Analog Devices AD7781 Manuals

ANALOG DEVICES UG-079 handbook

This user guide describes the evaluation board for the AD7781, which is a pin programmable, low power, 20-bit sigma-delta (Σ-Δ) ADC. The AD7781 is a complete analog front end for low frequency measurement applications such as bridge sensor systems. It contains one differential input and includes a low noise instrumentation amplifier. The output data rate can be programmed to 10 Hz or 16.7 Hz. The AD7781 also has an on-board clock, eliminating the need for an external clock. It employs a Σ-Δ conversion technique to realize up to 20 bits of no missing codes performance. The input signal is applied to an analog modulator. The modulator output is processed by an on-chip digital filter. The analog input channel of the AD7781 accepts analog input signals of ±V REF or ±V REF/128. With the update rate programmed to 10 Hz, the rms noise is 44 nV when the gain is 128. Simultaneous 50 Hz/60 Hz rejection is available at both output data rates. Full data on the AD7781 is available in the AD7781 data sheet available from Analog Devices, Inc., and should be consulted in conjunction with this user guide when using the evaluation board. The evaluation board interfaces to the USB port of an IBM- compatible PC. Software is available with the evaluation board that allows users to easily communicate with the AD7781. Note that the AD7781 evaluation board software should be installed before connecting the AD7781 evaluation board to the PC. Another component on the AD7781 evaluation board is the ADP3303 high precision, low power, 3.3 V output voltage regulator, which is used to power the USB/SPI interface.