The AD7903 is a dual 16-bit， successive approximation， analogto-digital converter （ADC） that operates from a single power supply， VDDx， per ADC. It contains two low power， high speed， 16-bit sampling ADCs and a versatile serial port interface （SPI）。 On the CNVx rising edge， the AD7903 samples the voltage difference between the INx+ and INx? pins. The voltages on these pins usually swing in opposite phases between 0 V and VREF. The externally applied reference voltage of the REFx pins （VREF） can be set independently from the supply voltage pins， VDDx. The power of the device scales linearly with throughput. Using the SDIx inputs， the SPI-compatible serial interface can also daisy-chain multiple ADCs on a single 3-wire bus and provide an optional busy indicator. It is compatible with 1.8 V， 2.5 V， 3 V， or 5 V logic， using the separate VIOx supplies. The AD7903 is available in a 20-lead QSOP package with operation specified from ?40°C to +125°C.