TI E2E Community
Precision Data Converters
Precision Data Converters Forum
DAC1280's external bitstream
I have some questions about DAC1280 for your help.As the datasheet(Page 1) said,an external 1s density digital bitstream is needed to driven the DAC1280.
How does the bitstream be builded?
What requirement should the bitstream be filled?
Is there any other devices available to make the bitstream?
Thank you！Best wishes！
Hi Zhuo Peng,
To understand the basic principle behind the bit stream, take a look at section 3 of this application note. The pattern you want to send to the DAC1280 would generally be driven from a bit stream modulator in an FPGA or microcontroller.
It's very exciting to receive you reply.Thank you very much.Now I am trying to make a sine waveform generator by a sigmal-delta DAC.I have to make the bitstream in FPGA.
But I still is puzzled about how to create a bit stream modulator in FPGA.Could you please show me some application notes or other more details about it?
Hi again Zhuo Peng,
We are working on that. As soon as we have an app note ready, we'll let you know.
Thank you very much!
I am looking for your information.
Any progress on application note?
Sorry for the delay here - can I ask you what sort of application you want to use the DAC1280 in? We've run into some roadblocks in trying to provide the bit-stream files for the DAC1280 due to a piece of proprietary code. I'm not going to be able to provide you with details on how to create the bit stream yourself without some NDA agreement in place. What I can do, is if you tell me the frequencies and amplitudes of the waveforms you'd like to create, I can have a bit stream file prepared for you.
Thanks for the information. We plan to use DAC1280 in broadband seismic devices for testing and calibrating. We need DAC to send out a highly accurate sine/square wave current less than 5mA to mechanical part of the system. The problem is we need waveform frequency from 0.01Hz to 1000Hz. It is almost impossible to prepare all bit stream before implementation. Are there any way to let microcontrollers dynamically generate the bit stream internally? If it is impossible, what kind of DAC you will recommend to do the job?We need a least 16 bits resolution on DAC.
It's a little difficult for most microcontrollers to generate the bitstream directly. The generetor routine needs 5 mulitple and 4 add operations with 28 bit wide registers all computed within 4uS.
A microocntroler would need hardware math unit to handle the math in this short time. Something like an ARM based micro with math engine may work, but most other micro will not keep up.
I have MATLAB code if you would like to go this route.
The other approach is using our 18bit muliplying DAC driven by a micro based look up table.
Let us know how we can help further.
We can use microcontroller to create the bit stream look up table when waveform is requested. Then we can send it out in traditional way. In our application, we can afford some delay from receiving request to real waveform sending out. We just can not limit the output waveform to some preset ones.
Could you please send me the MATLAB code? That will be very helpful. Do you need my email address?
For 18bit DAC, you mean DAC9881?
Yes, having the micro compute the bit pattern for playback at alter time greaty relieves the MIPS requirment.
Let's take the corrspondance off-line at this point. Please email me at firstname.lastname@example.org to start up a software agreement form.
Yes DAC9881. Linearity is pretty good, but will not match the -125dB THD level of DAC1280.
same problem for me, can we talk about that offline?
Tnx a lot in advance
You can E-mail me.
We are going to use DAC1280 output an anolog signal (31.25Hz) to the ADS1282 for the testing purpose.
However we are not clear that how to create a bitstream TDATA for DAC1280 by miro-processor, and the format of the bitstream, such as number of bits per sample, output amplitude (as sample Value), For inputing bitstream, is continuous or each sample by SYNC?
I didn't use the new ADS1280. But I did generate the bitstream using FPGA to make a 31.25Hz sine wave.
You can read some books about delta-simga DAC to find your resolvent.
Dear Zhuo Peng,
Thanks a lot for you reply.
Could you advise me the information about how to generate the bitstream?
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with respect to these materials. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.