Converters dedicated to long-term monitoring of strain gauge transducers

This paper presents two new strain gauge bridge-to-pulse position modulation (PPM) converters. They have been developed in 2-/spl mu/m BiCMOS technology. The first one uses a chopper amplifier and a voltage-to-time converter associated in a feedback loop. This topology mainly exhibits an automatic offset cancellation capability, a ratiometric transfer function, and 10-b accuracy. The second one is a voltage-to-frequency converter using the switched-capacitor (SC) technique. It is an optimized version in terms of size minimization and noise rejection. Furthermore, a special RF transmitter has been designed in order to send the data from an intracorporal sensing and conditioning circuitry to an external computer dedicated to data analysis. Moreover, these converters are insensitive to offset drifts and are well suited for long term monitoring of orthopedic implants used for the treatment of bone fractures.