An Ultra-Linear Piezo-Floating-Gate Strain-Gauge for Self-Powered Measurement of Quasi-Static-Strain

In this paper we describe a self-powered sensor that can be used for in-vivo measurement of the quasi-static-strain and also for in-vivo measurement of the L₁ norm of the strain signal. At the core of the proposed design is a linear floating-gate injector that can achieve more than 13 bits of precision in sensing, signal integration and non-volatile storage. The injectors are self-powered by the piezoelectric transducers that convert mechanical energy from strain-variations into electrical energy. A differential injector topology is used to measure the quasi-static strain by integrating the difference between the L₁ norm of the piezoelectric signal generated during the positive and negative strain-cycles. The linear floating-gate injectors are integrated with charge-pumps, digital calibration circuits and digital programming circuits to form a system-on-chip solution that can interface with a standard bio-telemetry platform. We demonstrate the proof-of-concept self-powered measurement of quasi-static strain and L₁ norm of the strain signal using sensor prototypes fabricated in a 0.5- μm standard CMOS process and validated using a bench-top biomechanical test setup.