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It seems to me that voltage output DAC can do all the jobs of a current output DAC. When shall a current output DAC be used(superior than voltage output DAC)?

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I'm going to answer this for just those DACs that contain an R-2R network that converts a digital number to an analogue value. Here's a current output DAC of this type: -

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Interestingly, the R-2R network can be used a number of ways to get the same result. here's a different method but this time it uses a current to voltage converter made from an op-amp: -

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Here's another play on the same R-2R theme. This time a high impedance buffer amp is used: -

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So, you can either have an un-buffered current output DAC and choose to convert that output to a voltage OR you can have a DAC with the voltage buffer built in. In extreme situations you may decide that the internal voltage buffer isn't as good as you want and you might choose an un-buffered R-2R DAC and do the conversion yourself.

There are also those occasions when you might want to build a digitally controller multiplier - maybe you want to alter the amplitude of an analogue signal - if this is the application then an un-buffered 2-2R DAC is going to be the one you choose. These types of DACs are generally called multiplying DAC: -

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The above is a 2 quadrant one but you can make 4 quadrant types: -

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  • \$\begingroup\$ @richieqianle - was this answer suitable for you? \$\endgroup\$ – Andy aka Sep 9 '16 at 13:05
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For low enough speeds, for high enough noise, you are absolutely correct.

If you want to generate 100MHz signals (or even much slower), or DC voltages with single digits of nV/Hz noise on them, then current output is your only choice.

And yes, it's nice to use a fully integrated, voltage output, internal reference, multi-channel DAC when you can.

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Current output DACs are good for driving RF transformers. Here's an example from the popular AD9851 DDS chip's current-output DAC:

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At higher frequencies such as with the AD9956, the balanced current-out into a transformer/balun is standard.

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