A digital output monolithic temperature sensor for invasive applications

Measurement of temperature inside the human body is of great importance in many applications. Temperature sensors having small size, good reproducibility and high resolution together with low power consumption are needed. In this paper we present a silicon temperature sensor fabricated in a standard CMOS-technology with integrated bias, amplification and A/D-conversion. The sensor is based on two forward biased pn-diodes with different areas and current densities. A temperature coefficient of 0.43 mV/K before amplification is obtained. The resolution in a temperature range from 10xC to 50xC is better than 1 x E-3 and a reproducibility of 0.07xC is achieved. The sensor signal is amplified by using switched -capacitor circuitry and converted into a pulse width modulated signal by a single-slope converter.