Showing papers in "Frequenz in 2006"

A Modified CMOS Realization of the Operational Transresistance Amplifier (OTRA)

Abstract: A modified CMOS realization of the operational transresistance amplifier (OTRA) is presented. A fair comparison with Salama and Soliman OTRA [1] shows that the modified OTRA provides better performance in all parameters. The OTRA is suitable for analog VLSI applications since it does not suffer from constant gain bandwidth product. Hence, it can exhibit wide bandwidth at high gain values. Moreover, an OTRA based variable gain amplifier (VGA) is introduced. A detailed analysis taking the effect of the finite transresistance gain in consideration is provided. Index Terms – CMOS operational transresistance amplifier, analog VLSI applications, variable gain amplifier, wireless communications,

Quadrature Oscillator Using Current Differencing Buffered Amplifiers (CDBA)

Abstract: This paper proposes a current differencing buffered amplifier (CDBA)-based quadrature oscillator (QO) circuit which has only grounded and virtually grounded capacitors, and good sensitivity properties. Oscillation frequency of this configuration can be made adjustable by using voltage controlled elements (MOSFETs). Its performance is analysed and results of circuit simulations that verify theoretical predictions are presented. Index Terms – Quadrature oscillator, CDBA, all-pass filter

Low-Component-Count Insensitive Current-Mode and Voltage-Mode PID, PI and PD Controllers

Abstract: In this paper, new circuits for realizing current-mode and voltage-mode proportional plus integral plus derivative (PID) controllers, proportional plus integral (PI) and proportional plus derivative (PD) controllers employing only plus-type second-generation current conveyors (CCII+s) as active elements are presented. All of the proposed PID, PI and PD controllers have unmatched passive elements, all of which are grounded. The proposed controllers employ reduced number of active and passive components with respect to traditional opamp based PID, PI and PD controllers. In particular, the proposed current-mode and voltage-mode PD and PI controllers employ minimum number of active and passive components. A closed-loop control system employing the proposed current-mode PID controller is designed and simulated using SPICE. Index Terms – PID controller, PI controller, PD controller, Current conveyor

Electronically tunable current-mode OTA-C biquad using two-integrator loop structure

Abstract: This paper introduces a current-mode biquad using five operational transconductance amplifiers (OTAs) and two grounded capacitors. The basic circuit configuration is obtained from a second-order integrator loop structure with loss-less and lossy integrators. The biquad circuit can realize low-pass, band-pass, high-pass, band-stop and all-pass transfer functions by suitably choosing the current output branches. And the circuit parameters can also be tuned orthogonally through adjusting the bias currents of OTAs. It is made clear from sensitivity analysis that the biquad enjoys very low sensitivity with respect to the circuit active and passive elements. An example is given together with simulated results by PSPICE. Index Terms – Continuous-time filter circuit, Biquadratic circuit transfer functions, Operational transconductance amplifiers, Grounded capacitors

Catalogue of Variable Frequency and Single-Resistance-Controlled Oscillators Employing A Single Differential Difference Complementary Current Conveyor

Abstract: A set of fourteen current-mode sinusoidal oscillators employing a single differential difference complementary current conveyor (DDCCC) is proposed. This is the largest catalogue of sinusoidal oscillators with single resistor frequency control, that use only a single active building block (ABB) and minimum number of passive components. The proposed topologies were automatically designed by a genetic algorithm rather than by a human designer. Some of the synthesized networks have very attractive topological features. PSPICE simulation results and non-ideal analysis of the oscillators has been included. Index Terms – sinusoidal oscillators, current conveyors, genetic algorithms

Signal processing structure for automotive radar

Abstract: Automotive radar sensors will be used in many future applications to increase comfort and safety. Compared to classical radar applications like air surveillance, the automotive radar observation area is rather small, but will contain numerous different targets. Due to the close distance of these objects the target resolution procedures become very important. This paper gives an overview about automotive radar signal processing schemes in multiple target situations. Index Terms – Automotive radar, data association, signal processing, multi target environment

Universal current-mode active-C filters employing only plus-type current controlled conveyors

