Low value R "I/V" with the PCM1738...

AW · 19th June 2005, 08:32 PM

...type of DAC?

Older Iout DACs were ground referenced so it was easy - but these things sit the Iouts up at half rail - which makes life a tad difficult if you want to do it KISS style.

I can see how to do it differentially - by running the R between the + and - current outputs and taking a differential signal from across them - but without using an opamp (which I hate) or a transformer (which I also hate - but not as much as opamps) it's more complex than i wany.

And you can't take the R to gnd and have the DAC survive - don't ask me how I know...

Anyone made this work simply?

Allen

Jocko Homo · 19th June 2005, 08:45 PM

Somehow I don't think that they had KISS in mind when they designed it...............

I suppose that you could make a voltage reference, bias it up at Vcc/2......isolate it with a big resistor..............tie that to 2 smaller I/V resistors tied together...take the other end of them to the +/- outputs.

But I would go for active stage that didn't need an op-amp, because that is what I do best.

BTW.......I know that some DACs won't work if you don't use a load to ground. Don't ask how I found out by forgeting to hook up which wire and when................

Jocko

19th June 2005, 08:32 PM	#1
AW diyAudio Member Join Date: Jan 2004 Location: Europe	Low value R "I/V" with the PCM1738... ...type of DAC? Older Iout DACs were ground referenced so it was easy - but these things sit the Iouts up at half rail - which makes life a tad difficult if you want to do it KISS style. I can see how to do it differentially - by running the R between the + and - current outputs and taking a differential signal from across them - but without using an opamp (which I hate) or a transformer (which I also hate - but not as much as opamps) it's more complex than i wany. And you can't take the R to gnd and have the DAC survive - don't ask me how I know... Anyone made this work simply? Allen

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19th June 2005, 08:45 PM	#2
Jocko Homo Banned Join Date: Feb 2002 Location: As far from the NOSsers as possible	Somehow I don't think that they had KISS in mind when they designed it............... I suppose that you could make a voltage reference, bias it up at Vcc/2......isolate it with a big resistor..............tie that to 2 smaller I/V resistors tied together...take the other end of them to the +/- outputs. But I would go for active stage that didn't need an op-amp, because that is what I do best. BTW.......I know that some DACs won't work if you don't use a load to ground. Don't ask how I found out by forgeting to hook up which wire and when................ Jocko

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