Reliable CAD Analyses of CMOS Radio Frequency and Microwave Circuits Using Smoothed Gate Capacitance Models

The problems with convergence caused by both voltage- and charge-controlled models of MOSFET gate capacitances are often a limiting factor of the computer aided design tools. In the paper, an idea of the exponential smoothing of model discontinuities is proposed. The method is demonstrated on smoothing the gate capacitance discontinuity at zero drain-source voltage. An advanced integration algorithm convenient for the computer aided design of radio frequency and microwave CMOS circuits suppressing possible physically incorrect results of the traditional methods is also described. The updated model and algorithm are checked by analyzing a sophisticated CMOS flip-flop circuit.     

Flexible Digital Receiver Architecture with Optimized Components

Future wireless communication systems require increased flexibility, lower power consumption, smaller size and decreasing costs for the terminals and therewith for the components. By replacing analogue by digital signal processing the degree of integration and the flexibility of a terminal with respect to multi-mode capability can be improved.In a highly integrated implementation the most critical components are the A/D-converter and the digital filter stages due to high speed and low power requirements. In this contribution a novel concept for a flexible, digital receiver with highly optimized components will be presented. The concept is based on down-conversion of the broadband receive signal to a low intermediate frequency. The main modules of the receiver are a properly designed ΔΣ-modulator for A/D-conversion, and novel digital filtering stages. It will be demonstrated, that the use of cascaded low-order wave digital lattice filters results in a number of advantages and makes a very efficient realization in VLSI-technology feasible.     

Analysis of the Collocation Method for Simulating the Propagation of Optical Pulse Sequences

In analogy to the standard Split-Step Fourier algorithm for calculating the signal transmission through optical fibers, a Split-Step collocation algorithm is applied and analyzed in terms of its capability to calculate the propagation of pulse sequences in optical fibers. The method uses a point matching technique for the representation of short optical pulse sequences with Hermite-Gauss functions as basis. This special basis renders time consuming Fast Fourier Transformations (FFT) within the calculation unnecessary. The method is analyzed using realistic NRZ pulse sequences in the simulations. Accuracy and computational effort are evaluated in comparison to the Split-Step Fourier method.     

An Immitance Based Tool for Modelling Passive One-Port Devices by Means of Darlington Equivalents

An immitance-based method is presented to model measured orcomputed data, obtained from a “passive one-port physical device” by means of its Darlington equivalent. In other words, the given data ismodelled as a lossless two port terminated in a unit resistor. The basis of the new modelling tool rests on the numerical decomposition of the given immitance data into its Foster and minimum parts. Therefore, the proposed technique does not require any choice for the circuit topology to build the model. Rather, the optimum circuit topology that characterises thegiven data is the natural consequence of the modelling process proposed in this paper. A main algorithm is presented to construct the model from the given data. It is expected that the proposed modelling tool will findpractical applications in the behaviour characterisation, simulation, and design of high speed/high frequency analog/digital mobile communication sub-systems manufactured on VLSI chips. An antenna-modelling example is included to systematically exhibit the implementation of the modelling technique.     

Low-Voltage Continuous-Time Filter Based on a CMOS Transconductor with Enhanced Linearity

The proposed design of a low-voltage continuous time filter is based on a CMOS transconductor with enhanced linearity. The compensation principle is used for the reduction of transconductor non-linear distortions. The discussed transconductor consists of two transconductors connected in parallel. The input transistors of the first transconductor are working in the triode region, while the input transistors of the further one are in the saturation. A fifth-order 1 MHz low-pass Bessel filter is synthesized and simulated using transconductors. The supply voltage is equal to +2.5 V. A tuning system of the filter is also simulated and discussed. A comparison shows that the discussed filter provides a higher linearity (from 4 to 9 dB) than the known circuits with the exception of filters based on the amplifier with degeneration. But it is noted that the last approach is difficult to use for the low-voltage application, because the voltage drop on the degeneration resistors limits the possible decrease of the voltage supply.     

Modelling of 2-D Real Rational Reactance Functions. A Parameter-Based Approach

Lossless (reactive) one-ports are of great importance in the field of linear network theory. This statement also applies for the two-dimensional (2-D) case, where the design of corresponding impedance or admittance functions is a much more challenging task. In this paper a model for 2-D real rational reactance functions is introduced which is a rational function in p₁ and p₂ where the coefficients are functions of parameters. The following features make it best suited for the computer based design of lossless one-ports, namely no dependencies between the real valued parameters, coverage of the whole class of 2-D real rational reactance functions, and the coefficients are polynomials in the parameters. The synthesis of 2-D lossless networks and skew symmetric matrices form the basis of our considerations.     