Abstract: In this paper, two new universal current-mode cascadable active-C filters simultaneously realizing low-pass, band-pass and high-pass responses are proposed. One of the filters can also realize notch and allpass responses with interconnection of the relevant output currents. The presented filters employ only four plus-type second-generation current controlled conveyors (CCCII+s) as active elements and only two capacitors as passive elements. The proposed active-C filters can be tuned electronically, and have low active and passive element sensitivities. Index Terms – Current controlled conveyor, current-mode filter, cascadable

Adaptive Antenna Techniques Applied to Multicast Services in Wireless Networks

Abstract: This paper evaluates and compares different adaptive antenna techniques applied in the context of multicast services. Traditional unicast algorithms, such as the matched filter, zero-forcing, TomlinsonHarashima precoding, and switched fixed beams are formulated for the multicast case. Algorithms which try to improve the performance of the worst user within the multicast group are also analyzed and a new algorithm called USMF is proposed. It is seen that the techniques which treat all the users alike do not perform well when compared to those which focus on the worst user. The spatial correlation of the channel is shown to have a significant impact on the results. The presence of line-of-sight is verified to be beneficial to the performance of the proposed algorithm and the switched fixed beams. Other aspects, such as the transmitter/receiver design and the impact of the multicast group size, are investigated as well. Index Terms – Multicast services, transmit processing, adaptive antennas.

Investigations on UHF RFID wave propagation using a Ray Tracing Simulator

Abstract: This paper focuses on the use of RFID technology in the UHF 868 MHz band for identification of consumer items in a distribution center, warehouse or packing station. Wave propagation between RFID transmitters, passive transponder tags and receivers are simulated with ray tracing in order to analyze the functionality of the system in a realistic environment. Index Terms – RFID, ray tracing, wave propagation, simulation, consumer goods, distribution center, packing station, warehouse, tagging, identification

Faster than the FFT: The chirp-z RAG-n Discrete Fast Fourier Transform

Abstract: DFT and FFTs are important but resource intensive building blocks and have found many application in communication systems ranging from fast convolution to coding of OFDM signals. It has recently be shown that the n-Dimensional Reduced Adder Graph (RAG-n) technique is beneficially in many applications such as FIR or IIR filters, where multiplier can be grouped in multiplier blocks. This paper explores how the RAG-n technique can be applied to DFT algorithms. A RAG-n fast discrete Fourier transform will be shown to be of low latency and complexity and posses a VLSI attractive regular data flow when implemented with the Bluestein chirp-z algorithm. VHDL code synthesis results for Xilinx Virtex II FPGAs are provided and demonstrate the superior properties when compared with Xilinx FFT IP cores. Index Terms – Fast Fourier Transform, OFDM, FPGA, n-Dimensional Reduced Adder Graph

Cascadable multiple-input single-output current-mode universal filter based on current differencing buffered amplifiers

Abstract: A multiple-input single-output current-mode universal filter based on current differencing buffered amplifiers (CDBAs) is presented in this paper. The proposed configuration consists of three CDBAs, two virtually grounded resistors, and two grounded capacitors. By properly selecting the input signals, the filter can realize five standard biquadratic functions, i.e. lowpass, bandpass, highpass, bandstop and allpass current responses from the same circuit topology. The circuit has a low-input impedance and high-output impedance, which can enable cascading in current-mode operation without additional buffers. The natural frequency o and the parameter o/Q are independently controllable. No critical matching condition is required for realizing all the filter responses, and all the incremental parameter sensitivities are also low. The performances of the proposed circuit are confirmed by PSPICE simulations. Index Terms – Current differencing buffered amplifier (CDBA), universal filter

