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From: rackland@csis.dit.csiro.au (Ross Ackland)
Newsgroups: sci.electronics
Subject: Analog front end for an A/D ~ 20
Message-ID: <1991Apr9.041010.22622@csis.dit.csiro.au>
Date: 9 Apr 91 04:10:10 GMT
Article-I.D.: csis.1991Apr9.041010.22622
Organization: CSIRO Division of Information Technology
Lines: 27

I am in the process of designing an A/D circuit to interface to a PC/AT
bus. I will use two Analog Devices AD7820's (1uSec conversion time) and
have finished the digital side of the design (address decoding etc) but
I am now struggling with the analogue side. The signals I am trying to 
digitise swing between +/- 2.5 volts and they are sampled at random intervals 
as close as 5 uSec apart (with the mean sampling interval about 50mSec).

The input to the A/D's requires non bipolar input (0 - Vref) and so if I 
select a Vref of 2.5 volts I need to scale the input and add a bit of
DC offset (preferably derived from the voltage reference).

Can anyone help me with this? Perhaps reccomend an Op-Amp with adequate
bandwidth, slew rate etc.. that would be suitable, or even some good
references or text books on Op Amp design, maybe even a circuit suggestion.


Thanks in advance
Ross Ackland

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