The AD7938/AD7939 are 12-bit and 10-bit， high speed， low power， successive approximation （SAR） analog-to-digital converters （ADCs）。 The parts operate from a single 2.7 V to 5.25 V power supply and feature throughput rates up to 1.5 MSPS. The parts contain a low noise， wide bandwidth， differential track-and-hold amplifier that can handle input frequencies up to 50 MHz. The AD7938/AD7939 feature eight analog input channels with a channel sequencer that allows a preprogrammed selection of channels to be converted sequentially. These parts can operate with either single-ended， fully differential， or pseudo differential analog inputs. The conversion process and data acquisition are controlled using standard control inputs that allow easy interfacing with microprocessors and DSPs. The input signal is sampled on the falling edge of CONVST and the conversion is also initiated at this point. The AD7938/AD7939 have an accurate on-chip 2.5 V reference that can be used as the reference source for the analog-to-digital conversion. Alternatively， this pin can be overdriven to provide an external reference.