A Ray-Optical Approach to Model the Inter-Vehicle Transmission Channel

Abstract: Inter-vehicle communications (IVC) is expected to enable delivery of a large amount of data to vehicles at short ranges using inter-vehicle wireless links. Motivated thereby, a ray tracing approach to model pthe inter-vehicle transmission channel is presented in this paper. The approach consists of three major parts. A microscopic road traffic model is used to generate time series of instantaneous positions and velocities of vehicles on a predefined lane. Realistic traffic situations can therefore be generated in a quasi-continuous manner, which is a pre-requisite for an accurate description of the time variance of the IVC channel. Depending on morphographic data the environment adjacent to the lane is generated stochastically using appropriate models for several typical objects (buildings, parking vehicles, etc.). The result of the traffic and the environment model are realistic time series of entire traffic scenarios, which serve as input data for the wave propagation simulation. For the latter a full 3D ray tracing approach is used allowing for wide-band as well as narrowband analyses of the IVC channel. Characteristic time series of impulse responses (IRs) of the IVC channel can therefore be calculated directly used for system simulations on link level. Index Terms – inter-vehicle communications, channel modeling, ray tracing

New Universal Biquad Using UCCX Devices

Abstract: The purpose of this article is to derive a modification of the circuit shown in [1]. A new device denoted as 0349 UCCX device was proposed in our Department and developed in the AMI Semiconductor Design Center Brno [2]. This device contains realizations of two network elements: an eight-port universal current conveyor UCC (Fig. 1a) and a four-port zero-class current conveyor CCII+/− (Fig. 1b).

Industrial Level Sensing with Radar

Abstract: This paper deals with the use of radar systems for measuring the level of liquids or solid materials in a tank. This is the most used radar application for industrial purposes. The special requirements are highlighted and the basis for S/N calculation is given. The two main radar methods (pulse and FMCW) as well as some realization examples and components are presented. This paper concludes with some remarks on radio approval activities for these ultra-wide band emitters. Index Terms – Radar, Level sensing, Level measurement, Reflectivity, Pulse, FMCW, Antenna, Frequency band.

Commutation in linear and nonlinear systems

Abstract: In this paper we consider the commutability of linear and nonlinear blocks. We show that linearity is not necessary nor sufficient requirement for the commutability since matrix multiplication is not in general commutative although scalar multiplication is commutative. For linear time-invariant systems following the superposition principle we can use the product of two transfer functions, essentially a set of scalar multiplications, and therefore the blocks commute. On the other hand, some blocks are represented by a matrix, for example linear time-variant blocks and blocks describing I/Q imbalance. Such blocks do not in general commute unless the matrices have some special properties. Furthermore, nonlinear systems are not in general commutative. The commutability is not valid unless there is a special reason for that. Typical examples for commutability include (1) the systems are combined through a commutable operation, or (2) one of the systems is the inverse of the other system. Index Terms – commutability, linear systems, nonlinear systems, time-invariant systems, time-variant systems, inverse systems, predistortion, postdistortion, I/Q imbalance

A New Log-Domain Realization of Two-Integrator-Loop Biquad

Abstract: This paper proposes a new log-domain realization of biquadratic filter, which is systematically derived using the two-integrator-loop and state-space synthesis procedure. The filter is constructed with two integrators and current summer circuit. This biquadratic realizes highpass filter, bandpass filter and lowpass filter simultaneously. The proposed filter has a simple structure and can be electronically tuned. PSPICE simulations are given to confirm the theoretical analysis. Index Terms – Two-integrator-loop biquad, log-domain filters, current-mode circuits, state-space synthesis

New Approach for an Approximate Realization of Rank Order Filtering with Low Complexity

Abstract: In radar systems rank order filtering is used in order to distinguish interesting signals from noise, clutter and interferences. For implementation various algorithms based on sorting procedures or histograms are known typically requiring high complexity in computational load and/or data storage. This paper introduces a new approach for an approximate realization of rank order filters with low complexity. Basis idea is subdividing the total range of possible values in intervals suited to the used number representation, establishing a histogram over these intervals with the quantity of values therein, accumulating the quantities, determining the interval with the searched rank, and approximating the searched value by interpolation in this interval. The quality of approximation can be chosen as good as desired. Index Terms – Filters, Nonlinear Filters, Rank Order, Median, Radar, CFAR

Effects of Metallic Objects on Specific Absorption Rate in the Human Head for 915 and 1900 MHz Mobile Phones

