Towards Energy-Efficient CMOS Integrated Sensor-to-Digital Interface Circuits

The ever increasing demand for improved autonomy in wireless sensor devices, drives the search for new energy-efficient sensor interface topologies in CMOS technology. Recently, time-based conversion has gained a lot of interest due to its high potential to implement highly-digital circuitry. While voltage-based analog integrated circuits suffer from the decreased supply voltage and voltage swing in highly-scaled CMOS technologies, time-based processing takes advantage of the increased timing resolution. However, how do these time-based sensor interface circuits compare to their amplitude-based counterparts fundamentally? To answer this question, theoretical limits are derived in this chapter for both implementations, which shows that the sensor itself is actually the dominant factor in limiting the achievable energy efficiency. Time-based topologies, however, enable the implementation of highly-digital interfaces, which are scalable, area-efficient and have low-voltage potential. These observations are illustrated with several practical designs.