The Intersil HI7191 is a monolithic instrumentation， sigma delta A/D converter which operates from ±5V supplies. Both the signal and reference inputs are fully differential for maximum flexibility and performance. An internal Programmable Gain Instrumentation Amplifier （PGIA） provides input gains from 1 to 128 eliminating the need for external pre-amplifiers. The on-demand converter auto-calibrate function is capable of removing offset and gain errors existing in external and internal circuitry. The on-board user programmable digital filter provides over 120dB of 60/50Hz noise rejection and allows fine tuning of resolution and conversion speed over a wide dynamic range. The HI7190 and HI7191 are functionally the same device， but the HI7190 has tighter linearity specs. The HI7191 contains a serial I/O port and is compatible with most synchronous transfer formats including both the Motorola 6805/11 series SPI and Intel 8051 series SSR protocols. A sophisticated set of commands gives the user control over calibration， PGIA gain， device selection， standby mode， and several other features. The On-chip Calibration Registers allow the user to read and write calibration data.