The AD7705/AD7706 are complete analog front ends for low
frequency measurement applications. These two-/three-channel
devices can accept low level input signals directly from a transducer
and produce a serial digital output. They employ a sigmadelta
conversion technique to realize up to 16 bits of no missing
codes performance. The selected input signal is applied to a
proprietary programmable gain front end based around an analog
modulator. The modulator output is processed by an onchip
digital filter. The first notch of this digital filter can be
programmed via an on-chip control register allowing adjustment
of the filter cutoff and output update rate.
The AD7705/AD7706 operate from a single 2.7 V to 3.3 V or
4.75 V to 5.25 V supply. The AD7705 features two fully differential
analog input channels while the AD7706 features three
pseudo differential input channels. Both devices feature a differential
reference input. Input signal ranges of 0 mV to +20ê mV
through 0 V to +2.5ê V can be incorporated on both devices when
operating with a VDD of 5 V and a reference of 2.5 V. They can
also handle bipolar input signal ranges of ±20ê mV through ±2.5ê V,
which are referenced to the AIN(–) inputs on the AD7705 and to
the COMMON input on the AD7706. The AD7705/AD7706,
with 3 V supply and a 1.225 V reference, can handle unipolar
input signal ranges of 0 mV to +10ê mV through 0 V to +1.225ê V.
Its bipolar input signal ranges are ±10ê mV through ±1.225ê V.
The AD7705/AD7706 thus perform all signal conditioning and
conversion for a two- or three-channel system.