A CMOS Smart Thermal Sensor for Biomedical Application

Ho-Yin LEE  Shih-Lun CHEN  Ching-Hsing LUO  

IEICE TRANSACTIONS on Electronics   Vol.E91-C   No.1   pp.96-104
Publication Date: 2008/01/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e91-c.1.96
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Organic Molecular Electronics
auto-calibration,  CMOS thermal sensor,  deep N-well,  sigma delta modulator,  vertical bipolar transistor,  

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This paper describes a smart thermal sensing chip with an integrated vertical bipolar transistor sensor, a Sigma Delta Modulator (SDM), a Micro-Control Unit (MCU), and a bandgap reference voltage generator for biomedical application by using 0.18 µm CMOS process. The npn bipolar transistors with the Deep N-Well (DNW) instead of the pnp bipolar transistor is first adopted as the sensor for good isolation from substrate coupling noise. In addition to data compression, Micro-Control Unit (MCU) plays an important role for executing auto-calibration by digitally trimming the bipolar sensor in parallel to save power consumption and to reduce feedback complexity. It is different from the present analog feedback calibration technologies. Using one sensor, instead of two sensors, to create two differential signals in 180phase difference input to SDM is also a novel design of this work. As a result, in the range of 0 to 80 or body temperature (375), the inaccuracy is less than 0.1 or 0.05 respectively with one-point calibration after packaging. The average power consumption is 268.4 µW with 1.8 V supply voltage.