A CMOS monolithic amplifier for cardiac EIT applications

Analog Integrated Circuits and Signal Processing - This paper presents a low-noise amplifier (LNA) with superior linearity for ultra-wideband (UWB) purposes. Linearity is a significant parameter...     

A perfused tissue phantom for ultrasound hyperthermia

A perfused tissue phantom, developed as a tool for analyzing the performance of ultrasound hyperthermia applicators, was investigated. The phantom, consisting of a fixed porcine kidney with thermocouples placed throughout the tissue, was perfused with degassed water by a variable flow rate pump. The phantom was insonated by an unfocused multielement ultrasound applicator and the temperatures in the phantom were recorded. The results indicate that for testing protocols where tissue phantoms are needed, the fixed kidney preparation offers an opportunity to use a more realistic phantom than has previously been available to assess the heating performance of ultrasound hyperthermia applicators.     

A versatile controller for 3-D machining

A controller that produces sculptured surfaces from a small input without postprocessing is presented. It generates straight lines, circular arcs, and algebraic and trigonometric curves in any plane or combinations of such forms to produce complex lines and surfaces for machining applications. The controller is very versatile and can reduce programming costs by orders of magnitude     

A versatile SPICE model for quantum-well lasers

A SPICE equivalent-circuit model for the design and analysis of quantum-well lasers is described. The model is based on the three-level rate equations which include, in their characterization of charge dynamics, the role of gateway states at the quantum well. The model is versatile in that it permits both small- and large-signal simulations to be performed. Emphasis here is placed on validating the model via a comparison of simulated results with measured data of the small-signal modulation response, obtained over a wide range of optical output powers from two lasers with different lengths of the separate-confinement heterostructure (SCH). Using a set of tightly specified model parameters, all the important trends in the experimental data are reproduced. The consideration of gateway states is found to be important, with regard to predicting the small-signal response, only for the laser with the longer SCH. This highlights the significance of the interplay between the roles of transport through the SCH and capture/release via the gateway states at the quantum well     

Generation of anisotropic-smoothness regularization filters for EIT

In the inverse conductivity problem, as in any ill-posed inverse problem, regularization techniques are necessary in order to stabilize inversion. A common way to implement regularization in electrical impedance tomography is to use Tikhonov regularization. The inverse problem is formulated as a minimization of two terms: the mismatch of the measurements against the model, and the regularization functional. Most commonly, differential operators are used as regularization functionals, leading to smooth solutions. Whenever the imaged region presents discontinuities in the conductivity distribution, such as interorgan boundaries, the smoothness prior is not consistent with the actual situation. In these cases, the reconstruction is enhanced by relaxing the smoothness constraints in the direction normal to the discontinuity. In this paper, we derive a method for generating Gaussian anisotropic regularization filters. The filters are generated on the basis of the prior structural information, allowing a better reconstruction of conductivity profiles matching these priors. When incorporating prior information into a reconstruction algorithm, the risk is of biasing the inverse solutions toward the assumed distributions. Simulations show that, with a careful selection of the regularization parameters, the reconstruction algorithm is still able to detect conductivities patterns that violate the prior information. A generalized singular-value decomposition analysis of the effects of the anisotropic filters on regularization is presented in the last sections of the paper.     

A narrow-band level set method applied to EIT in brain for cryosurgery monitoring

In this paper, we investigate the feasibility of applying a novel level set reconstruction technique to electrical imaging of the human brain. We focus particularly on the potential application of electrical impedance tomography (EIT) to cryosurgery monitoring. In this application, cancerous tissue is treated by a local freezing technique using a small needle-like cryosurgery probe. The interface between frozen and nonfrozen tissue can be expected to have a relatively high contrast in conductivity and we treat the inverse problem of locating and monitoring this interface during the treatment. A level set method is used as a powerful and flexible tool for tracking the propagating interfaces during the monitoring process. For calculating sensitivities and the Jacobian when deforming the interfaces we employ an adjoint formula rather than a direct differentiation technique. In particular, we are using a narrow-band technique for this procedure. This combination of an adjoint technique and a narrow-band technique for calculating Jacobians results in a computationally efficient and extremely fast method for solving the inverse problem. Moreover, due to the reduced number of unknowns in each step of the narrow-band approach compared to a pixel- or voxel-based technique, our reconstruction scheme tends to be much more stable. We demonstrate that our new method also outperforms its pixel-/voxel-based counterparts in terms of image quality in this application.     

