How to configure the dac to interpolating mode?

[sidda]

Hi Jerry,

I am Siddu Working in Jisnu communications ltd India. I am using the IFRIO 5640R. By using this I completed the AM and FM Demodulation up to 2MHz baseband signal. Now my problem was I want to give this demodulated data as a output without any upconversion. This is possible only when the dac is configured in interpolating mode. I read the DAC (AD9857) datasheet, in that he explained clearly. The DAC has 3 modes of operation. The 5640r examples are having only two modes i.e singletone mode and quadrature mode. What about the interpolating mode? Is it possible with IFRIO? Because my project was stucked at this point. I need to give the demodulated data as an output.  Please help me in this issue.

Siddu

[philippe_w]

Siddu,

We have not done testing with the Interpolating Mode, but if you are familiar with the DAC datasheet, you should be able to try it fairly easily.

If you look at the library of VI's we have provided, you will see the 'ni5640R DAC Configure for Quadrature Mode.vi' and 'ni5640R DAC Configure for Single-Tone Mode.vi'. If you make a copy of one of these (the Single-Tone is the simplest), name it ni5640R DAC Configure for Interpolating Mode.vi', and add it to the .lvlib in your project, you should be able to change it to configure the DAC for this mode.

Inside these VI's, there are several clusters of settings that are passed to DAC Program. The 'Operation' cluster has a 'Mode' field that can be set to 'Interpolating'. You may need to compare the other settings to the Datasheet to configure the DAC for your needs. You can also drill down into DAC Program and see exactly how the DAC registers are being set.

Let me know if this works for you.

~Philippe

[JerryAL]

Hi

First two points..

1. National Instruments (NI) doesn’t ship any API or examples to configure the DAC in interpolation mode. NI does not test this feature’s functionality.  This feature should work assuming the other features are working correctly.  But we haven’t done an in-depth analysis to determine if there are any cases where a component can fail but leave the supported features still available and working correctly.

2. The AO channels are AC coupled.  In interpolation DAC mode, components of generated waveforms below ~250 KHz may not be generated as expected.

 However, it should be possible to implement the interpolating DAC mode. First of all, I would advise you to read the DAC datasheet to learn how this mode is supposed to work. Then, my recommendation would be to open the VI called "ni5640R DAC Configure for Quadrature Mode.vi" and save it with a different name, like "ni5640R DAC Configure for Interpolation Mode.vi".

Inside these VI's, there are several clusters of settings that are passed to DAC Program. The 'Operation' cluster has a 'Mode' field that can be set to 'Interpolating'. You may need to compare the other settings to the Datasheet to configure the DAC for your needs. You can also drill down into DAC Program and see exactly how the DAC registers are being set.

Open the block diagram, and change the cluster from "Quadrature Modulation" to "Interpolating DAC". (See screenshots)

In interpolating DAC mode, the Transmit/Center Frequency doesn't mean anything, because the board is not upconverting to any frequency, it's just resampling the waveform you write to it. For the same reason, complex IQ waveforms are not used in interpolating DAC mode, but real waveforms.  As shown in the following image, create a waveform based upon the sample rate that is available for a given interpolation rate.  Due to the method that the NI 5640R transfers data to the DAC, the waveform must be decimated, converted to I16, and then combined to U32.  Each U32 data type will contain sample(X) and sample(X+1).  (Note: The NI 5640R uses the lower 14 bits of the I16 data type to transfer data to the DAC.)

Attached is an example converted from the ni5640R Analog Input and Output example that ships with the ni5640R software showing the steps used to implement the interpolating DAC mode.  It is created using LabVIEW 8.2.1.

Jerry

Message Edited by Jerry_L on 02-22-2008 05:08 PM

[JerryAL]

Adding example:

[sidda]

Hi Jerry,

Thanks a lot for giving the reply. I tested this code and working fine. But I have a small problem with Host to Fpga FIFO.

In this code, the Host to Fpga fifo was before the while loop. I want to put this fifo in side the while loop. When I am placing this fifo inside the while loop it is giving error(The transfer did not complete within timeout period error code was 50400). On this I have done so many experiments but I am not able to do this. Please help me in this issue. I am awaiting for your response.

Siddu 

[JerryAL]

Hi Siddu

What is your goal for putting the DMA write into the loop?

Do you want to continually generate new data?  Or just periodically when programmatically triggered?

Jerry

[sidda]

Hi Jerry,

I have the demodulated waveform data. I want to write that waveform data samples on to the DAC . For this purpose I want to put that DMA FIFO in side the whileloop. If I changed my input frequency i.e baseband frequency the output was also appear respective to the input. Please help me inthis issue.

Siddu

[JerryAL]

Hi Siddu

Sorry, I’m still not clear on what you are trying to do.  At least in terms of putting the writing waveform samples inside the while loop.  There are two reasons basic reasons for doing this.  The first is that you want to continually generate new waveform samples from the DAC, so that you are continually writing new data each iteration of the loop.  In this case, the program and hardware must get data to the module at a rate that is greater than the DAC sample rate, or you underflow, starve the DAC for new data.  The second reason is to write new data every so often. In this case, the waveform written to the FPGA will be looped on until the next time new data is written down to the FPGA.

I’m also not clear on the meaning of this line:
“If I changed my input frequency i.e. baseband frequency the output was also appear respective to the input.”

Jerry

[sidda]

Hi Jerry

I want to continually generate new data.

Siddu

[sree_405]

Hi Siddu,
i have some problem to generate modulated wave.plz help me
see my problem in this URL:
http://forums.ni.com/ni/board/message?board.id=ifrio&thread.id=647

Thanking you so much