AbstractWhenever a number of signals of differing frequencies pass through a nonlinear device, energy is transferred to frequencies that are sums and differences of the original frequencies, that is, intermodulation products. This article presents a simple intermodulation theory and discusses its limitations and extensions. Methods of characterizing and measuring the intermodulation performance of nonlinear devices are presented, and their merits and demerits are discussed.

This paper presents new electronically tunable bandpass filters. The electronic tuning of the center frequency of each filter can be achieved by adjusting the gain of one or more of the voltage-amplifiers connected in the feedback path of the proposed topology without disturbing the constituents of the filter itself; this results in a shadow filter. Experimental results obtained using the AD741 operational amplifier and the AD844 current-feedback operational amplifier are included.

This paper presents the experimental results obtained from the synchronization of two memristor-based Wien-bridge oscillators. The experimental results show that synchronization is feasible between two chaotic oscillators. This is very important for implementing chaotic-based secure communication systems. The experiment can be easily introduced in an undergraduate laboratory course to demonstrate the feasibility of synchronizing chaotic memristor-based oscillators.

This paper presents a new electronically tunable standard notch, low pass notch and high pass notch filters. All the filters can be obtained from the same topology by adjusting a grounded resistance. The electronic tuning of the notch frequency, the zero frequency and the pole frequency can be achieved by adjusting the gain of a voltage-amplifier connected in the feedback path of the proposed topology without disturbing the constituents of the filter itself; that is a shadow filter Experimental results obtained using the AD844 current-feedback operational amplifier are included.

This paper presents a new current-feedback operational-amplifier (CFOA) based first-order voltage mode all-pass filter (APF). The proposed circuit can be used as a tunable time-delay circuit with relatively large time delays. The circuit enjoys low output impedance and, therefore, can be easily cascaded with similar circuits to obtain larger time delays. The functionality of the circuit was confirmed using PSPICE simulation tool and commercially available integrated circuit (AD844). The simulation results show that delay can be tuned from 10 mu s to 256 mu s.

This paper presents new approximations for the rational-powered membership function generator. These approximations require only a squaring function, a scalar function and a constant. Thus, the realization of the rational-powered function in current-mode is simple, straightforward and uses less number of MOSFETs. Simulation results obtained show that the rational-powered function can be obtained with root mean square (RMS) error less than 0.03 over the normalized input range 0-1 and for a wide range of rational powers. Much less RMS errors can be obtained if the normalized input values are restricted.

A novel electronically tunable shadow comb filter with N notches is presented. The proposed filter is built around the commercially available current-feedback operational-amplifier (CFOA). The bandwidth of each notch can be independently controlled, without disturbing the gain of the comb filter and the notch frequency, by adjusting the gain of an external voltage amplifier built around a CFOA. The gain of this CFOA-based voltage amplifier is controlled by adjusting a variable grounded resistance. This grounded resistance can be implemented, if desired, using an operational transconductance amplifier (OTA) configured as a grounded resistance. The proposed shadow comb filter enjoys the attractive feature of low output impedance. This would facilitate cascading of comb filters to obtain any number of notch frequencies. Experimental results obtained from a shadow comb filter with 4 notch frequencies using the AD844 CFOA are presented. These results confirm the functionality of the proposed comb filter both for low as well as high notch frequencies.

This study introduces the concept of space preferences to enhance the operation of recurrent-users car parking systems. On campus, at KFUPM, several parking buildings are available for students, employees, and faculty. Still, substantial amount of time is wasted just looking for a suitable parking space. The authors propose to enrol all users together with their top ranked preferred parking spots and pedestrian exit of choice. Upon presentation of the user ID card, the system retrieves their preferences, matches them to the updated database of vacant spots, then directs the user to their topmost vacant parking spot. The system directs the user to the nearest parking building if no vacancy. Two options have been evaluated to detect parking vacancies: one is based on ultrasonic sensors and the second uses a set of cameras. The sensor-based system was built around an Arduino platform paired with a wireless channel for communication. For the camera-based system, the authors introduce a new set of features mixing both edge and texture information from the parking spot images. A performance analysis of both systems was carried showing that the sensor-based implementation outperforms the camera-based one for the authors' specific application with an accuracy of 100 and 98%, respectively.

This paper presents new approximations for the rational-powered membership function generator. These approximations require only a squaring function, a scalar function and a constant. Thus, the realization of the rational-powered function in current-mode is simple, straightforward and uses less number of MOSFETs. Simulation results obtained show that the rational-powered function can be obtained with root mean square (RMS) error less than 0.03 over the normalized input range 0-1 and for a wide range of rational powers. Much less RMS errors can be obtained if the normalized input values are restricted.

