Lukas Langhammer

The paper introduces a systematic approach to the design of reconnection-less reconfigurable filters based on the Method of Unknown Nodal Voltages (MUNV). The used approach of previously proposed filters is based on the trial and error (personal experience) selection of parameters of the factorization of the algebraic complements for Laplace expansion of the sub-determinants while the newly proposed approach consists of the gradual placement of individual parameters into the specific matrix element(s) based on the knowledge of which position in the matrix is reflected in particular terms of the transfer function. The proposed approach provides following advantages in comparison to the standard MUNV: a) a more systematic design of MUNV based reconnection-less reconfigurable filters, b) it only requires returning to the selection of signs of individual parameters when the resulting transfer function does not meet its desired form, c) it can be adjusted for different circuits other than reconnection-less reconfigurable filters. The introduced approach is tested and verified for several previously proposed reconnection-less reconfigurable filters (based on MUNV method) and newly presented solution. The possibility to design other circuit types (shown for the design of an oscillator) is also presented. The behavior of the proposed filter is supported by PSpice simulations and experimental measurements in order to verify the design approach.

This paper compares the analytical approach and optimization algorithm for designing a two-bilinear-section-based two-port transfer function hinged on a numerical sweep with the intention of implementing fractional-order (FO) systems in many sensing areas. The study compares analytical and algorithm-based design approaches and tests their effectiveness in designing a two-port system that accommodates phase shifts within the 10° to 80° range and with various phase ripple limits. The impact of phase changes on usable bandwidth (yield maximization) is also explored. The proposed algorithm represents the most optimal approach and calculates zeros/poles frequencies to precisely keep the required mean phase value and phase ripple value for the defined center frequency. Experimental results are provided, utilizing two bilinear sections featuring the current feedback amplifier. Moreover, the implementation of the novel two-port Cole model as an application example of the proposed design is presented and evaluated. The approaches presented are useful in sensing, modeling, and instrumentation.

This paper presents electronically tunable current conveyors using low-voltage, low-power, multiple-input operational transconductance amplifiers (MI-OTAs). The MI-OTA is realized using the multiple-input bulk-driven Metal Oxide Semiconductor transistor (MIBD-MOST) technique to achieve minimum power consumption. The MI-OTA also features high linearity, a wide input range, and a simple Complementary Metal Oxide Semiconductor (CMOS). Thus, high-performance electronically tunable current conveyors are obtained. With the MI-OTA-based current conveyor, both an electronically tunable differential difference current conveyor (EDDCC) and a second-generation electronically tunable current conveyor (ECCII) are available. Unlike the conventional differential difference current conveyor (DDCC) and second-generation current conveyor (CCII), the current gains of the EDDCC and ECCII can be controlled by adjusting the transconductance ratio of the current conveyors. The proposed EDDCC has been used to realize a voltage-to-current converter and current-mode universal filter to show the advantages of the current gain of the EDDCC. The proposed current conveyors and their applications are designed and simulated in the Cadence environment using 0.18 μm TSMC (Taiwan Semiconductor Manufacturing Company) CMOS technology. The proposed circuit uses ±0.5 V of power supply and consumes 90 μW of power. The simulation results are presented and confirm the functionality of the proposed circuit and the filter application. Furthermore, the experimental measurement of the EDDCC implemented in the form of a breadboard connection using a commercially available LM13700 device is presented.

The design of a low-pass-frequency filter with the electronic change of the approximation characteristics of resulting responses is presented. The filter also offers the reconnection-less reconfiguration of the order (1st-, 2nd-, 3rd- and 4th-order functions are available). Furthermore, the filter offers the electronic control of the cut-off frequency of the output response. The feature of the electronic change in the approximation characteristics is investigated for the Butterworth, Bessel, Elliptic, Chebyshev and Inverse Chebyshev approximations. The design is verified by PSpice simulations and experimental measurements. The results are also supported by the transient domain response (response to the square waveform), comparison of the group delay, sensitivity analysis and implementation feasibility based on given approximation. The benefit of the proposed electronic change in the approximation characteristics feature (in general signal processing or for sensors in particular) is presented and discussed for an exemplary scenario.

The paper introduces a novel design solution of a reconnection-less reconfigurable filter based on the method of unknown nodal voltages (MUNV). The filter offers all standard 2 ^nd -order transfer functions, the electronic adjustment of the pole frequency and quality factor, which are mutually independent. The introduced design bring following advantages in comparison to other relevant solutions (MUNV-based reconnection-less reconfigurable filters): a) it consists of four independent nodes which bring the advantage of both working grounded capacitors as floating capacitors can cause unpredictable parasitic behavior, b) the additional adjustment of the quality factor, c) the additional adjustment of the pass-band at lower and higher frequencies. Simulations and experimental measurements were carried out in order to verify the proposed design.

