Audio DAC as signal generator (Need DC output). - Page 2 - diyAudio
Go Back   Home > Forums > Source & Line > Digital Source

Digital Source Digital Players and Recorders: CD , SACD , Tape, Memory Card, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 5th December 2002, 08:27 PM   #11
haldor is offline haldor  United States
diyAudio Member
 
Join Date: Aug 2001
Location: Columbus, Ohio
Hi Janneman,

I have looked at National Instruments. Their DAC outputs are also 16 bits. I was hoping to get 20 bit resolution or better if possible.

Since we are measuring a very small signal I am concerned about the noise that any PC based analog output device is going to add. I think we are more likely to get better performance from an external box that is not powered by the PC's power supply.

Some further digging has turned up a "to Wave" function in Matlab. If this will do what we need then we could then play the wave file through a digital output of a sound card to the outboard DAC. Seems like it should work. Got some more digging to do.

Phil
  Reply With Quote
Old 5th December 2002, 08:29 PM   #12
haldor is offline haldor  United States
diyAudio Member
 
Join Date: Aug 2001
Location: Columbus, Ohio
Quote:
Originally posted by Pjotr
A program that convert .wav to .text and vice versa (and many other formats) is Goldwave. 16 bit only as far as I know. It is shareware: http://www.goldwave.com/
Thanks I will download that and see if does what I need.

Phil
  Reply With Quote
Old 5th December 2002, 08:32 PM   #13
diyAudio Member
 
Pjotr's Avatar
 
Join Date: Nov 2002
Location: Netherlands
Quote:
Originally posted by haldor
One displayed increment size in this particular product is 0.45 uV. We maintain an internal working resolution of 10 times that = 0.045 uV per minor increment.

Phil
That means you are pretty close to the noise levels of the semiconductor components. If you use any measurement card you need to limit bandwidth (lo-pass filter) and/or use averaging.
  Reply With Quote
Old 5th December 2002, 09:02 PM   #14
diyAudio Member
 
Pjotr's Avatar
 
Join Date: Nov 2002
Location: Netherlands
Hi Phil,

Attached is a picture of the noise performance of the M-Audio card at 24 bit resolution. It was a single shot record without averaging taken in loop-back with a small external cable. dB scale is referred to full scale. I did some extra filtering on the +12V and Ė12V of the PC.

One advantage of a soundcard is you can select sample rates as low as 8 kHz for longer measurements. Check the possibilities of a particular sound card for the sample rate before choosing one.

Attached Images
File Type: gif dist_2496_24bit_-80db_log_2.gif (22.0 KB, 207 views)
  Reply With Quote
Old 5th December 2002, 09:16 PM   #15
haldor is offline haldor  United States
diyAudio Member
 
Join Date: Aug 2001
Location: Columbus, Ohio
Hi Pjotr,

Can you see the noise performance below 20 Hz? I need a DC output capability.

Phil
  Reply With Quote
Old 5th December 2002, 09:29 PM   #16
diyAudio Member
 
Pjotr's Avatar
 
Join Date: Nov 2002
Location: Netherlands
Quote:
Originally posted by haldor
Hi Pjotr,

Can you see the noise performance below 20 Hz? I need a DC output capability.

Phil
Hi Phil,

Not directly because the used software does not display graphically below 10 Hz. I can look it up in the data file. That goes to the lowest frequency the FFT allows, in this case just below 1Hz. For that I have to do the measurement again. Btw donít look at the mV scale at the scope window. It is not calibrated. From the spectro gram you can conclude the noise is below 20 bit level. When doing averaging 100 times the noise level will drop 15 dB, which means the AD/DA converter has near 24 bit resolution.

Maybe I have time next weekend to do some extra measurements.

  Reply With Quote
Old 6th December 2002, 12:27 AM   #17
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Default Take 2 DAC's

this was discussed at either Analog Devices or Linear Tech -- if you are in a hurry, you can take 2 DAC's and sum the voltages. That is, if you have 2 10 bit DAC's use a VRef of 5.00 (or 4.096, or whatever, you get the point) and another with a smaller VRef. You get a lot of steps very conveniently. To get to "Zero", Bias the inverting input of an opamp with the value of the lowest bits. If you use a Maxim 5250 you have 4 10-bit serial DAC's with 2 references. Each DAC has its own op-amp. An ideal device for just this situation.

Here's where you will get fouled up -- you need very low noise references for this, you need very careful attention to layout, and you can't pinch pennies on the op-amps -- you'll probably use something like the LT1115, Make sure you use top and bottom ground planes, keep all your digital signals away, etc., etc.
  Reply With Quote
Old 6th December 2002, 02:29 AM   #18
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Default replying to my own post

i believe that the MAX5250 has the inverting input on each channel available. thus you can set two of the DAC's to the lowest bit and feed that output 1/1024 of VRef to the inverting input of the two other the channels, then sum the outputs with a high quality, low leakage, low noise opamp.
  Reply With Quote
Old 6th December 2002, 11:12 AM   #19
diyAudio Member
 
Join Date: Oct 2002
Location: Hamburg, Germany
Default PCM1704

Phil,

how about the Burr-Brown/TI chip PCM1704? You can get an evaluation board from TI, it has 24 bit resulution, and nearly all parameters are controllable. Seems to have DC out, or can easily modified.

Info:
http://focus.ti.com/docs/prod/produc...Number=PCM1704
http://focus.ti.com/docs/tool/toolfo...er=DEM-DAI1704

Here in europe the board should be available from RS-components.

-peter
  Reply With Quote
Old 6th December 2002, 11:24 AM   #20
haldor is offline haldor  United States
diyAudio Member
 
Join Date: Aug 2001
Location: Columbus, Ohio
Hi Peter,

I like the idea of using an evaluation board for the PCM1704. We don't have time to create and debug a DAC board, so I am not interested in rolling my own at this point. I think I will get both the outboard DAC I found earlier and a PCM1704 evaluation board. Hopefully we can do what we need with one or the other.

I will be working on this for the next week or so. If anyone has any other thoughts or suggestions, I am very interested in what you think.

Thanks to everyone for the help and suggestions.

Phil
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Why TAS3103 no audio signal output? KevinChen Digital Source 6 25th February 2011 01:32 PM
Wanted: one audio signal generator sdaudio2 Swap Meet 0 6th May 2007 01:04 PM
FS: BK Precision 3001 Handheld audio signal generator davidhs Swap Meet 3 6th May 2007 06:18 AM
Class Evolution-Modulating SMPS output to track audio signal vectorplane Power Supplies 42 13th January 2007 12:33 PM


New To Site? Need Help?

All times are GMT. The time now is 02:29 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2