Performance evaluation of CCOs for the optimization of low-power pressure-based implantable wireless systems

Abstract

Implantable biomedical devices intended for remote follow-up of Cardiovascular Diseases (CVD) are often based on MEMS pressure sensors and the corresponding CMOS electronics, which are responsible for powering, signal conditioning and data transmission. This kind of heterogeneous systems achieves reduced dimensions and consumption by monolithic integration on the same silicon substrate. The objective of this work is to analyze and fully characterize several Capacitor-Controlled Oscillator (CCO) topologies that can be used for the aforementioned implantable applications, by comparison of their most relevant performance parameters. The results will allow the design optimization of low-power wireless implants, aimed at a future development of embedded systems with real-time data acquisition. Five topologies have been chosen for the evaluation: a standard ring oscillator; a current-starved ring oscillator; a Lee-Kim fully-differential oscillator; a coupled Sawtooth oscillator, and a modified Sawtooth oscillator designed for CCOs biased by a ramped voltage signal. Comprehensive simulations allowed the estimation of the output frequency, percentage tuning range, maximum linearity error, phase noise and power consumption for each design, as well as a Figure of Merit, for every CCO. For the calculation of these performance metrics, the impact of biasing circuits and different tuning strategies has also been considered.