Best methods for I/V conversion?

[ezkcdude]

So, from what I understand there are at least three main ways to do I/V conversion at the DAC output stage:

1) (active) using op-amps and feedback

2) (passive) resistor

3) (passive) transformer

I'd like to hear what your preferences are (pros and cons) and why? Also, what are the DAC specifications that I need to take into account when making this decision?

[Uchi Deshi]

Comparation there is here.

[00940]

You forget active with discrete output stages and no feedback.

- The opamp solution is easy and gives good enough results if the opamps are good.

- The active path with no feedback gives very good results at a reasonable price (costs less than the best opamps for sure) but it's a bit more work to adjust the I/V stage.

- I never was really happy with passive and just a resistor. Anytime I tried it (single tda1545-tda1543), the simple discrete active I/V suggested by rbroer performed better.

- Transformers based I/V are too expensive for my taste, never tried them.

[ezkcdude]

Originally posted by 00940
You forget active with discrete output stages and no feedback.

-

I didn't forget, I'm just not that knowledgeable

Anyway, that sounds interesting. Do you know of any specific threads or web sites discussing this?

[wenye]

Agree with Ben.

Active I/V all way be the best in resonable cost.

Risistor can not get right performance.
Because of when output voltage from dac close to 0.6V, the internal protecting diode will become turn on and it will cause too more distortion products.

For risistor I/V, if you don't want to have any additional distortion with internal diode, then the output voltage from dac have to lower then 300mV. For a 20bit dac, it mean the lsb will be 0.286uV! It's too low.....

So, please go to the best way for I/V --- active I/V

[00940]

Originally posted by ezkcdude
I didn't forget, I'm just not that knowledgeable

Anyway, that sounds interesting. Do you know of any specific threads or web sites discussing this?

This is the most classical topic on the subject : Easy-to-build I/V stage

Rbroer made quite a few variations for the tda154* chips :

Simple I/V for TDA1541
"Super-Pair" I/V for TDA1543
Less simple I/V for TDA1541
Single rail, active I/V for TDA1543, TDA1545A
Simple ACTIVE I/V for TDA1543

For balanced output, there's of course the multiple variations on the D1 I/V stage, from Nelson Pass, a search should give you a lot.

Another way to do the I/V is to use some special chips, see Pedja's website. Never tried that myself : http://users.verat.net/~pedjarogic/a...a_dac_home.htm

[ezkcdude]

Thanks, 00940. That should keep me going for a while.

[ezkcdude]

I did a little research. Would something like OPA633 (operating open loop) in series with a resistor work?