A Non-Linear Multiuser Detector for UMTS

The family of international standards for mobile communications IMT-2000 includes amongst others the UMTS Terrestrial Radio Access (UTRA) proposal, which consists of two modes: Frequency Division Duplex (FDD) and Time Division Duplex (TDD). Both are wideband CDMA systems. CDMA systems are Multiple Access Interference (MAI) limited. Conventional detectors like the RAKE receiver do not decrease the MAI, this leads to a limited Bit Error Rate (BER) performance. For further improvement of system capacity Multiuser Detectors (MUD) should be applied. In this paper a non-linear approach employing Radial Basis Functions (RBF) is shown. The adaption of this algorithm to UTRA, its complexity and the BER-performance is discussed.     

Recursive Halfband-Filters

The paper describes the properties and the design of recursive halfband-filters.The two possibilities of being complementary are introduced. The lowpass with the transfer function H_Lp(z)and the corresponding highpass, described by H_Hp(z) = H_Lp(-z)can either be strictly complementary or power complementary. According to the respective symmetry, the impulse responses, transfer functions and frequency responses possess certain characteristic properties, which are described in section 2. It turns out that these resulting symmetries of the frequency response reduce the number of the choosable design parameters. We can only prescribe the cutoff frequency and the tolerated deviation either for the passband or the stopband.

In the third section we treat the design of halfband-filters with approximately linear phase. By coupling an appropriately designed allpass of even degree n_A with a delay of order m=n_A±1 we obtain the desired solution by solving a corresponding approximation problem for the phase of the allpass. The resulting lowpass and highpass are strictly as well as power complementary!The kind of approximation will be done in the sense of maximal flatness, where a closed form solution exists [8], or in the sense of Chebychev, where the solution is obtained iteratively [13]. The design of systems with minimum phase is presented in section 4. The resulting lowpass and highpass are power complementary. Closed form solutions yield Butterworthand Cauer filters, if a maximal flat or a Chebychev approximation is desired. In all cases a fixed relation exists between the passband frequency Ω_P and the tolerated deviation δ_P in the passband when the degree n has been chosen.     

Neural Models for the Resonant Frequency of Electrically Thin and Thick Circular Microstrip Antennas and the Characteristic Parameters of Asymmetric Coplanar Waveguides Backed with a Conductor

Neural models for computing the resonant frequency of electrically thin and thick circular microstrip antennas, based on the multilayered perceptrons and the radial basis function networks, are presented. Five learning algorithms, delta-bar-delta, extended delta-bar-delta, quick-propagation, directed random search and genetic algorithms, are used to train the multilayered perceptrons. The radial basis function network is trained according to its learning strategy. The resonant frequency results of neural models are in very good agreement with the experimental results available in the literature. In this paper, the characteristic impedance and the effective permittivity of the asymmetric coplanar waveguide backed with a conductor are also computed by using only one neural model trained by the backpropagation with momentum and the extended delta-bar-delta algorithms. When the performances of neural models are compared with each other, the best results for test are obtained from the multilayered perceptrons trained by the extended delta-bar-delta algorithm.     

Air Cavity Incorporation to LTCC Spiral Inductor for High Q-factor and SRF

We have devised a new LTCC spiral inductor incorporating an air cavity underneath for high Q-factor and high self-resonant frequency (SRF). The air cavity employed under the spiral reduces the shunt capacitance of the inductor, and results in high Q-factor and SRF of the embedded inductors. The optimized spiral inductor with the embedded air cavity shows a maximum Q of 51 and SRF of 9.1 GHz, while conventional spiral inductor has a maximum Q of 43 and SRF of 8 GHz with effective inductance of 2.7 nH.     

A Method for Determining the Number of Base Stations Connected to a BSC in CDMA Cellular Communication Systems

The number of base stations connected to a BSC (Base Station Controller) should be determined by the capacities of CCP (Call Control Processor) and the other resources of the BSC. We can specify the capacity of the BSC in terms of the rates of call connections, soft handoffs, pagings and location registrations. In this paper, we will calculate the occurrence rates of call connections, soft handoffs, pagings and location registrations in the service area of the BSC when the number of base stations connected to the BSC is known. Based on the formulae for the occurrence rates, a method for determining the number of base stations connected to the BSC will be proposed.     

Characteristic Modes for the Multiple Stacked Aperture Problem with Application to the Finite Array Analysis of Flat Plate Slot Array Antennas.

For the emerging market of Direct-to-User Broadcast Satellite TV (DBS-TV), flat plate slot array antennas are currently being designedand commercialized. Although the antenna configuration resembles a FSS (Frequency Selective Surface) slot array, the electromagnetic analysis ofthe antenna problem requires a new approach. The theory of Characteristic Modes is extended to deal with multiple stacked apertures. Entire domain expansion functions are selected from the Characteristic Mode set and used to reduce the computational effort to analyze finite arrays with an orderof magnitude.     

