Below ground measurements with a single supply delta-sigma A/D converter

Temperature, the most commonly measured physical property, is usually measured with ground based thermocouples that produce signals both above and below ground. This high accuracy, single-supply, converter introduces a synchronized substrate pumping technique which enables the measurement of below ground signals without corruption by substrate noise. Using a 4th order delta-sigma (DS) modulator, this 20 bit converter delivers an SNR of 108.67 dB and S/D of 110.19 dB, while consuming only 7.194 mW. An integrated instrumentation amplifier is used to get the signal to a level acceptable by the DS. A digital filter is used to eliminate the DS quantization noise. The whole chip is controlled via a 3 wire serial interface.