Moshe Gerstanhaber @ edn.com provides an simple ADC interface using instrumentation amplifier IC.
Real-world measurement requires the extraction of weak signals from noisy sources. High common-mode voltages are often present even in differential measurements. The usual approach to this problem is to use an op amp or an instrumentation amplifier and then perform some type of lowpass-filtering to reduce the background noise level.
Simple circuit provides precision ADC interface – [Link]