A Current-Mode Wheatstone Bridge Employing Only Single DO-CDTA Chaiya Tanaphatsiri Department of Telecommunication technology, Faculty of Engineering, Rajamangala University of Technology Srivijaya Songkhla, 90000, Thailand Tel: +66-7-431-7169 Fax. +66-7-431- 7195 Email: chaiya_32@hotmail.com Winai Jaikla Electric and Electronic Program, Faculty of Industrial Technology, Suan Sunandha Rajabhat University Dusit, Bangkok, 10300, Thailand Tel: +66-2-243-2240 Ext. 317, Fax: +66-2-241-5935 Email: winai.ja@ssru.ac.th Montree Siripruchyanun Department of Teacher Training in Electrical Engineering, Faculty of Technical Education, King Mongkut’s University of Technology North Bangkok Bangkok, 10800, Thailand Tel: +66-2- 913-2500 Ext. 3328 Fax. +66-2-587-8255 Email: mts@kmutnb.ac.th Abstract— This article proposes a topology of current-mode improved Wheatstone bridge based on dual-output current differencing transconductance amplifier (DO-CDTA). The features of the proposed configuration are that: magnitude of output signal can be controlled via the input bias currents; the proposed circuit is low temperature sensitive, the circuit description is very simple. The circuit performances are depicted through PSPICE simulations, they show good agreement to theoretical anticipation and provide ability to measure small resistance changes at a wide range of frequency (more than 60MHz). The power consumption is approximately 4.55mW at ±1.5V supply voltages. I. INTRODUCTION For many years, Wheatstone bridge is used for checking small resistance changes. Consequently, it is useful for instrumentation, sensing temperature, strain, pressure and dew point humidity [1-2]. The conventional voltage-mode Wheatstone bridge consisting of 4 resistors is shown in Fig. 1(a). Subsequently, a method based on the circuit duality concept has been modified to develop a current-mode Wheatstone bridge (CMWB) by Azhari and Kaabi [3], they have claimed that it can overcome several drawbacks of the Wheatstone bridge. These are reducing circuit elements, superposition principle and common mode cancellation. This is called AZKA cell [3], shown in Fig 1(b). However, by inspective survey, two different topologies to implement a CMWB have been proposed. The first one uses two second- generation current conveyors (CCIIs), therefore the accuracy is limited by the tolerance of intrinsic resistances of the CCIIs, which is low, the linearization is unavoidably needed. The second approach to implement a CMWB using operational floating current conveyors (OFCCs), has a higher accuracy, as the output current does not depend on the intrinsic resistance. However, there is no reduction of the sensing resistors, as the second approach uses two excess resistors. Recently, a new CMWB topology using OFCCs has been introduced [4]. It has a smaller area for fabrication because it reduces the sensing passive elements, and uses only two resistors without degradation in the performance. Also, it uses the principle of superposition without adding any signal conditioning circuitry. Unfortunately, it confronts several drawbacks such as circuit complexity, temperature dependence, lack of electronic controllability to adapt in an automatic control system. Although, an appropriately controllable amplifier can be added to achieve adjustable gain, the offsets might be a much increased. By using the principle of AZKA cell, Jaikla and Siripruchyanun have proposed the voltage and current-mode Wheatstone bridge [5]. The features of these circuits are electronic controllability and low temperature sensitivity. Unfortunately, the circuits consist of many different active elements (2 CCCIIs and 1 CDBA for voltage-mode, 1 CDTA and 1 CCCII for current-mode) which is not appropriate for realizing in a monolithic chip. The aim of this paper is to introduce a configuration of current-mode Wheatstone bridge. The proposed topology enjoys several features as follows: the proposed circuit is temperature-insensitive, electronic controllable, uncomplicated of circuit detail. In addition, the proposed topology has a much-improved common-mode cancellation and can work with a wide range of frequencies which is an important property to suppress any unwanted common-mode signal or noise at a high range of frequencies. So, the proposed circuit has a high accuracy and employs only single DO- CDTA. The mentioned properties are confirmed by PSPICE simulation. The proposed topology is very suitable for the measurement of small resistance changes. 1494 978-1-4244-2342-2/08/$25.00 ©2008 IEEE.