A novel electronically reconfigurable fractional-order filter allowing independent electronic frequency tuning and switchless change of the transfer response by a single parameter between standard band-pass, inverting all-pass response and special type band-reject response is presented in this work. The differences between these special transfer characteristics and standard features consist in magnitude and phase response behavior. Inverting amplification or attenuation is also available. The filter has tested frequency range between 1 Hz and 100 kHz. The proposed fractional-order filter (using two fractional-order element having equivalent capacity 8.7 uF/sec^1/4, $\alpha =3$ /4) tunability yields one-decade range approximately between 10 Hz and 100 Hz by transconductance between 0.19 and 1.1 mS (fractional-order design helps with reduction of driving force less than one decade). The application example in frequency/phase detector (operationability around center frequency 100 Hz - between 50 and 180 Hz) and further signaling frequency detecting system for frequency shift keying demodulator offers maximal detectable voltage (about 300 mV) for alignment (zero phase shift) of the signals of the same frequency (center frequency of the proposed filter in inverting all-pass mode). It also offers an interesting application in frequency shift keying demodulation process (or for identification/signalization purposes of certain frequencies) by usage of a simple additional comparator generating clear output state. Cadence simulations as well as experimental tests using integrated cells of special multipliers fabricated in ON Semiconductor $0.35~\mu \text{m}$ I3T25 CMOS process confirm operationability of the proposed concept as well as simple application of special response of the filter for phase/frequency detection and demodulation purposes.

A design of a fractional-order (FO) integrator is introduced for the operation of the resulting solution in the current mode (CM). The solution of the integrator is based on the utilization of RC structures, but in comparison to other RC structure based FO designs, the proposed integrator offers the electronic control of the order. Moreover, the control of the proposed integrator does not require multiple specific and accurate values of the control voltages/currents in comparison to the topologies based on the approximation of the FO Laplacian operator. The electronic control of a gain level (gain adjustment) of the proposed integrator is available. The paper offers the results of Cadence IC6 (spectre) simulations and more importantly experimental measurements to support the presented design. The proposed integrator can be used to build various FO circuits as demonstrated by the utilization of the integrator into a structure of a frequency filter in order to provide FO characteristics.

The paper presents a novel solution of a fully-differential 1+α fractional-order filter. The filter can provide low-pass, high-pass, band-pass and band-stop transfer functions without a necessity of a circuitry change (filter is electronically configurable). The proposed filter also provides the electronic control of its parameters such as the fractional-order of the filter, pole frequency as well as quality factor. Operational Transconductance Amplifiers (OTAs), Adjustable Current Amplifiers (ACAs) and Fully-Differential Current Follower (FD-CFs) were used in the proposal. The proposal is supported by PSpice simulations using transistor-level models of used active elements.DOI: http://dx.doi.org/10.5755/j01.eie.24.5.21841

This paper shows the topology design of a simple second-order oscillator based on two three-port current conveyors, two resistors, and two grounded capacitors, as well as its modification to a voltage-controlled oscillator (VCO). In comparison with many previous works, the following useful conceptual novelties and improvements were made in this study. Both resistors presented in the topology can be employed to tune of the oscillation frequency by the simultaneous driving of two optocouplers with resistive output stage. The current gain of the current conveyor ensures the control of the oscillation condition. The proposed solution offers advantages (in comparison with many standard so-called single-resistance-controllable types) of improved dependence of the frequency of oscillation (FO) on a driving force (extended tuning of the FO), constant ratio of amplitudes of generated waveforms when the FO is tuned, low complexity (taking into account auxiliary circuitry for optocouplers), and comfortable tuning of the FO by a single control voltage. The oscillator produces waveforms with tunable frequency having a constant 45-degree phase shift between them. The relative sensitivities of the proposed solution achieve typical values for these second-order systems (−0.5). Experimental verification confirmed the expected behavior in the operational band between 1 and 10 MHz tuned by a DC voltage from 1.7 to 5 V. This indicates a significant reduction of the driving force ratio (3:1 in our case) in comparison with standard tuning approaches required for a ratio of 10:1 for FO adjustment. Output amplitudes reached 100 and 150 mV in the observed tunability range with distortion ranging between 0.7 and 3.3%.