Lukas Langhammer

Comparison of Two Solutions of Quadrature Oscillators With Linear Control of Frequency of Oscillation Employing Modern Commercially Available Devices

This paper proposes two circuits of frequency-controlled oscillators, whose structures are based only on simple commercially available active elements with minimum number of terminals, in particular, the differential voltage buffer, controllable voltage amplifier and electronically controllable current conveyor. Two methods for achieving linear control (tuning) of frequency of oscillations (FO) are discussed. The first method employs a simple structure. However, the generated signal level (amplitude) depends on the tuning process. This is a drawback of this method. The second method solves this drawback completely, and the generated signals have constant amplitudes during the tuning of FO. The expected behavior is confirmed by laboratory experiments utilizing commercially available high-speed active elements (current- and voltage-mode multipliers, video difference amplifier). Operational range was tested from frequencies of hundreds of kHz up to frequencies of tens of MHz.

Electronically tunable fractional-order low-pass filter with current followers

Proposal of a fractional (1+α)-order low-pass filter is presented in this paper. The proposed filter operates in the current-mode and it is designed using multi-output current followers (MO-CFs) and adjustable current amplifiers (ACAs). The filter possesses ability to electronically control its order and also the pole frequency. Verification of actual function of the filter is supported by the simulation results. The simulations were performed using Pspice simulator. The simulation results for three different values of its order and also three different values of pole frequency are illustrated and compared in this contribution.

Fractional-order high-pass filter with electronically adjustable parameters

This paper presents possible solution of fractional-order high-pass filter (FHPF) with electronically adjustable order between 1 and 2 and also with electronically adjustable pole frequency. It is based on well-known Follow-the-Leader Feedback (FLF) topology adjusted for utilization with operational transconductance amplifiers (OTAs) and adjustable current amplifiers (ACAs). This 3rd-order topology is used in order to approximate FHPF response in particular frequency band of interest. Design is supported by Pspice simulations for three particular values of the filters order (1.25, 1.5, 1.75) and for several values of pole frequency. Moreover, simulation results with two different approximations are compared.

Synthesis and Analysis of Electronically Adjustable Fractional-Order Low-Pass Filter

A proposal of a fractional (1+α)-order low-pass filter is presented in this paper. The proposed filter operates in the current-mode and it is designed using Multi-Output Current Followers (MO-CFs), Dual-Output Current Follower (DO-CF), Dual-Output Adjustable Current Amplifier (DO-ACA) and Adjustable Current Amplifiers (ACAs) as active elements within the presented topology of the filter. The filter possesses ability to electronically control its order and also the pole frequency by changing the current gain of current amplifiers (ACAs) already present in the structure. Three different values of the order and pole frequency of the proposed low-pass filter were tested as an example. Design of the proposed filter is supported by simulation and experimental results. Simulations of the circuit are carried out in PSPICE simulator with behavioral models of used active elements. The experimental laboratory measurements are performed with the help of available devices forming equivalent circuits. Simulations and experimental results of the electronical control of the order and pole frequency are compared in this contribution.

Special electronically reconfigurable lossy/lossless integrator in application of functional generator

This paper deals with idea of an electronically reconfigurable integrator utilized in nonlinear application of functional generator and study of its features in this circuit. The integrator can be electronically readjusted to lossy and lossless type as well as this integrator also offers electronic tuning of time constant. Possibility of simple electronic reconfiguration provides generation of square wave and selection to generate triangular or exponential (relaxation) output waveforms in node of working capacitor. Intentions of synthesis and design were confirmed by PSpice simulations.

Fractional-order low-pass filter with electronically adjustable parameters

This paper presents possible solution of fractional-order low-pass filter (FLPF) with electronically adjustable order between 1 and 2 and with also electronically adjustable pole frequency. It is based on well-known follow-the-leader feedback (FLF) topology adjusted in our case for utilization with operational transconductance amplifiers (OTAs) and adjustable current amplifiers (ACAs). This 3rd-order topology is used in order to approximate FLPF response in particular frequency band of interest. Design is supported by Pspice simulations for three particular values of order of the filter (1.3, 1.5, 1.7) and for several values of pole frequency.

Digitally Controllable Current Amplifier and Current Conveyors in Practical Application of Controllable Frequency Filter

Abstract This paper presents the simulations results in comparison with the measured results of the practical realization of the multifunctional second order frequency filter with a Digitally Adjustable Current Amplifier (DACA) and two Dual-Output Controllable Current Conveyors (CCCII +/−). This filter is designed for use in current mode. The filter was designed of the single input multiple outputs (SIMO) type, therefore it has only one input and three outputs with individual filtering functions. DACA element used in a newly proposed circuit is present in form of an integrated chip and the current conveyors are implemented using the Universal Current Conveyor (UCC) chip with designation UCC-N1B. Proposed frequency filter enables independent control of the pole frequency using parameters of two current conveyors and also independent control of the quality factor by change of a current gain of DACA.

Resistor-less Single-purpose or Reconfigurable Biquads Utilizing Single Z-Copy Controlled-Gain Voltage Differencing Current Conveyor

Presented work deals with applications of the single z-copy controlled-gain voltage differencing current conveyor (ZC-CG-VDCC) in single purpose and multifunctional biquadratic voltage- and current-mode active resistor-less filters. Electronically adjustable features of the active device (intrinsic current input resistance Rx, current gain B and transconductance gm) are controlled by DC bias current. These mentioned adjustable features allow interesting possibilities of control of the pole frequency and quality factor. Four voltage-mode solutions realizing low-pass, band-pass, high-pass and band-reject filtering solutions were designed together with two current-mode filters. The current-mode solutions have curious multifunctional capability based on full utilization of electronically controllable parameters of the ZC-CG-VDCC. Two adjustable parameters of the ZC-CG-VDCC (intrinsic current input resistance and transconductance) are used for electronic setting of features of the filter (pole frequency, quality factor, tuning). Control of the third adjustable parameter (current gain) causes reconnection-less change of the transfer function between iAP (inverting all-pass response) and iBR (inverting band-reject responses). Simulation results in PSPICE and Cadence CDS 6 are used to show characteristics of the proposed circuits.

Fractional-order low-pass filter with electronic tunability of its order and pole frequency

Abstract This paper presents novel solution of a fractional-order low-pass filter (FLPF). The proposed filter operates in the current mode and it is designed using third-order inverse follow-the-leader feedback topology and operational transconductance amplifiers (OTAs), adjustable current amplifiers (ACAs), auxiliary multiple-output current follower (MO-CF) as simple active elements. The filter offers the beneficial ability of the electronic control of its order and also the pole frequency thanks to electronically controlled internal parameters of OTAs and ACAs. As an example, five particular values of fractional order of the FLPF were chosen and parameters of the filter were calculated. Similarly, also electronic control of the pole frequency of the filter was studied. The design correctness and proper function of the filter are supported by simulations with CMOS models and also by experimental laboratory measurements. Comparison of the simulation results of the proposed filter for two different approximations of the parameter sα is also included.

Higher order differentiator block for synthesis of controllable frequency dependent elements

This paper presents structure of generally nth-order differentiator transfer block serving for purpose of integer order or fractional order immittance (impedance) synthesis. Presented structure of the differentiator is based on electronically controllable current conveyors (ECCIIs), current conveyor of second generation (CCII) and electronically controllable gain amplifier (VGA). This structure was applied as example of 3rd order differentiator and frequency dependent negative resistors (FDNRs) of integer (as well as fractional) order. Proposed applications offer electronic controllability of time constant, magnitude value and reconfigurability of impedance character (between positive and negative). PSpice simulations were performed in order to verify presented concepts.