Cost-effective and compact analog compensation method of thermal drift of implantable piezoresistive blood pressure sensors

Abstract

Implantable pressure sensors are important tools of preclinical research activity in laboratories. Unfortunately, their use is limited by cost, autonomy and temperature-related drifts. Cost and ease of use depend on several parameters, in particular battery life and miniaturization required to be able to implant animals and monitor them over time that is long enough to be physiologically relevant. While thermal drifts inherent in implantable sensors due to animals’ body temperature variation vary depending on their operating principe. Reduction of thermal drift and energy consumption and overall miniaturization. The blood pressure sensor studied is based on a Honeywell NPB030 piezoresistive probe chosen due to its low cost and compactness. We look for reducing its thermal drifts over temperature range [34 °C–39 °C] and pressure range [0 - 300 mmHg]. With a classical conditioning circuit, the sensor's overall relative drift is 3,2%/°C (13.4 mV/°C/420 mV), resulting from two contributions, one of 2.7%/°C (0.1 mV/°C/3.6 mV) due to the piezoresistive probe alone, another of 0.1% (0.98 mV/°C/916 mV) due to the conditioning circuit alone. An NPN transistor is added in series with the Wheaston Bridge formed by the piezoresistors of the pressure probe to correct the thermal drift. Thanks to optimization of bias resistors of the transistor using Cadence/Pspice, the measured overall thermal drift of the compensated sensor is reduced to 0.09%/°C (0.371 mV/°C/405 mV), in very good agreement with simulation. It's worth noting that the optimization is made possible due to our original method to determine the value of each piezoresistor in the Wheaston Bridge. Our approach proves effective to reduce thermal drift of the studied pressure sensor. Additional space required, cost and consumption will be very low. This method should be assessed and validated with CMS components.