AD9712 general recommendations

Document created by analog-archivist Employee on Feb 23, 2016
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We want to update our application based on AD9712 . What we need is indicated
on page 7 of AD9712 datasheet. We checked AD9752 but we need to have > 3.5 Vout
, and the total settling  time to 35ns( to reach 0,1 % error ). We need to add
single ended or differential amplifiers. What about I-V amplifiers?


Could you share more detail about your application. Figure 5 in the AD9712B
datasheet shows one technique for converting the current output from a high
speed DAC into a voltage. It uses a current feedback amplifier to keep high
bandwidth because at the time the datasheet for the AD9712B was written current
feedback opamps were the only choice available when looking for bandwidths over
a few 10s of MHz.

Now voltage feedback amplifiers are available with bandwidths up to and beyond
300MHz; see the AD8057 for example and you don't have the common mode
restrictions of the AD9617 design.

I-V conversion of a highspeed DAC is a very general purpose operation. It would
be useful to know some more about the final application in order to offer the
most comprehensive range of solutions. For example, if the application is for
digital signal synthesis, you may be able to make use of our integrated DDS
chips such as the AD9830, AD9850, AD9852 and AD9853. On the AD9850, for
example, you can produce signals up to 100MHz, and program frequency, amplitude
and phase digitally.

If the application is for the transmit path of an RF system where guaranteed AC
performance is the most important criteria, the AD97XX series of TxDACs would
be a good starting point.

If settling time is the overriding concern, there are (at least two) points to
consider. The update rate of the system will be determined by the speed of the
digital logic in the DAC. The actual settling time will be primarily determined
by the choice of amplifier for I->V conversion. The input bias, input
capacitance, slew rate and bandwidth of the amplifier will all affect the
settling time.

For output settling time of 35ns and 12 bit resolution, the AD768, AD9762 and
AD9774 will meet the criteria. For the output amplifier, you need a bandwidth
of >30MHz,  slew rate to rise 5V in 35ns so 150V/us, low input bias current and
low input capacitance. AD825 or AD823 would be good starting points.

If you can provide more info we can refine these recommendations.