Conditioning circuit for temperature and strain measurement

Abstract

The objective of this thesis is to develop an integrated conditioning circuit for simultaneous measurement of temperature and straining utilizing a technique which uses fewer connecting wires (i.e. wires from sensor to readout instrument) than conventional techniques. The technique was originally developed at NASA, but has been slightly modified here to obtain the best possible results from the conditioning circuit. The core of the conditioning circuit is formed by a precision switched capacitor instrumentation amplifier operating on a +/-6 V supply. The use of double correlated sampling technique achieves high power supply rejection, low dc offset and low 1/f noise voltage. Matched circuit components in a fully differential configuration along with bottom plate sampling minimize errors from switch channel charge injection. Very high common mode rejection is obtained by using dynamic common mode feedback. The instrumentation amplifier is designed to have an ability for resolving a few microvolts of difference at its input. Bandgap reference technique has been used to incorporate a temperature insensitive current source on the chip. An on-chip clock generator is also built for generating timing signals required for the operation of the switched capacitor circuit. The signal conditioning circuit is designed and fabricated using a 2.0 1-t n-well, double poly CMOS process.