A novel current conveyor‐based Schmitt trigger and its application as a relaxation oscillator

Synthesis of active inductors using SFG stamps

MOS-C realizations of the Kerwin–Huelsman–Newcomb (KHN) circuit using the commercially available Voltage Operational Amplifier (VOA) and the Current Feedback Operational Amplifier (CFOA) are reviewed in this paper. Additional MOS-C KHN realizations using the Operational Transresistance Amplifier (OTRA) and the Differential Current Voltage Conveyor (DCVC) are also included. MOS-C realizations of the KHN circuit using CMOS operational amplifier, CMOS current feedback operational amplifier and CMOS operational transresistance amplifier are also given.Spice simulation results using 0.18 CMOS technology model from MOSIS are included together with detailed comparison tables to demonstrate the differences between MOS-C KHN circuits using both of the commercially available active building blocks and CMOS integrated building blocks. A comparison with the Gm-C KHN circuit is also included.

ABSTRACTIn this paper, we present an exact analysis of finite gain inverting voltage amplifiers using current feedback operational amplifiers (CFOA) for use as stand-alone amplifiers or for being used in second-order active resistance capacitance (RC) filters such as Tow–Thomas biquads. The proposed circuits require one or two additional CFOAs/resistors/capacitors. The effect of finite output impedance at z terminal, input resistance at x terminal, and current mirror pole of the CFOA are studied. The circuits considered have been simulated using PSPICE using a behavioural macro-model of the CFOA as well as that of a practical CFOA AD 844.

Improved realization of canonical Chua's circuit with synthetic inductor using current feedback operational amplifiers

-This paper presents the design of a sinusoidal, triangular, and square wave generator using a high speed current feedback operational amplifier (CFOA). A macro model for the CFOA is developed as well. The frequency of oscillation in all cases are derived and compared with the simulated values. The achieved frequency of oscillation for sinusoidal wave is 9.4 MHz to 15 MHz and the achieved frequency of oscillation for the triangular/rectangular wave is 6.75 MHz to 59.5 MHz. The advantage of using the current feedback operational amplifier is to get higher frequency of sinusoidal, triangular, and square wave.

Current feedback operational amplifiers: a tutorial In a didactic approach, the amplifying properties of an inverter stage using a current feedback operational amplifier (COA) and one using a voltage feedback operational amplifier (VOA) are compared. Then, following a discussion of COA modelling, the frequency and transient responses of a COA non-inverter stage are analysed.

A novel topology for realizing voltage-mode (VM) full-wave rectifier/sinusoidal frequency doubler based on current feedback operational amplifiers (CFOAs) and n-channel metal-oxide semiconductor (NMOS) transistors is proposed in this study. The proposed full-wave rectifier structure employs two CFOAs and three enhancement-mode NMOS transistors. With a slight modification, the sinusoidal frequency doubler circuit can be adopted from the full-wave rectifier circuit by replacing a grounded resistor instead of one of the NMOS transistors. Both of the proposed circuits enjoy low output and high input impedance properties which make them convenient for cascading easily with other VM circuits without needing any extra buffer circuits. No passive component matching conditions are needed. The proposed circuits are simulated by using SPICE program to verify the theoretical analysis.

In recent years, many articles came out where one could find the analysis of oscillatory systems of electric sinusoid signals generators with amplifiers called CFOA—current feedback operational amplifiers. As a rule, the analysis of such systems is made by applying mathematical modeling methods on the basis of the amplifier linear model, which does not allow estimating advantages and disadvantages of the systems realized with those amplifiers in comparison with classical systems. A nonlinear model of a current feedback operational amplifier (CFOA) is introduced in the paper; nonlinearity of “current mirror” is reflected in the form of current double limiting. The analysis of two known oscillatory systems has been carried out with the use of this non-linear model. Dependence between current limiting level, output voltage amplitude, and maximum oscillation frequency has been obtained. The paper shows that output current limiting under current output connection of capacitive load reduces frequency range and output voltage amplitude considerably and increases harmonic distortions in comparison with classical oscillatory systems. The research done has found that the application of new amplifiers does not give considerable advantages to the oscillatory systems with CFOA.

