Low-Voltage digitally controlled fully differential current conveyor

Design and simulation of a digitally controlled CMOS fully differential current conveyor (DCFDCC) is presented. A novel current division network (CDN) is used to provide the digital control of the current gain between terminals X and Z of this DCFDCC. The proposed DCFDCC operates under low supply voltage of /spl plusmn/1.5 V. The realization of the DCFDCC using the new CDN is presented by two approaches. First approach has linearly proportional current gain with the digitally controlled parameter of the CDN, while the second approach exhibits current gain between terminals X and Z greater than, or equal to, one. Applications of the DCFDCC in realizing second order universal active filter and variable gain amplifier are given. PSPICE simulation confirms the performance of the proposed blocks and its applications.     

Model Order Estimation for Joint Demodulation in DS-CDMA Systems

An iterative algorithm for estimating the number of relevant transmission paths characterized by the model order vector L in the uplink of a direct sequence code division multiple access (DS-CDMA) system is presented. Estimates of simplelower bounds on the probability of correct one-shot symbol estimates are formulated as a function of bit-error rate estimates of all users and maximized w.r.t. L. The joint demodulation for a given value Lis accomplished using a combination of a space-alternating generalized expectation-maximization (SAGE) algorithm for channel parameter estimation and a°multistage detector. Simulation results indicate that the modelorder is estimated correctly even in situations with considerably differentsignal power levels.     

Hidden Markov Modeling of Error Patterns and Soft Outputs for Simulation of Wideband CDMA Transmission Systems

In this paper, a Hidden Markov Modeling (HMM) technique for a fast and accurate simulation of bit errors and soft outputs in wireless communication systems is presented. HMMs with continuous probability distributions are considered. Soft outputs and bit errors are combined to error patterns. We focus on binary phase–shift keying (BPSK) modulation for direct–sequence spread spectrum (code–division multiple access, CDMA) transmission as proposed e.g. for the third generation wireless communication system UMTS (uplink for the frequency division duplex mode (FDD)). Comparisons of simulated bit error rates for HMM models and Rake receivers are shown for AWGN, flat fading, and vehicular channel conditions. In order to assess the ability of the HMM to describe the dynamical behaviour of the channel a comparison for transmission with interleaving and convolutional coding is presented. Furthermore calculated autocorrelation functions of the error patterns and error gap distributions corresponding to the Rake receiver and to the HMM, respectively, are presented. Our investigations show a strong dependence of the required HMM order on E_b/N₀ and the channel conditions. The degree of accordance of the HMM outputs and the training data is examined based on calculated statistical scoring indicators.     

Neural Computation of the MoM Matrix Elements for Planar Configurations

In this paper a new artificial neural network (ANN) based model for the calculation of the method of moments (MoM) matrix elements is presented. Training sets that characterize the matrix elements are first constructed. These sets are then utilized to effectively train two radial basis function (RBF) neural networks to accurately estimate all the elements of the MoM matrix for any mesh used. The potential of the proposed approach is demonstrated in the case of a narrow microstrip line. The current distribution on the microstrip line produced by the trained RBF networks agrees very well with the exact distribution. In addition, the proposed ANN model is much faster than the conventional MoM procedure.     

Two digitally programmable gain amplifiers based on current conveyors

Two digitally programmable gain amplifiers based on current conveyors (CCIIs) are presented. The first digitally programmable gain amplifier consists of a CCII, an operational transconductance amplifier (OTA), and current mirrors. The second one is composed of current conveyor analogue switches (CCASs). Both proposed digitally programmable gain amplifiers do not need switches but they maintain the linear gain at any digital signal levels similar to the digitally programmable gain amplifier using switches; hence the proposed amplifiers are easier to realize, use narrower chip area, and consume lower power. The first proposed amplifier is verified by constructing the circuit using the CCII in an AD844 IC, the OTA in a CA3080 IC, and some bipolar current mirrors. The second proposed amplifier is verified by simulating the circuit using the parameters extracted from the layout (including parasitic capacitance) in the 0.25 μm MOS technology, the level 49 MOS model obtained through MOSIS is used. The results show that the operations of two proposed amplifiers are in accordance with the theories.     

