Roman Sotner

Precise Electronically Adjustable Oscillator Suitable for Quadrature Signal Generation Employing Active Elements with Current and Voltage Gain Control

A new oscillator suitable for quadrature and multiphase signal generation is introduced in this contribution. A novel active element, called the controlled gain-buffered current and voltage amplifier (CG-BCVA) with electronic possibilities for current and voltage gain adjustment is implemented together with a controlled gain-current follower differential output buffered amplifier (CG-CFDOBA) for linear adjustment of the oscillation frequency and precise control of the oscillation condition in order to ensure a stable level of generated voltages and sufficient total harmonic distortion. The parameters of the oscillator are directly controllable electronically. Simultaneous changes of two current gains allow linear adjusting of the oscillation frequency, and a controllable voltage gain is intended to control the oscillation condition. A detailed comparison of the proposed circuits with recently developed and discovered solutions employing the same type of electronic control is provided and shows the useful features of the proposed oscillator and utilized methods of electronic control. Behavioral models based on commercially available ICs have been used for experimental purposes. CMOS implementation of active elements was introduced and utilized for additional simulations and studies. Non-ideal analysis, Monte Carlo statistical evaluations of simulated models, and further analyses were performed for the exact determination of the expected results. Laboratory experiments confirmed the workability and estimated behavior of the proposed circuit as well.

Design of Z-copy controlled-gain voltage differencing current conveyor based adjustable functional generator

This paper introduces interesting active element and its application in the field of square and triangular wave generators. Active element, so-called Z-Copy Controlled Gain Voltage Differencing Current Conveyor (ZC-CG-VDCC), has availability of three mutually independently and electronically adjustable parameters (transconductance, intrinsic resistance of the current input terminal and current gain between two terminals) that are very popular for control of applications today. In addition, a proposed device utilizes very useful z-copy (additional auxiliary terminal) features and two terminals providing voltage difference. All mentioned features are beneficial in mixed-mode circuit synthesis and design of adjustable applications (active filters, oscillators, generators, modulators, etc.). Electronically adjustable properties of the device are involved in the design of an adjustable generator. The generator provides voltage- and current-mode square wave outputs that can be also used for differential square wave output when very simply modified. Application of the generator in simple pulse width modulator (PWM) is also introduced. A detailed analysis and Spice simulation results are given and main features of the circuits are compared to electronically controllable solutions of recent development in this field.

An Additional Approach to Model Current Followers and Amplifiers with Electronically Controllable Parameters from Commercially Available ICs

Several behavioral models of current active elements for experimental purposes are introduced in this paper. These models are based on commercially available devices. They are suitable for experimental tests of current- and mixed-mode filters, oscillators, and other circuits (employing current-mode active elements) frequently used in analog signal processing without necessity of onchip fabrication of proper active element. Several methods of electronic control of intrinsic resistance in the proposed behavioral models are discussed. All predictions and theoretical assumptions are supported by simulations and experiments. This contribution helps to find a cheaper and more effective way to preliminary laboratory tests without expensive on-chip fabrication of special active elements.

An Example of Easy Synthesis of Active Filter and Oscillator using Signal Flowgraph Modification and Controllable Current Conveyors

An Example of Easy Synthesis of Active Filter and Oscillator using Signal Flowgraph Modification and Controllable Current Conveyors The paper deals with synthesis of active frequency filters and oscillators for applications in the video band. The synthesis is based on the modified signal flow graph design approach in the current mode. The commercially available high frequency current conveyors and second order structures are used. Basic structure is employing loss-less and lossy current mode integrators in two distributed feedback loops. Some of the used active elements allow to control current gain which is very useful in applications. High frequency multi-functional filter and electronically adjustable quadrature oscillator configurations are discussed. Most of the used passive elements (mainly capacitors) are grounded which is suitable for IC implementation. Simulation and experimental results demonstrate function and features very well.

