AD7711A

The AD7711A is a complete analog front end for low frequency measurement applications. The device accepts low level signals directly from a transducer and outputs a serial digital word. It
employs a sigma-delta conversion technique to realize up to 24 bits of no missing codes performance. The input signal is applied to a proprietary programmable gain front end based
around an analog modulator. The modulator output is pro-cessed by an on-chip digital filter. The first notch of this digital filter can be programmed via the on-chip control register allow- ing adjustment of the filter cutoff and settling time.

The part features two differential analog inputs and a differen- tial reference input. Normally, one of the channels will be used as the main channel with the second channel used as an auxil-
iary input to periodically measure a second voltage. It can be operated from a single supply (by tying the VSS pin to AGND) provided that the input signals on the analog inputs are more
positive than 30 mV. By taking the VSS pin negative, the part can convert signals down to VREF on its inputs. The part also provides a 400 m A current source that can be used to provide
excitation for RTD transducers. The AD7711A thus performs all signal conditioning and conversion for a single or dual chan-nel system.

The AD7711A is ideal for use in smart, microcontroller-based systems. Input channel selection, gain settings and signal polar-ity can be configured in software using the bidirectional serial
port. The AD7711A contains self-calibration, system calibration and background calibration options and also allows the user to read and write the on-chip calibration registers.