Experimental Verification of an On-Line Calibration Algorithm for a Circular CDMA Antenna-Array

We present a new on-line internal calibration algorithm for a CDMA (code division multiple access) antenna array. The proposed calibration algorithm gives an accurate calibration vector, and as byproducts, the vector-channel parameters of an arbitrarily selected reference user.     

Asymptotic Analysis of Optimal Uniform Polar Quantization

In this paper the simple and complete asymptotically analysis is given for a uniform polar quantizer with respect to mean-square error (MSE) i.e.granular distortion (D_g). We also give the conditions for optimality of the polar quantizer and all main equations for phase partitions and optimal number oflevels are presented. We derive the D_g^opt in a closed form. Thegain ofoptimal uniform polar quantization over product polar quantizations [1–3], is afforded by allowing a variable number of phasesat each magnitude level. We also obtain gain (G) in a closed form.     

Novel All-Pass Filter Section Using Differential Difference Amplifier

A novel high-performance first-order all-pass filter employing a single active element and a minimum number of passive components is presented. The proposed circuit is based on differential difference amplifier and is very suitable for low voltage operation. Also, the use of grounded capacitor enables its implementation with standard CMOS technologies. SPICE simulation and experimental results verifying theoretical analyses are also provided.     

Robust Space Time Receiver for CDMA-based Antenna Arrays

In this paper, we propose a new robust code division multiple access (CDMA) receiver of which weight vector is obtained by projecting the effective spatio-temporal signature waveform onto the signal subspace of the data covariance matrix. We verified our proposed algorithm by the field measured data obtained with a custom-built wideband CDMA test-bed. It will be shown that the proposed algorithm is robust to the signal mismatch.     

Low-Voltage Low-Power CMOS RF Four-Quadrant Multiplier

This paper describes a CMOS four-quadrant multiplier intended for use in the front-end receiver by utilizing the square-law characteristic of the MOS transistor in the saturation region. The circuit was simulated in standard 0.5 μm CMOS level 3 MOSIS (BSIM3 SPICE-based). The mixer has a third-order inter modulation (IM3) of 34.7 dBmV, a third-order intercept point (IP3) of -5.7 dBm, 1-dB compression (P-1dB) of -10.4 dBm and the power consumption is 1.18 mW from a single 1.5 V power supply. One of the features of the proposed design is using two MOS transistors limitation to reduce the supply voltage, which leads to reduce the power consumption.     

Time Offsets for Non-orthogonal CDMA Signals

A simple interference reduction method for non-orthogonal downlink CDMA channels is presented in which non-orthogonal CDMA signals are transmitted with different time offsets. An expression of multiple access interference (MAI) is developed and a reduction of MAI power is evaluated by using a numerical method and a computer simulation. The value of the time offset is determined in order to minimize the MAI and the implementation complexity. The performance of the proposed method is evaluated for various channel models.     

Digitally programmable high-order current-mode universal filters

New high-order current-mode (CM) filter topologies capable of providing all functions simultaneously are presented. The proposed filters are based on digitally controlled current amplifiers and unity gain voltage buffers. The gains of the current amplifiers are digitally programmed to adjust the filters’ transfer function coefficients. It is shown that the proposed approach results in more efficient realizations compared with its counterparts based on other CM active elements. Using BSIM3 0.18 μm CMOS models, simulation results of a fourth-order universal filter are provided.     

Near Field Analysis of the Modal Scattering at Radiating Apertures

A rigorous method for the determination of the modal scattering at radiating apertures is presented. Near-field boundary conditions to be satisfied on the outer surface of the conducting structure containing the aperture (e.g. a horn antenna) are completely taken into account. The resulting scattering matrix of the radiating aperture can be integrated into any mode-matching technique as a termination for the cascaded structure commonly used to match the aperture to the exciting waveguide. The method is based on a multiple-multipole expansion of the electromagnetic field outside the radiating object in conjunction with a point-matching technique. Horn antennas with elliptical and circular apertures have been analyzed using the suggested method. Excellent agreement with measurement results has been achieved for both the radiation pattern and the aperture scattering parameters.     

