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Vol. 229, Issue 1, January 2019, pp. 61-67




Using the Non-linear Behavior of the Brokaw Bandgap Voltage Reference Cell
to Linearize Resistance Temperature Detectors (RTD)

1, 2 Pedro Carvalhaes-Dias, 2 Ivan P. Ferreira, 1, 2 Luίs F. C. Duarte, 3 Flávio J. O. Morais and 2 J. A. Siqueira Dias

1 Paraná Federal University of Technology, Av. A. Carazzai, Cornélio Procópio, 1640, PR, Brazil
2 Department of Semiconductors, Instrumentation and Photonics, School of Electrical and Computer Engineering - Unicamp, Av. Albert Einstein, 400, Campinas, SP, Brazil
3 Faculty of Sciences and Engineering, UNESP, R. D. Costa Lopes, 780, Tupã, SP, Brazil
2 Tel.: +55 19 3521-4901, fax: + 55 19 3521-4896

2 E-mail: siqueira@demic.fee.unicamp.br


Received: 30 November 2018 /Accepted: 31 December 2018 /Published: 31 January 2019

Digital Sensors and Sensor Sysstems


Abstract: Resistance temperature detectors (RTD) present second and third order non-linearities, and a linear signal processing circuit which converts the voltage on a Pt-100 RTD to an output voltage with 10 mV/oC presents a maximum non-linearity error of 1.07 oC (10.7 mV) in the 0 to 85 oC temperature range. These non-linearities can be corrected digitally, but there are applications where a simple analog linearization can be used with advantages, as in the case of a direct interface of an RTD sensor with a 4-20 mA current loop transducer. The intrinsic curvature of the Brokaw bandgap voltage reference cell, caused by the non- linear variation of the bipolar transistor's VBE with temperature, can be used to create a compensation voltage that can be used to reduce the non-linearity of the signal processing circuit of resistance temperature. A discrete Brokaw bandgap reference cell using a bipolar analog array LM3046 and a high precision op-amp was designed, and the calculated values of the final circuit indicate that the non-linearity of the signal conditioning circuit of a Pt-100 RTD is reduced by one order of magnitude (down to approximately 0.14 oC) in the 0-85 oC temperature range.


Keywords: RTD, Bandgap curvature, Brokaw cell, Linearization, Temperature sensors.


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