The AD7731 is a complete analog front-end for process control
applications. The device has a proprietary programmable gain
front end that allows it to accept a range of input signal ranges,
including low level signals, directly from a transducer. The sigmadelta
architecture of the part consists of an analog modulator
and a low pass programmable digital filter, allowing adjustment
of filter cutoff, output rate and settling time.
The part features three buffered differential programmable gain
analog inputs (which can be configured as five pseudo-differential
inputs), as well as a differential reference input. The part operates
from a single +5 V supply and accepts seven unipolar analog
input ranges: 0 to +20 mV, +40 mV, +80 mV, +160 mV,
+320 mV, +640 mV and +1.28 V, and seven bipolar ranges:
±20 mV, ±40 mV, ±80 mV, ±160 mV, ±320 mV, ±640 mV and
±1.28 V. The peak-to-peak resolution achievable directly from
the part is 16 bits at an 800 Hz output rate. The part can switch
between channels with 1 ms settling time and maintain a performance
level of 13 bits of peak-to-peak resolution.
The serial interface on the part can be configured for three-wire
operation and is compatible with microcontrollers and digital
signal processors. The AD7731 contains self-calibration and
system calibration options and features an offset drift of less
than 5 nV/°C and a gain drift of less than 2 ppm/°C.
The part is available in a 24-lead plastic DIP, a 24-lead SOIC
and 24-lead TSSOP package.
