Multiparameter sensor interface circuit for microsystems

Abstract

For multiparameter sensor environment, where various types of sensors are used such as implantable devices and mobile health care, a versatile version of analog front-end is suggested. The proposed analog front-end adopts capacitive, resistive, and voltage type interfaces especially targeted for microsystems. In order for the interface circuits to have linear conversion characteristic and large conversion gain, the most attractive topologies are adopted: switched capacitor integrator, current source, and fully differential amplifier. Each interface has an excellent linearity ($R^{2}$ > 0.999) with respect to the variation of C, R, and V. For each interface, the maximum conversion gains at output are: 194.56 mV/fF for the ca-pacitive interface, $6.26 V/k \Omega$ for the resistive interface, and 236 V/V for the voltage ampli-fier. Besides the basic interfaces, the analog front-end is designed to cancel 1/f noise and offsets. On simulation, the AFE suppresses 1/f noise at 10 Hz by 30 dB for buffers and 44 dB for fully differential amplifiers based on correlated double sampling scheme. Offset is canceled with two separate schemes: signal level shifting and amplifier balancing. Based on the schemes, offset voltage is suppressed with 0.6 mV resolution

this prevents amplifier from saturating even at the maximum gain and ensures pure sensor signal to have large room for swing. The AFE operates at 2.5 V supply, and is designed using TSMC $0.25 \mu m$ CMOS technology. Overall power consumption is no more than 4 mW.