A quasi-static analysis for a class of induced-current EIT systems using discrete coils

A discrete coil EIT system is investigated for the general case of an eccentric circular inhomogeneity. The solution methodology of the forward problem of this system is explained. An optimization procedure using this forward problem solution is developed to find optimum currents that maximize the distinguishability. For an eccentric inhomogeneity problem, it is shown that the coil currents can be optimized to focus the current density in a region of interest. Optimum coil currents under limited peak coil currents constraint and limited total power constraint are obtained. Representative examples that demonstrate the performance of the system are presented.     

Miniature microstrip antenna with a partially filled high-permittivity substrate

A new technique to reduce the overall dimension of a microstrip antenna using a partially filled high-permittivity substrate is proposed. The miniaturized microstrip antenna for a repeater system in a mobile communication cellular band (824-894 MHz) is designed with the proposed technique and manufactured with light weight and small size. Comparison between simulations, based on HP HFSS software, and measurements are provided.     

A versatile power converter for high-frequency link systems

A single-phase high-frequency link appears to be an attractive alternative to the DC link commonly used in power conversion systems. The authors propose a power converter suitable for one-step conversion of the single-phase high-frequency link voltage to the three-phase low-frequency voltages typically required for interfacing with system sources and loads. The converter utilizes zero voltage switching principles to minimize switching losses and uses an easy-to-implement technique of pulse density modulation for the control of the amplitude, frequency, and waveshape of the synthesized low-frequency signals. Adaptation of the proposed topology for power conversion to single-phase AC and DC voltage or current outputs is shown to be straightforward. The feasibility of the proposed power circuit and the control technique have been experimentally verified     

A versatile monolithic IC building-block for light-sensing applications

An all-bipolar building-block consisting of a linear light-to-current converter, a voltage comparator, and a voltage reference has been developed. This new general purpose IC combines the advantages of silicon photodiode light sensors with the linear signal processing capability of bipolar integrated transistors. In achieving this marriage, new circuit techniques were developed in order to operate at the very low current levels (<1 nA) and over the wide dynamic range of the light input. Besides their normal sensory function, photodiodes were made to serve as active elements in the circuit, taking part in biasing and acting as active loads in circuits that operate entirely on photocurrents. Use of these techniques boosted overall performance and eliminated the need for a light shield over the active-device portion of the die.     

Methods for Compensating for Variable Electrode Contact in EIT

Electrical impedance tomography (EIT) is an imaging modality that currently shows promise for the detection and characterization of breast cancer. A very significant problem in EIT imaging is the proper modeling of the interface between the body and the electrodes. We have found empirically that it is very difficult, in a clinical setting, to assure that all electrodes make satisfactory contact with the body. In addition, we have observed a capacitive effect at the skin/electrode boundary that is spatially heterogeneous. To compensate for these problems, we have developed a hybrid nonlinear–linear reconstruction algorithm using the complete electrode model in which we first estimate electrode surface impedances, by means of a Levenberg–Marquardt iterative optimization procedure with an analytically computed Jacobian matrix. We, subsequently, use a linearized algorithm to perform a 3-D reconstruction of perturbations in both contact impedances, and in the spatial distributions of conductivity and permittivity. Results show that, with this procedure, artifacts due to electrodes making poor contact can be greatly reduced. If the experimental apparatus physically applies voltages and measures currents, we show that it is preferable to compute the reconstruction with respect to the Dirichlet-to-Neumann map rather than the Neumann-to-Dirichlet map if there is a significant possibility that electrodes will be fully disconnected. Finally, we test our electrode compensation algorithms for a set of clinical data, showing that we can significantly improve the fit of our model to the measurements by allowing the electrode surface impedances to vary.      

