A 40-μA/channel compensated 18-channel strain gauge measurement system for stress monitoring in dental implants

This paper presents an autonomous monitoring system ASIC, which is capable of measuring and compensating 18 strain gauges simultaneously. This sensor interface is implemented in a 0.7-mum CMOS technology and includes a proportional to absolute temperature (PTAT)-current reference, an 8-bit digital-to-analog converter together with a digital interface for multigauge nulling, a switched-capacitor (SC) instrumentation amplifier, an SC sample-and-hold (S/H), and a 9-bit successive approximation analog-to-digital converter. The total chip consumes a mere 40 muA/channel (at 3.1 V) and allows for sampling of each individual strain gauge channel at a sampling rate of 111 Hz with a 20-mustrain accuracy. The measurement system presented is a part of an autonomous data logger, which is integrated in a dental prosthesis.