AD7711

The AD7711 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 one differential analog input and one single ended analog input as well as a differential reference input. Normally, one of the input channels will be used as the main channel with the second channel used as an auxiliary input to periodically measure a second voltage. It can be operated from single supply (by tying the VSS pin to AGND) provided that the input signals on the analog inputs are more positive than30mV. By taking the VSS pin negative, the part can convert signals down to VREF on its inputs. The part provides two current sources that can be used to provide excitation in three- wire and four-wire RTD configurations. The AD7711 thus performs all signal conditioning and conversion for a single or dual channel system.

The AD7711 is ideal for use in smart, microcontroller based systems. Gain settings, signal polarity, input channel selectionand RTD current control can be configured in software using the bidirectional serial port. The AD7711 contains self- calibration, system calibration and background calibration options and also allows the user to read and write the on-chip calibration registers.

CMOS construction ensures low power dissipation, and a soft- ware programmable power-down mode reduces the standby power consumption to only 7 mW typical. The part is available in a 24-lead, 0.3 inch wide, plastic and hermetic dual-in-line package (DIP) as well as a 24-lead small outline (SOIC) package.