New Double Current Controlled CFA (DCC–CFA) Based Voltage–Mode Oscillator with Independent Electronic Control of Oscillation Condition and Frequency

In this paper, a new electronically tunable quadrature oscillator (ETQO) based on two modified versions of current feedback amplifiers (CFAs), the so called double current controlled CFA (DCC-CFAs) is presented. The frequency of oscillation (FO) of the proposed voltage-mode (VM) ETQO is electronically adjustable by current gain or by varying the intrinsic resistance of the X terminal of the active element used. The condition of oscillation (CO) is adjustable by current gain independently with respect to frequency of oscillation. Simultaneous control of current gain and intrinsic resistance allows linear control of FO and provides extension of frequency tuning range. In the proposed circuit all the capacitors are grounded. The use of only grounded capacitors makes the proposed circuit ideal for integrated circuit implementation. The presented active element realized by using BiCMOS technology and the behavior of proposed circuit are discussed in details. The theoretical results are verified by SPICE simulations based on CMOS ON-Semi C5 0.5 μm and bipolar ultra high frequency transistor arrays Intersil HFA 3096 process parameters.

UNIVERSAL TUNABLE CURRENT-MODE BIQUAD EMPLOYING DISTRIBUTED FEEDBACK STRUCTURE WITH MO-CCCII

Universal Tunable Current-Mode Biquad Employing Distributed Feedback Structure with MO-CCCII One possible application of the multiple-output electronically-tunable active building block as a universal filter with distributed feedback structure is presented. The suggested structure is less conventional than the well-known state-variable Kerwin-Huelsman-Newcomb but allows the same filter configurations with the similar properties. The major current-mode design approach disadvantage, ie, the necessity of multiple current outputs, is demonstrated. To date even a rather big line of the commercially available devices do not solve this problem. Some features of the active block used for modelling and transistor-level simulation are briefly discussed. The obvious chance for electronic tuning of the proposed filter is verified.

Modified Current Differencing Unit and its Application for Electronically Reconfigurable Simple First-order Transfer Function

Modified current differencing unit (MCDU) and its simple filtering application are introduced in this paper. Modification of the well-known current differencing unit consists in weight ...

Electronically controlled oscillator with linear frequency adjusting for four-phase or differential quadrature output signal generation

This paper introduces novel four-phase oscillator employing two Dual-Output Controlled Gain Current Follower Buffered Amplifiers DO-CG-CFBAs, single Current Amplifier, three resistors, and two grounded capacitors suitable for differential quadrature signal production floating outputs. To control the frequency of oscillation FO and condition of oscillation CO, only the current gain adjustment of active elements is used. The circuit was designed by well-known state variable approach. The oscillator employs three active elements for linear control of FO and to adjust CO and provides low-impedance voltage outputs. Furthermore, two straightforward ways of automatic amplitude gain control were used and compared. Active elements with very good performance are implemented to fulfill required features. Suitable CMOS implementation of introduced DO-CG-CFBA was shown. Important characteristics of the designed oscillator were verified experimentally and by PSpice simulations to confirm theoretical and expected presumptions. Copyright

Electronically adjustable modification of CFA: Double current controlled CFA (DCC-CFA)

A controllable modification of current feedback amplifier is presented in this contribution. In spite of classical conception, there are two current outputs of both polarities available and two buffered voltage outputs. The control of parameters consists of adjustable current gain between X and Z ports and intrinsic input resistance of current input (X). We proposed complex model of active element, which is based on CMOS and bipolar available transistor models of process technology. Spice simulations confirmed our presumptions and provided features of designed active element.

Reconfigurable Fractional-Order Filter with Electronically Controllable Slope of Attenuation, Pole Frequency and Type of Approximation

This paper presents design of electronically reconfigurable fractional-order filter that is able to be configured to operate as fractional-order low-pass filter (FLPF) or fractional-order high-pass filter (FHPF). Its slope of attenuation between pass band and stop band, i.e., order of the filter, is electronically adjustable in the range between 1 and 2. Also, pole frequency can be electronically controlled independently with respect to other tuned parameters. Moreover, particular type of approximation can be also controlled electronically. This feature set is available both for FLPF and FHPF-type of response. Presented structure of the filter is based on well-known follow-the-leader feedback (FLF) topology adjusted in our case for utilization with just simple active elements operational transconductance amplifiers (OTAs) and adjustable current amplifiers (ACAs), both providing possibility to control its key parameter electronically. This paper explains how reconfigurable third-order FLF topology is used in order to approximate both FLPF and FHPF in concerned frequency band of interest. Design is supported by PSpice simulations for three particular values of order of the filter (1.25, 1.5, 1.75), for several values of pole frequency and for two particular types of approximation forming the shape of both the magnitude and phase response. Moreover, theoretical presumptions are successfully confirmed by laboratory measurements with prepared prototype based on behavioral modeling.