Aryesh Amar

A DC measurement IC with 130 nV/sub pp/ noise in 10 Hz

A CMOS DC measurement IC surpasses the noise performance of prior-art integrated systems. The instrumentation amplifier surpasses commercially-available stand-alone inamp solutions in 0.1 to 10 Hz noise performance. It is targeted for bridge transducer measurements where signal levels are typically of the order of a few mV. Low noise is crucial at these signal levels. In prior-art, integrated DC measurement systems the wideband noise of the instrumentation amplifier is sampled directly without anti-aliasing and thus noise performance is sacrificed for a simpler interface between amplifier and modulator. This article shows a block diagram of the IC consisting of a programmable gain instrumentation amplifier followed by a 4th-order /spl Delta//spl Sigma/ modulator, a programmable decimation filter, and a 3-wire serial interface. The inamp uses the multipath feedforward architecture that offers flexibility in low frequency applications because it separates the low frequency signal path from the high frequency path designed for stability. The architecture is modified to reduce the offset introduced by the second stage of the amplifier. It is also modified according to the reduced bandwidth requirements in the DC measurement application. Special attention is given the chopper stabilization.

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.