Hi,
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.
Regards,
Tom
Hi Tom,
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?
Zhuo Peng
Hi again Zhuo Peng,
We are working on that. As soon as we have an app note ready, we'll let you know.
Hi Tom
Thank you very much!
I am looking for your information.
Any progress on application note?
Hi Jason,
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.
-Mark
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?
Jason,
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 berarducci_mark@ti.com to start up a software agreement form.
Yes DAC9881. Linearity is pretty good, but will not match the -125dB THD level of DAC1280.
Mark
same problem for me, can we talk about that offline?
Tnx a lot in advance
Massi
You can E-mail me.