Current-Controlled CCTA-Based Novel Current- Mode Schmitt Trigger and Its Application Montree Siripruchyanun Department of Teacher Training in Electrical Engineering, Faculty of Technical Education, King Mongkut’s University of Technology North Bangkok, Bangsue, Bangkok, 10800, THAILAND Tel: +66-2- 913-2500 Ext. 3328 Fax. +66-2-587-8255 Email: mts@kmutnb.ac.th Abstract- This article presents a new current-mode Schmitt trigger based on MO-CCCCTA (Multiple-output current controlled current conveyor transconductance amplifier). The circuit description is very simple, its construction consists of only single MO-CCCCTA, without any external passive element. The hysteresis and amplitude of the output current can be tuned independently/electronically by input bias currents. With mentioned features, it is very suitable to realize in a monolithic chip. The application as a square-wave generator is given here to display the usefulness of the presented Schmitt trigger. The PSPICE simulation results are depicted, and agree well with the theoretical anticipation. The maximum power consumption is approximately 92.5μW at ±1.5V power supply voltages. I. INTRODUCTION A Schmitt trigger has been proposed for the first time by Otto Schmitt in 1938 [1]. Its application is to reduce the noise effect in triggering devices and analog to digital conversion [2]. Additionally, it is principal block in a square wave generator, pulse width modulator, monostable multivibrator, and etc. From our survey, we found that several implementations of the Schmitt triggers employing different high-performance active building blocks such as op-amp [3]. Its high frequency performance of this circuit is restricted by signal bandwidth and slew rate of the op-amp. In addition, its frequency and magnitude can not be electronically controlled, the magnitude of output signal also depends on supply voltages. Latterly, the Schmitt triggers based on operational transconductance amplifiers (OTAs) [4] and current conveyors [5] have been reported. Unfortunately, they suffer from excessive use of passive elements and/or active elements. Especially, they operate in voltage-mode. The current–mode technique is ideally suited to this purpose more so than the voltage-mode type. Presently, there is a growing interest in synthesizing current-mode circuits because of more their potential advantages such as larger dynamic range, higher signal bandwidth, greater linearity, simpler circuitry, and lower power consumption [6-9]. Recently, the Schmitt triggers based on current-mode technique and high- performance active building blocks, such as current differencing transconductance amplifier (CDTA) [10] and current controlled CDTA (CCCDTA) [11] have been also introduced. However, they still suffer from excessive use of the passive elements [10-11] and lack of electronically independent controllability of threshold and output level [11]. These factors are desirable for modern electronic circuit design. The current conveyor transconductance amplifier (CCTA) is a reported active component, especially suitable for a class of analog signal processing [12]. The fact that the device can operate in both current and voltage-modes provides flexibility and enables a variety of circuit designs. In addition, it can offer advantageous features such as high-slew rate, higher speed, wide bandwidth and simple implementation [12]. However, the CCTA can not be controlled by the parasitic resistance at x x R port so when it is used in some circuits, it must unavoidably require some external passive components, especially the resistors. This makes it not appropriate for IC implementation due to occupying more chip area, high power dissipation and without electronic controllability. Recently, the current-controlled CCTA (CCCCTA) [13] has been proposed, it was proved that it can overcome the mentioned limitations of the CCTA. The purpose of this paper is to introduce a novel current mode Schmitt trigger, emphasizing on use of MO-CCCCTA (a modified version of the CCCCTA). The features of the proposed circuits are that: the circuit description is very simple, its construction consists of only single MO-CCCCTA, without any external passive element: the hysteresis and amplitude of the output current can be tuned independently/electronically, it can be applied in an automatic control via a microprocessor [7]. The PSPICE simulation results are also shown, which are in correspondence with the theoretical analysis. The application of the proposed Schmitt trigger as a square-wave generator is included. II. CIRCUIT CONFIGURATION A. Basic Concept of MO-CCCCTA Since the proposed circuit is based on MO-CCCCTA, a brief review of the MO-CCCCTA is given in this section. Generally, the MO-CCCCTA properties are similar to the conventional CCTA, except that the CCCCTA has finite input resistance x R at the x input terminal. The parasitic resistance can be controlled by the bias current 1 B I as shown in the following equation 1 2 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 y y x x x z o m o o m o z I V V R I I V g I V g I V , (1) 416 2008 International Symposium on Communications and Information Technologies (ISCIT 2008) 978-1-4244-2336-1/08/$25.00 © 2008 IEEE