A STUDY ON SECOND GENERATION CURRENT CONVEYOR. Nemthianhoi Zou P 1, Anil Kumar Gautam 2. & Technology Itanagar, India

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1 Journal of Analysis and Computation (JAC) (An International Peer Reviewed Journal), ISSN Volume XIII, Issue I, January 2019 Nemthianhoi Zou P 1, Anil Kumar Gautam 2 1 Department of Electronics and Communication Engineering 2 Department of Electronics and Communication Engineering North Eastern Regional Institute of Science & Technology Itanagar, India ABSTRACT: Current mode circuit is one beneficial strategy in the field of analog instrumentation design because of its potential for high speed and low voltage. They are a great choice because current is the sole factor determining the working of the circuit. Their major advantage lies when a change in current does not necessarily change the voltage and hence no need to bother about the parasitic capacitance affecting the speed of the circuit. Voltage mode opamp can also be configured as controlled voltage output amplifier but no so as the current mode. OTAs can be ideal for current mode signal processing but it has the defect of being single-ended output, class A output amplifier, open-loop current amplifier and its complexity that it becomes impractical. The current conveyors has replace them by overcoming all of their defects thus gaining popularity in the field of analog design. This paper provides the fundamentals of current conveyors and design of second generation current conveyor in detail. Keywords: Current mode circuit, Voltage mode, Amplifier, OTA, First generation current conveyor, Second generation current conveyor [1] INTRODUCTION The current conveyors were first introduced by A Sedra and K.C Smith [1] as a part of YM.Tech thesis in the year Since then it has developed from first generation current conveyor to second and then to third generation current conveyor. In a current conveyor or CC, current is conveyed between two ports of different impedance levels. CC I was first implemented with elementary common-base transistor [2]. V Ix Y X CC Z IZ Figure: 1. Black box representation of CC. From Figure 1, if input terminal Y is applied a voltage V, the same will appear at the other end X. Similarly when a current I is forced at X, it is conveyed to Y which is later being Nemthianhoi Zou P and Anil Kumar Gautam 1

2 supposedly passed on to Z at high impedance like a current source. Meanwhile the current I through X, has fixed which becomes independent of Y and therefore appears like a short circuit whereas on the other hand Y side is an open circuit. The hybrid characteristics of X-Y terminal with Z grounded is as given Also the hybrid characteristics of X-Z terminal with Y grounded is as given The overall hybrid characteristics of CC I is [2] SECOND GENERATION CURRENT CONVEYORS The second generation current conveyor or simply CC II has the same current conveying techniques as CC I but with different and more versatile terminal characteristics [3]. VY Vx Y X CC II Z IZ Figure: 2. Black box representation of CC II The terminal characteristics of CC II are Nemthianhoi Zou P and Anil Kumar Gautam 2

3 Journal of Analysis and Computation (JAC) (An International Peer Reviewed Journal), ISSN Volume XIII, Issue I, January 2019 The operation of CC II is somewhat similar to CC I in the sense that the voltage applied at one of the input Y appears at X. The input is given at the high input impedance terminal Y which is reflected at the low input impedance node X using the concept of virtual short circuit and therefore conveys the current I efficiently to Z with minimum resistance. The current at Z can be ±I depending on the polarity of Z. Hence the CC II s are of two types CC II- and CC II+. If the current flowing in the terminals X and Z are of opposite direction then they are called negative CC II and positive if otherwise. [3] CHARACTERISTICS OF THE SECOND GENERATION CURRENT CONVEYOR Input Impedance Ideally the CC II has high input impedance at Y i.e R Y = 0 and a very low impedance at X i.e R X = ꝏ. This enables to reduce the load based on the driving current. Bandwidth The CC II usually have high bandwidth. It can be further increased by applying feedback to it. Slew rate The slew rate of CC II are ideally high because of the current mode nature. The output of a transistor in current mode is in saturation and hence the charging and discharging of the current depends on the current strength which is not in the case of voltage mode. Gain Current conveyors are usually unity gain current amplifiers and unity gain voltage amplifiers. The unity gain renders to the fact that the current or voltage at the input is ideally conveyed to the output. Operation mode CC II can be realized in transfer function in voltage mode [4] as well as current mode depending on the required application. Realization The CC II can be realized using current mirrors or operation amplifiers [5]. The current mirror topology is used in high frequency applications due to the parasitic poles by low impedance. The problem lies in the NMOS when the threshold voltage is raised as it causes body-effect where the source is at high potential and the bulk at the VSS. It also limits the use of cascade. Opamps are favorable for low frequency applications. They are widely used for low voltage application. Using rail-to-rail topology, rail-to-rail current conveyor can be designed but the disadvantage lies in the poor current conveying as compared to current mirror method. Nemthianhoi Zou P and Anil Kumar Gautam 3

4 [4] APPLICATIONS OF SECOND GENERATION CURRENT CONVEYOR The second generation current conveyor find its application in area of network synthesis like voltage follower, voltage controlled current source, current follower, current controlled current source and analog computation such as current amplifier, current derivator, current integrator, current adder, voltage amplifier, voltage derivator, voltage adder, voltage integrator. Network synthesis Figure: 3. Voltage follower Figure: 4. Voltage controlled current source Figure: 5. Current follower Figure: 6. Current controlled current source Analog computation Nemthianhoi Zou P and Anil Kumar Gautam 4

5 Journal of Analysis and Computation (JAC) (An International Peer Reviewed Journal), ISSN Volume XIII, Issue I, January 2019 Figure: 7. Current amplifier Figure: 8. Voltage amplifier Figure: 9. Voltage derivator [6] CONCLUSION Conventional voltage mode based circuits like Opamp have failed to produce effective results and thus came the need for current conveyors. Current conveyors are expanding in their applications from wideband current measuring device to current conveyors II in instrumentation and computation devices. CC II is more versatile than the previous type because of its ability to convey current through the low impedance node and thus is more efficient in conveying current to the output terminal. Nemthianhoi Zou P and Anil Kumar Gautam 5

6 REFERENCES [1] A.S Sedra, G.W Roberts and F John, The Current Conveyor history, progress and new results, IEE Proceedings of ISCAS, Vol. 137.Pt, G, No.2 April [2] K.C Smith and A Sedra, The Current Conveyor a new circuit Building Block Proceedings of IEEE, August [3] K.C Smith and A Sedra, A second-generation current conveyor and its application IEEE transactions on Circuit theory, February [4] David Moro Frais, Design and application of CMOS current conveyors Dissertation to program of Electronic Science, [5] Roman Prokop and Vladislav Musil, Current Conveyor CC II as the most Versatile Analog Circuit Building Block, Annual Journal of Electronics, Nemthianhoi Zou P and Anil Kumar Gautam 6