Schmitt Trigger with Controllable Hysteresis Using Current Conveyors

Abstract

Abstract-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.

Current conveyor based non-sinusoidal oscillator implementation

“…The Schmitt trigger can be also designed using simple CCIIs [14], however, two active elements have to be used.…”

Design of versatile modulator using CDTAs

“…It comprises of a current diferrencer (Mc1-Mc17) [21] which is followed by transconductance amplifier (Mc18-Mc26). The value of transconductance (g m ) is expressed by (2). …”

Study of impact of voltage gain of comparator on performance of newly designed functional generator

“…Electronic control of parameters in frame of active element [1] is very important for applications that require variable features. Applications that we discuss in this paper focus on triangle and square wave generators based on well-known solution [2] that is formed by loop connection of lossy integrator and comparator with two thresholds/hysteresis (so-called Schmitt trigger) [2]- [4]. Classical approaches employing operational amplifiers [2] are not very feasible because their controllable features are very restricted (only replacement of resistor in integrator by controllable equivalent) and complexity (number of passive elements -at least 3 resistor and floating capacitor) is higher in comparison to solutions utilizing other active devices as will be discussed in further text.…”

“…Research presented in this paper brings new beneficial structure including evaluation of practical impacts of real parameters of the generator. Presented circuit utilizes voltage controllable amplifier(s) for construction of Schmitt comparator [2]- [4] and electronically controllable current conveyor of second generation forming controllable loss-less integrators. Some practical/real properties are quite hidden if only brief and superficial study is done, but these features are important for estimation of expected behavior of application.…”