The voltage feedback operational amplifier (VFOA) and the current feedback operational amplifier (CFOA) are the main voltage type output opamps currently used in electronics. The VFOA is a combination of an operational transconductance amplifier (OTA) used as an input stage and an output voltage buffer (VB). In this paper, the CFOA is described as a combination of an operational transconductance conveyor (OTC) used as an input stage and with an output voltage buffer. Two similar CMOS architectures are then defined, analysed and simulated in order to provide some elements of comparison. Results, from a typical CMOS 0.35μm transistor parameters, show the role of compensation capacitances in boosting the frequency performances of the non-inverting amplifier.

In this paper, a method is proposed to realize the grid multi-scroll chaotic system with the current feedback operational amplifier (CFOA). Firstly, nonlinear circuit is designed based on the CFOA. Then the grid multi-scroll chaotic circuit is designed and relevant circuit parameters are calculated. Finally circuit simulation is conducted, and the results show that the circuit has a higher central frequency, needs less components, and possesses simpler circuit structure, good frequency characteristic and port characteristic of the CFOA.

Low-voltage subthreshold CMOS current mode circuits: Design and applications

Active elements working in the current or mixed mode are still attractive for the design of analog functional blocks. The current conveyor (CC) was defined already in 1968. This paper deals with hysteresis comparators using second generation current conveyor. The comparator is basically a pulse circuit. In these circuits, the maximum rate of change in the output voltage is required during switching from one state to another. In comparators with operational amplifiers the switching time is given by the slew rate of the operational amplifier used, which is not too high. If a current conveyor is used, the time of switching the comparator gets shorter. The comparator is capable to operate at a higher frequency bands and if it is used, for example, in converters, a higher operating frequency can be reached. The connection of an inverting and a non-inverting comparator with adjustable hysteresis is shown as a practical implementation. Using the AD844, results of experimental measurements are presented that confirm the theoretical assumptions and the results of computer simulation.

In this paper, a circuit technique to extend the measuring range of a linear variable differential transformer (LVDT) is proposed. The transfer characteristic of the LVDT contains the odd function form of the cubic polynomial. Therefore, the measuring range of a commercial LVDT is linear in a narrow range compared to its physical dimensions. The wide measuring range of the LVDT requires a large structure of the LVDT, which increases the scale and the cost of the measurement system. The measuring range of the LVDT can be linearly extended to the maximum of the stroke range using the proposed technique. The realization of the proposed technique is based on the use of the hyperbolic sine (sinh) function of the electronic circuit building block, named the class AB bipolar amplifier. The class AB bipolar amplifier can be obtained by the current feedback operational amplifier (CFOA). The circuit of the proposed technique requires two CFOAs and an operational transconductance amplifier (OTA) as the active devices and all devices used in the proposed technique to synthesize the sinh function are commercially available. The proposed technique exhibits an ability to compensate for the nonlinear characteristic of the LVDT without digital components. The proposed technique is attractive in terms of its simple circuit configuration, small size, and low cost. The linear range extension of the LVDT used in this paper is significantly increased with a maximum error of about 18.3 μm of 6.2 mm at the full stroke range or the full-scale percentage error of about 0.295%. The results indicate that the proposed technique provides excellent performance to extend the measuring range of the LVDT without modifying the LVDT structure.

A five-port general purpose analogue building block, termed as an operational floating current conveyor (OFCC), is described. The OFCC combines the features of a current feedback (CFB) operational amplifier, second generation current conveyor and operational floating conveyor (OFC). A simple implementation scheme of the OFCC is described and its terminal operational characteristics are used to yield a working model. The OFCC is then used as a single block to realize the current conveyors (CCII+ and CCII-). Experimental results are presented and show good behavioral agreement with simulation results.

A new five-port general purpose analogue building block, termed as an operational floating current conveyor (OFCC), is described. The OFCC combines the features of current feedback (CFB) operational amplifier, second generation current conveyor and operational floating conveyor (OFC). A simple implementation scheme of the OFCC is described and its terminal operational characteristics are used to yield a working model. The OFCC is then used as a single block to realize the four main amplifier types and the current conveyors (CCII+ and CCII-). Computer simulation results are presented and discussed. >