The AD7631 is an 18-bit， charge redistribution， successive approximation register （SAR）， architecture analog-to-digital converter （ADC） fabricated on Analog Devices， Inc.’s iCMOS high voltage process. The device is configured through hardware or via a dedicated write-only serial configuration port for input range and operating mode. The AD7631 contains a high speed 18-bit sampling ADC， an internal conversion clock， an internal reference （and buffer）， error correction circuits， and both serial and parallel system interface ports. A falling edge on CNVST samples the fully differential analog inputs on IN+ and IN?。 The AD7631 features four different analog input ranges. Power is scaled linearly with throughput. Operation is specified from ?40°C to +85°C.