A new current-feedback operational-amplifier (CFOA)-based floating active inductor (FAI) and capacitance/resistance multipliers is presented. The FAI and the capacitance/resistance multipliers can be used to construct active filters with center/cutoff frequencies in the low frequency range. Experimental results obtained from a bandpass filter constructed using AD844 CFOA confirm the functionality of the proposed circuit. The proposed circuit would be useful for biomedical and seismic applications with center/cutoff frequencies around few Hz.

This paper presents a simple mathematical model for the transfer characteristic of any nonlinear power amplifier. The model yields closed-form expressions for the amplitudes of the fundamental and distortion components of the output resulting from a multisinusoidal input. Using this model an apparatus is proposed to quantify the nonlinear performance of the power amplifier without recourse to the use of expensive electronic measuring instruments and/or sophisticated software. Moreover, the apparatus can provide means for automatic adjustment of the nonlinear characteristics of the pre-distortion network that may be used to linearize the power amplifier. The proposed apparatus is simple and can be built around a microprocessor that can perform addition, subtraction, multiplication and division in addition to storing and moving data from one location to another.

This paper presents a simple chaotic-masking system. The system uses a chaos generator built around a grounded memristor. The memristor is emulated using the current-feedback operational amplifier (CFOA). At the sending end the signal is masked by adding chaos. At the receiving end the signal is recovered by subtracting the chaos. The performance of proposed system is investigated using sinusoidal and square wave signals.

This article shows that an operational amplifier based square/triangular/sinusoidal oscillator circuit can be easily modified to be a chaotic/square/triangular/sinusoidal oscillator by adding two anti-parallel connected diodes. Experimental results that confirm the operation of the proposed modification are included.

This short communication presents further evidence to confirm the caution against using equations obtained by applying the Barkhausen criterion to classify sinusoidal oscillators as enjoying the attractive feature of fully uncoupled frequency and condition of oscillation. In this regard we use the most recently published experimental results.

This paper presents a simple electronic circuit which provides negative group delay (NGD). The proposed circuit is built around the current-feedback operational-amplifier and uses grounded resistors and capacitors. The proposed circuit has a high input impedance and a low output impedance. Thus, obtaining relatively long NGDs is feasible by cascading several circuits. Experimental and simulation results that confirm the functionality of the proposed circuit are included.

This brief presents a new tunable impedance multiplier with high multiplication factor. The proposed design uses a single externally connected resistor and can be made free of passive elements. The proposed circuit can realize a positive or a negative impedance multiplier. The functionality of the proposed design is confirmed using PSPICE simulation and practical measurements. Applications of the design in filters are also presented. The simulation and experimental results show that the new design enjoys a multiplication factor above 400 and 2 Hz to 7 MHz.

In this paper closed-form approximate expressions for the harmonic and intermodulation performance of a radio-frequency plasma capacitor are presented. These expressions are obtained by approximating the nonlinear capacitor-voltage characteristic using a Fourier-series. These expressions are valid over a wide range of the voltage applied across the capacitor and can be used for investigating the large signal performance of the capacitor.

This paper shows that a Wien-bridge oscillator is not always a sinusoidal oscillator.Depending on the differential input voltage of the operational amplifier used, the output of the Wien-bridge oscillator can move from a nearly sinusoidal wave to a nearly square wave. This depends largely on the values of the passive components used. Experimental results that confirms the presented theory are included. These results confirm the previously made observations that sinusoidal oscillators and multivibrators are not separate classes of circuits as the same circuit can provide the two modes of operation depending on the values of the passive components used.

This paper presents closed-form expressions for the amplitudes of the harmonics and intermodulation products resulting from driving a Mach-Zehnder optomodulator by a multisinusoidal RF voltage. These expressions are functions of the phase shift caused by the DC bias, phi(BIAS), and the modulator's switching voltage, V-pi, required to change the output light intensity from its maximum value to its minimum value. The special case of a driving two-tone equal-amplitude RF voltage is considered in detail. The results show that the harmonic and intermodulation performance of the Mach-Zehnder optomodulator are strongly dependent on the parameters phi(BIAS) and Vp. These parameters are strongly dependent on many physical and chemical phenomena; for example irradiation intensity and temperature variations. Using the results obtained in this paper, a data base can be established for the variation of the harmonic and intermodulation performance of Mach-Zehnder optomodulators with many physical and chemical phenomena. This would be of interest for any potential space application using Mach-Zehnder optomodulators where temperature and/or irradiation effects are of special concern. Simulation results obtained using the harmonic balance simulator controller in the Advanced Design System (ADS) design automation software are included.

This paper discusses the accuracy of the conclusions obtained based on using the Barkhausen criterion for finding the frequency and condition of oscillation of the Wien-bridge oscillator. Such conclusions may be misleading. This suggests that the text-books, classroom analysis and the engineering practice must be changed to introduce the methodology based on finding the roots of the characteristic equation as an alternative route to find the frequency and the condition of oscillation.