate-liquid-plate acoustic resonator is used to measure the acoustic velocity of liquids. An analytical model of the electrical input impedance of the resonator is proposed. Theoretical results are compared with experimental measurements using reference liquids. Accuracy of the sound velocity calculation is found to be better than 1%. Finally, factors limiting the achievable accuracy are discussed