DAC8811 eval board limited signal frequency

Hello Lars,

Unfortunately there are a couple of limiters.

1. The MMB0 internally limits the update rate to 1MSPS because the on-board DSP cannot generate a signal faster than that.
2. The XML file that corresponds to the DAC8811 further limits the update rate to 200kSPS.
   1. However this can be fixed by editing the DAC8811.xml

I went ahead and edited the file for you. You have to:

1. Copy the attached file into the DXP devices directory
   1. (Typically C:\Users\Public\Documents\DXP\Devices).
2. Relaunch DXP
3. Instead of using the DAC8811 profile, use the DAC8811_NR.
4. Now you should be able to have a max 1MSPS.

Having fixed that issue. I am concerned that the DAC stopped working. I would expect the update rate to be capped at 200kHz, but not for the DAC to stop working. Please let me know if this continues so we can investigate a little deeper.

I do have one question: By "stimulus frequency" you mean the frequency of the generated sinusoidal correct?

Running a 100kHz sine wave with a 1MSPS will give you about 10 points per cycle. It will not look very clean, but you should be able to see the general shape in your oscilloscope.

How can i access the attached file? I do not see any.

<?xml version="1.0" encoding="utf-8"?>
<device>
  <name>DAC8811_NR</name>
  <revision>1.0.0</revision>
  <date>21Aug2012</date>
  <devicesettings>
    <instructionwidth>16</instructionwidth>
    <format>sbinary</format>
    <dataword>DDDDDDDDDDDDDDDD</dataword>
    <commanddefault>0</commanddefault>
    <commandlatch>0</commandlatch>
    <maxupdaterate>1000000</maxupdaterate>
    <channels>1</channels>
    <interface>
      <type>spi</type>
      <polarity>0</polarity>
      <phase>0</phase>
      <maxsclk>50000000</maxsclk>
      <framebits>16</framebits>
    </interface>
    <latchpin>
      <feature>0</feature>
      <pulsepol>0</pulsepol>
    </latchpin>
    <FSplus>-2.5</FSplus>
    <FSminus>0</FSminus>
  </devicesettings>
</device>

I apologize. I forgot to attach the file. Here it is now. You should be able to click on the link above.

no change, there is no output generating a signal (e.g. sine) with a frequency > 100 KHz.

Lars,

Can you observe a waveform at 50kHz or 80kHz?

Maybe you can share an oscilloscope capture of what you are observing as well as a screen capture of your DXP setup.

I took some plots using the DAC8811EVM for your reference.

Even though at higher frequencies the sinusoidal shape is distorted, you should still be able to see a waveform.

Channel 2 - /CS

Channel 4 - Vout

100kHz Sine Wave

200kHz Sine Wave

400kHz Sine Wave (The Oscilloscope had a hard time reading the correct frequency)

Due to whatever reasons now i can see something. sometimes i have to restart DXP to get anything out of the evm-board. anyway, thanks for your support.

The MMB0 interface can very sensitive to spikes in the circuit, such as switching jumpers or touching a ground connection with your hands. This may cause the board to lose the connection without DXP being aware. This may be the reason for you having to restart DXP.

I'm glad that its working for you now. If you run into any other issues let me know and I will take a look at it.