Selection of Input Stimulus for Fault Diagnosis of Analog Circuits Using ARMA Model

The paper addresses the problem of fault diagnosis of analog circuits based on dictionary approach. The proposed approach first identifies an adequate set of test frequencies to optimize the process of detection and isolation of simulated fault scenarios. The circuit under test (CUT) is then excited by an input stimulus composed of a set of sinusoidal waveforms with the selected test frequencies. The circuit response, at different fault scenarios, is preprocessed by an autoregressive moving average (ARMA) model to yield a set of features formulating the fault dictionary. Collected features are utilized to train and test a back-propagation (BP) neural network (NN) based classifier. Demonstrative results from soft fault simulation of two active circuit examples prove the excellent effectiveness of the proposed algorithm.     

Plasmatron with Microwave Excitation of Nonequilibrium Plasma

Testing results of a microwave plasma generator (plasmatron) intended for excitation of a strongly nonequilibrium plasma arepresented. Nonequilibrium properties of the plasma are described in detail.The plasma flame is formed at an open end of a coaxial line under atmospheric pressure. Argon is used as plasma forming gas, and a 10 GHz CW magnetron with 10 W output power is used for plasma excitation.The efficiency of absorption of microwave power in the plasma is higher than90% with specific absorbing capacity of 0,4.4 kW/cm³     

Space-Time Code Construction Using the Code Factorization Technique

A space-time block code construction is presented which achieves maximum diversity for multi-antenna transmission. The construction is based on selected cyclotomic cosets of an extension field which are multiplied together to give a set of transformation polynomials. A space-time factorization code [1] can be constructed by encoding the information vector by different polynomials to form a set of codeword matrices. Codes are constructed over the Galios field GF(2) and mapped to the BPSK signal constellation. The effect of this mapping on the code design criteria is investigated. Simulation results are compared with the statistical properties of the codes based on the design criteria from [2] and [3].     

Configurations Optimizing the Directivity of Planar Arrays

The role of the geometrical configuration of isotropic elements in a planar array is investigated with a view to achieve maximum directivity. Distinctions are made between normal and superdirective regions. It is further shown that the configurations leading to optimum directivities may depend on aperture diameter in a manner somewhat analogous to phase transitions in solid state physics. The effect of losses is estimated and it is shown that, particularly for superconductive materials, they do not affect much the achievable gain.     

Space-time MSK Codes for Quasi-Static Fading Channels

In this paper, 4-state and 8-state space-time trellis codes with full rate, full diversity and high coding gain are proposed for MSK modulation, based on a technique similar to the super-orthogonal space-time trellis code (SOSTTC) design. Since the phase continuity requirement of MSK is the main constraint in space-time MSK code design not all the signal matrices corresponding to the trellis branches are orthogonal. The paper shows that the SOSTTC design technique can be extended to nonorthogonal coding structures. The new space-time MSK codes have frame error performances very close to those of their space-time QPSK counterparts given in [1]     

Electromagnetic Scattering by an Inhomogeneous Impedance Cylinder

In this paper, the electromagnetic scattering problem related to a circular cylinder with inhomogeneous impedance boundary is solved. This kind of problem may have practical applications such as antenna design since one can obtain a certain radiation pattern by choosing thesurface impedance in an appropriate way. The approach presented in this paper is based on the series representations of the scattering and incident fields. The impedance function is also expanded into a Fourier series. By using orthogonality properties of some special functions the problem is reduced to the solution of a system of linear equations. The problem isalso solved through the extended boundary condition method (T-matrix method). Since an extensive treatment of the T-matrix method is available in the open literature the paper is weighted towards the Fourier series method. The results of both methods are compared. Some illustrative examples showing the effects of different parameters on the scattered field are given.     

Realization of Voltage and Current Mode KHN Biquads Using CCCIIs

In this work, new Kerwin-Huelsman-Newcomb (KHN) biquads employing current-controlled current conveyors (CCCIIs) in voltage-mode (VM) as well as in current-mode (CM) are presented. The parameters of the proposed circuits can be electronically controlled thanks to the tunability properties of the CCCIIs. The VM circuit is derived from a previously reported one by modifying its summing circuit and replacing the current conveyor(CCIIs) and resistors at their x-input terminals with CCCIIs. On the other hand, the CM circuit is derived from the adjoint graph of the signal-flow graph corresponding to the classical KHN circuit. This circuit is a multi-input single-output CM universal filter, which offers all the main advantages of the CM circuits as well as those of the classical KHN circuit. In addition to the three basic filter responses, they also allow the realization of the notch and the all pass responses.