Abstract: This paper presents the numerical evaluation of the specific absorption rate (SAR) inside the human head induced by cellular phones at frequencies 915MHz and 1900MHz by including a metallic spectacle frame and metallic tooth caps. Calculations of the absorption are performed by distinguishing the electrical properties of up to 13 tissue types based on anatomically real head and hand models derived from specially for this work recorded MRI scans of 2mm thickness. The numerical calculations are performed using the Finite Difference Time Domain (FDTD) algorithm with mesh sizes of 2mm.The calculated local SAR values are averaged over 1g and 10g tissues as proposed by IEEE standards. It is shown that, the existence of a metallic spectacle frame may cause an increase in SAR values. However, the results demonstrate that, metallic tooth caps have negligible influence on the SAR values. The interpretation of the computational results in terms of international safety guidelines for human health indicates that the specific absorption rate stays within the limits proposed by CENELEC and IEEE standards for the maximum allowed transmitter power levels in the GSM-, DECTand PCS-systems. Index Terms – Electromagnetic radiation, specific absorption rate, mobile phones, safety standards, method of finite differences

Radar Concepts for Autonomous Vehicles

Abstract: Autonomous vehicles have always been an issue since the invention of the car. Powerful sensors and signal processors are the key components of an autonomous vehicle. For far looking obstacle detection RADAR sensing is a very promising approach. This article shows concepts to realise a RADAR system for obstacle detection. Index Terms – RADAR, autonomous vehicle, ACC

Frequency Estimation in Linear Frequency Modulated Radar Systems

Abstract: In the field of object distance sensing, frequency modulated continuous wave (FMCW) radar sensors that transmit a sinusoidal signal with frequency linearly increasing in time are used in several applications. It is well-known that for FMCW radar the distance measurement reduces to the problem of estimating frequencies in the radar output that are proportional to the round trip delay time (RTDT) from the radar setup to objects in the antenna beam. With the discrete Fourier transformation (DFT) in combination with zero-padding and possible spectral interpolation there is an optimal and efficient solution for distinct single targets available that approaches the Cramér-Rao lower bound (CRLB), the theoretical limit in estimation variance. When location estimates of closely spaced objects are required, signal processing becomes more challenging. In this case, model-based frequency estimators that have been the topic of extensive research during the last two decades, pose an alternative to the traditional DFT-approach. Index Terms – FMCW radar, distance measurement, frequency estimation.

An Introduction to Multihop Multi-Antenna Communications

Abstract: Recently there has been significant interest in the use of multihop wireless links for use in mobile communications. In such a system, data is forwarded by one or more relays from the source to the destination, rather than simply via a direct wireless link. This paper focuses on how such techniques can be combined with antenna array processing techniques, where multiple antennas are used at each terminal. We discuss a novel multihop approach called hybrid relaying, which combines amplify and forward relaying with spatial processing. Its performance is compared with other relaying techniques. We also investigate the best approach to exploiting the availability of multiple relays. Our results suggest it is better to use the single best relay to forward to the destination than to try to forward signals via multiple relays. Index Terms – Wireless Relaying, Multihop, Antenna Array Processing, Multiple Input Multiple Output

Efficient Implementation of Real and Complex Linear-Phase FIR and Minimum-Phase IIR Halfband Filters for Sample Rate Alteration

Abstract: Real halfband lowpass and complex halfband bandpass filters, versatile building blocks in a multitude of DSP applications, are revisited with focus on efficient implementation. Linear-phase FIR and minimum-phase IIR halfband filters are recalled predominatly for sample rate alteration, their computational loads are compared, and optimum signal flow graphs are presented. The same comparisons are carried out for the corresponding complex halfband filters (Hilbert-transformers with their passbands centred at the normalised frequencies of Ωc = ±π/2) with and without an additional frequency offset by ∆Ω = ±π/4. As expected, the smaller the transition width between passband and stopband, the higher the relative advantage of the IIR approach in terms of computation. Yet, there exist ranges of specifications where linear-phase FIR halfband filters outperform their minimum-phase IIR counterparts – even without taking into account the linear-phase and stability advantages of FIR filters.