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The AD7705/AD7706 are complete analog front ends for lowfrequency measurement applicaTIons. These two-/three-channeldevices can accept low level input signals directly from a transducerand produce a serial digital output. They employ a sigmadeltaconversion technique to realize up to 16 bits of no missingcodes performance. The selected input signal is applied to aproprietary programmable gain front end based around an analogmodulator. The modulator output is processed by an onchipdigital filter. The first notch of this digital filter can beprogrammed via an on-chip control register allowing adjustmentof the filter cutoff and output update rate.The AD7705/AD7706 operate from a single 2.7 V to 3.3 V or4.75 V to 5.25 V supply. The AD7705 features two fully differenTIalanalog input channels while the AD7706 features threepseudo differenTIal input channels. Both devices feature a differenTIalreference input. Input signal ranges of 0 mV to +20Ê mVthrough 0 V to +2.5Ê V can be incorporated on both devices whenoperating with a VDD of 5 V and a reference of 2.5 V. They canalso handle bipolar input signal ranges of ±20Ê mV through ±2.5Ê V,which are referenced to the AIN(–) inputs on the AD7705 and tothe COMMON input on the AD7706. The AD7705/AD7706,with 3 V supply and a 1.225 V reference, can handle unipolarinput 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 andconversion for a two- or three-channel system.
