Ultra low power capacitive sensor interface with smart energy management

The drive towards an intelligent environment will give the first impulse to several sensor applications such as intelligent prostheses, sport evaluation, observation of livestock, etc. Conventional interfaces are tailored towards the requirements of one of these applications. This leads to a high design cost for these autonomous sensor systems. An ultra low power generic sensor interface offers an attractive solution for this problem. It allows us to adapt the front-end after it is taken in use. Moreover, a generic sensor interface is capable of reading out several sensors. This paper presents a Generic Sensor Interface Chip (GSIC), which can read out a broad range of capacitive sensors. The GSIC is designed as a complete system in order to optimize it for ultra low power consumption. It contains Capacitance-to-Voltage converters, a Switched Capacitor amplifier, an Analog-to-Digital Converter, oscillators, clock generation circuits and a reference circuit. The total system consumes merely 38 μA in operational mode with a 3 V supply. The duty cycle management allows us to adapt the energy consumption according to the accuracy and speed requirements of the application. This results in an average current consumption of 1.3 μA for an autonomous sensor application with 5 Hz bandwidth and 8-bit resolution.