The AD74521 is a 12-bit， high speed， low power， successive approximation （SAR） analog-to-digital converter that features a fully differential analog input. This part operates from a single 3 V or 5 V power supply and features throughput rates up to 555 kSPS. The part contains a low noise， wide bandwidth， differential track-and-hold amplifier （T/H） that can handle input frequencies up to 3.5 MHz. The reference voltage is applied externally to the VREF pin and can be varied from 100 mV to 3.5 V depending on the power supply and what suits the application. The value of the reference voltage determines the common-mode voltage range of the part. With this truly differential input structure and variable reference input， the user can select a variety of input ranges and bias points. The conversion process and data acquisition are controlled using CS and the serial clock， allowing the device to interface with microprocessors or DSPs. The input signals are sampled on the falling edge of CS， and the conversion is also initiated at this point.