Josef Slezak

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.

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.

Current mode tunable KHN filter based on controlled MO-CFTAs

This paper deals with application of novel active block called multiple-output current follower transconductance amplifier (MO-CFTA) in multiple-loop structure of current mode active filter. The well-known transconductance amplifier (OTA) is modified in such a way that single-input multiple-output active block is obtained. Using this device in the suggested network structure allows us to achieve low pass (LP), high pass (HP), band pass (BP) and band reject (BR) filter. The effects of the parasitic properties of the active devices as well as biquad sensitivities are briefly discussed. The possibility of electronic tuning of the main parameters of the individual filter configuration is verified.

Influence of mirroring of current output responses through grounded passive elements

The paper deals with a necessity of copping the current output responses flowing trough grounded passive elements in the modern active biquad working in the current mode. It is important to use another active block with low input resistance (current follower, current conveyor, etc.) for the impedance matching. This problem is demonstrated in the simple biquadratic structure using two modern functional blocks and two capacitors. Theoretical analysis of the transfer function (Matlab) is compared with the resulting simulations, where macro models of commercially available devices are used.

Tunable oscillator using two CCTA-s and only grounded passive elements

Paper deals with adjustable current mode oscillator based on novel active element called current conveyor transconductance amplifier (CCTA). This active element is build up based on three diamond transistors (OPA 860). Characteristic equation, oscillation condition, oscillation frequency, sensitivities and major influences of used active elements are discussed. Simulation results supports theoretical assumptions.

Realization of arbitrary transfer current characteristic using transconductors CDTA

Active RC circuits with arbitrary transfer characteristics in current mode are presented in this paper. The given circuits are based on the multiple-loop feedback structure, namely on the follow-the-leader feedback structure with output summation. Modeling by signal flow graph technique is used to modify and transform the structure in current mode. Implementations by multi-output current-differencing-input transconductors (CDTA) are given. Verification and illustration are shown. The designed circuits have been simulated in PSpice and SNAP, resulting responses are confirming the theoretical assumptions.

Electronically-controlled multifunctional current mode filter based on commercially available current conveyors and buffers

Application of commercially available modern functional blocks used for design of analog filters using integrator synthesis method is discussed in this paper. One example of all possible structures of 2nd-order multifunctional filters with current conveyors and followers is chosen and designed. Attention is paid to electronic control of parameters of the filter, sensitivity analysis and computer simulation using OrCAD.

Voltage controlled oscillator using adjustable current-mode selective section with current attenuators

A quite simple adjustable oscillator based on adjustable selective section and lossless integrator is presented in this paper. First order selective section is based on current mode adjustable attenuators employing current-mode multipliers. Characteristic equation, features of electronic adjusting, sensitivities, distortion of output signal and influences of parasitic elements are discussed. Theoretical and estimated assumptions are supported by simulation and experimental results.