Part recommendation

Document created by analog-archivist Employee on Feb 23, 2016
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I spoke to you briefly this morning regarding selecting an ADC for a new
instrument we are developing, I have looked on the AD website but there is no
parameter search that I could find for ADC's.The main parameters I require are
as follows :-1. Resolution >= 14 bits, parallel output
2. Conversion time < 2us.
3. DNL < 1 lsb
4. Snap shot operation (Not continuos sampling)
Optional features
1. Internal reference
2. Internal sample & hold


Up until fairly recently, the only way to get 14 bit resolution with conversion
time of >2us was to use a sigma delta architecture or to use a very high speed
pipeline architecture ADC with throughput rates in the 10MHz region (See AD7721
and AD9260 for examples of sigma delta  parts and AD9240, AD9243 for examples
of high speed pipeline devices). It is quite possible to get pipeline ADCs with
throughput rates up to the high 10s of MHz range at 12 resolution ( see the
AD9224 and AD9226 for example) but to get the conversion time, i.e. the time
between applying the signal  and obtaining a result as opposed the time between
successive conversions, down to below 2us for 14bit resolution is pretty

The AD7863 which Irfan suggests comes close but the conversion time is nearer 5
or 6 us and as you say it's dual where only a single is required. From the
sound of your spec, what you really want is a Successive Approximation Register
(SAR) ADC where you can hit the Convert Start signal asynchronously and get a
result back within the specified time.  Current Successive Approximation
devices are just not fast enough to meet this spec.  In fact the closest you
can get with currently release parts from ADI is the AD7851, 14 bit single
converter with a conversion time of 2.78us

At Analog Devices we are working on improving the speed of SAR ADCs with a new
high speed low power SAR core and we have had significant success in achieving
high speed operation (>1us) at 10 and 12bit resolution. It's much harder to
maintain this speed up to 14 bit resolution but one of our new (soon to be
released) ADC pushes the envelope out slightly and achieves the 2us conversion
time (quite a feat for a SAR converter). The product is the AD7899 which is as
yet unreleased. It is scheduled for general release at the end of July and
Samples will be available from Impact at that time.