Analysis of Serial and Hybrid Concatenated Space-Time Codes Applying Iterative Decoding

In this letter, we investigate serial and hybrid concatenated space-time (SC-ST and HC-ST) codes applying iterative decoding topologies. The coding operations are based on the concatenation of convolutional coding, interleaving, and space-time coding along with a multiple-transmitter/multiple-receiver diversity system. Through the analysis of the SC-ST and HC-ST coding systems, improved design specifications can be selected for the component encoders with considerations of the wireless channel characteristics. Based on the iterative decoding process and the optimum parameter selection operations, a considerable improvement in the error rate performance is obtained. For the applied specs, the results indicate that at the frame error rate (FER) 10⁻² level the SC-ST coding system provides a coding gain of approximately 3 dB in comparison to the Tarokh, Seshadri, Calderbank (TSC) space-time (ST) code [1], where the HC-ST coding system provides an additional coding gain of approximately 1 dB beyond the SC-ST code.     

A Novel High CMRR High Input Impedance Differential Voltage-Mode KHN-Biquad Employing DO-DDCCs

In this work, a novel circuit configuration for realizing a differential voltage-mode Kerwin-Huelsman-Newcomb (KHN) biquad filter with high common-mode rejection ratio (CMRR) is presented. The proposed circuit is based on using the dual output differential difference current conveyor (DO-DDCC). The circuit uses three DO-DDCCs, two capacitors and five resistors. All the passive elements are grounded, which is important in integrated circuit implementation point of view. The differential voltage input signal is applied to high input impedance terminals, which is important in the voltage-mode operations. SPICE simulation results are included to verify the theory.     

On the Reduction of the Complexity of Realistic Large Scale Network Simulations

Current computer systems allow a realistic simulation with more than 100,000 HTTP/TCP clients, as shown in this paper. However, the complexity of such simulations is high: the required memory and the simulation duration touches reasonable limits. Reducing the complexity by using a smaller number of clients as compared to reality is evaluated in this study. The reduction is performed with increasing the activity of each client keeping the load approx. constant. Further, it is shown that the average number of active clients remains approx. constant. The reduction has two targets: (i) the optimisation of the considered simulation scenario and (ii) to allow for simulations with larger simulation scenarios.

It is evaluated how the reduction affects the following parameters: average traffic load, coefficient of variation, Hurst parameter, end-to-end delay and loss probability. It is shown that only the loss probability is affected by the reduction. The simulation results show that the required memory can be reduced by a factor of 4–8, depending on the error bound, and the simulation speed increased by up to 33%. The gain allows to simulate an equivalent of 1,200,000 instead of 150,000 clients.     

A Novel Three-State ARQ Scheme for Variable Error-Tate Channels

This paper presents a new type of automatic-repeat-request (ARQ) scheme, Three-State ARQ (TS-ARQ), for error control in data transmission over a noisy channel. The new scheme is based on the Go-Back-N (GBN) protocol and uses three different methods of GBN protocols: basic GBN, n-copy GBN and continuous-GBN. The new ARQ model is applicable for channels having the variable noise level going from low through medium until very high levels. As it is known, such wireless channels are to be found in terrestrial and space (satellite) communications. This model is to be used for the estimation of the noise state in the channel and one of the methods is used, depending of the noise level. When the noise level is low GBN-ARQ is used, in the case of the medium noise level the n-copy GBN is used, and if the noise level is high continuous-GBN will be applied. This paper presents the method of determining the parameters and transfer moments from one state to another. An original mathematical model is given, together with evaluation results. These results are compared with the known methods and the conclusion that the described method provides some better performances is drowned. The implementation of this new procedure is simple as described in the flow chart given in the paper.     

Modelling and Simulation of Direction-Selective and Frequency-Selective Mobile Radio Channels

This paper presents a new approach to the design of simulation models for spatio-temporal mobile radio channels, which are important for the design, optimization, and test of antenna array based mobile communication systems. The proposed spatio-temporally correlated simulation model is completely deterministic and enables the emulation of the desired fading behaviour with comparably little effort. Moreover, it can be configured flexibly to simulate not only different kinds of theoretical channels with given spatial, temporal, and frequency correlation properties, but also real-world fading channels for mobile communication systems with adaptive antennas.     

On EBG Structures for Cellular Phone Applications

Electromagnetic Band Gap (EBG) materials exhibit many interesting features for microwave and millimetre wave applications. Recently, the employment of such materials has been proposed for cellular phone applications in order to limit the back-radiation and to prevent the exposure of the user from the electromagnetic field. In this paper, we first present a new way to synthesize EBG structures suitable for very compact layouts and then we apply the technique to verify the attractive features of EBGs in cellular phone applications. We show that the suppression of the surface waves, due to the high impedance behaviour of the EBG materials, does not avoid back-radiation from a cellular phone. Nevertheless, EBG structures permit to improve both the radiation efficiency and the impedance bandwidth of terminal antennas.