High output resistance in a current steering DAC

[Yarrow]

Hi

I was wondering if anyone knows if it is normal to have a "high" output resistance in the kOhm range on the DAC output? I read a lot of papers state that the output resistance should be in the 25-100Ohm range. Is this because of speed or do heavier loads lead to other problems?

tnx in advance

 

[erikl]

Current steering DAC

A current steering DAC in the first instance has - as its name tells us - a current output, meaning a "high" output resistance. For a conversion into an output voltage it needs an appropriate resistor, and - for low output resistance - a buffer.

 

[Yarrow]

Re: Current steering DAC

Tnx

I see now that I formulated my question wrong.

What I meant to ask was if it is normal to have a "high" output RESISTOR in the kOhm range for converting the output current into an output voltage?

 

[dick_freebird]

Current steering DAC

More common to use an op amp to make a virtual ground,
and the feedback resistor sets the scale. The only current
steering DAC I ever worked on, had this resistor on chip and
trimmed like the rest.

Using a high value resistor is a way to get a voltage output on
the cheap. But if the output voltage deflection is anything
significant (like volts) it's probably causing some common
mode voltage related linearity errors. You'd have to look into
the details to see what output voltage range, current linearity
is guaranteed over.

 

[Yarrow]

Re: Current steering DAC

Thanx alot. It was helpful.