A versatile data string-search VLSI

A versatile data string-search VLSI has been fabricated using 1.6-μm CMOS technology. The VLSI consists of an 8 K content addressable memory (CAM) and a 20 K-gate finite-state automation logic (FSAL). A number of unique functions, such as strict/approximate-match string search and fixed/variable-length `don't care' operations, were implemented. A total of 217600 transistors have been integrated on an 8.62×12.76-mm die. The unique functions were efficiency tested by the scan path method. The data comparison rate was 5.12 billion characters/s in text-search application     

A novel versatile modulator circuit

A novel versatile modulator that can operate either as a delta modulator, a sigma-delta modulator, an amplitude modulator or a frequency modulator is presented. The proposed circuit mainly composes of a few components: which are three OTAs, one capacitor and two resistors. Among these components, two OTAs and two resistor construct a Schmitt trigger network whereas the other OTA and a capacitor compose an integrator. The advantage of this circuit is that the clock (carrier) signal employed for modulation is inherent in the circuit. No external clock is needed, only the modulating signal is required for an input. With the compactness of the circuit, it is thus suitable for IC realization. The computer simulation based on CMOS technology demonstrates that the results agree well with the theoretical analysis.     

PDM: A versatile digital transmission system for video

This report discusses a pulse density modulation (PDM) video transmission system. PDM is a one-bit digital coding scheme with advantages of transparency due to an inherently extended signal bandwidth and relatively simple decoding; these make it ideal for a variety of applications. The system outlined is designed to carry a single analogue video channel, together with several sound channels, over a 140 or 280 Mbit/s digital transmission-link. An alternative option to the sound channels will be to carry a 2.048 Mbit/s data channel. Since the analogue video input will be PDM coded, this will enable the system to carry video formats which have a flat base-band frequency response requirement of in excess of 20 MHz (such as HDTV), allowing a large degree of flexibility in use.     

A versatile time-domain Reed-Solomon decoder

A versatile Reed-Solomon (RS) decoder structure based on the time-domain decoding algorithm (transform decoding without transforms) is developed. The algorithm is restructured, and a method is given to decode any RS code generated by any generator polynomial. The main advantage of the decoder structure is its versatility, that is, it can be programmed to decode any Reed-Solomon code defined in Galois field (GF) 2^m with a fixed symbol size m. This decoder can correct errors and erasures for any RS code, including shortened and singly extended codes. It is shown that the decoder has a very simple structure and can be used to design high-speed single-chip VLSI decoders. As an example, a gate-array-based programmable RS decoder is implemented on a single chip. This decoder chip can decode any RS code defined in GF (2⁵) with any code word length and any number of information symbols. The decoder chip is fabricated using low-power 1.5-μ, two-layer-metal, HCMOS technology     

A versatile structure for on-chip extraction of resistance matchingproperties

This paper describes a simple test structure to accurately characterize resistance mismatch. The process engineer would use this structure to monitor process variations with respect to contact resistance, spreading resistance, sheet resistance and encroachment, the circuit designer would use the structure to determine the matching properties of the line and how to optimize a resistor layout for matching given a maximum physical size. By direct measurements on the structure, the user will know how well resistors can be matched, and what factors introduce the dominant components of the mismatch     

A versatile monolithic voltage-to-frequency converter

Voltage-to-frequency (V-F) conversion is achieved with high linearity (0.02 percent) using a precise multivibrator with an 80-dB dynamic range. The IC operates from a single, low-current supply and can accept millivolt signals. A unique thermometer output permits direct conversion of temperature to frequency.     

电阻抗成像压控电流源的参数匹配设计

电压控制电流源的性能对电阻抗成像的效果影响很大,分析了由3个ICL7650S运算放大器构成的电压控制电流源电路,通过设置电路中匹配电阻的数值,使该压控电流源满足电阻抗成像系统的设计要求。仿真结果表明,该电压电流源的频率和幅值可调,在频率为10 k Hz~1 MHz范围内输出波形失真小,在信号频率为50 k Hz时输出阻抗可高达1.3 MΩ,信号频率小于150 k Hz时输出阻抗不小于100 kΩ,满足电阻抗成像系统要求。     

Stripline combline filters on substrates designed on high-permittivity ceramic materials

Stripline bandpass combline filters designed on high-permittivity ceramic materials are analyzed. In order to form coupling between codirectional quarter-wave resonators, they are connected in the regions of their short-circuited ends by a stripline conductor. Features of the characteristics of such filters are revealed and compared with the parameters of other ceramic microwave filters. Experimental characteristics of a stripline filter designed on a ceramics with permittivity ?_r = 38 are presented. The experimental results are in good agreement with results of computer simulation.