AnsweredAssumed Answered

33120 arb waveform offset

Question asked by jackm on May 27, 2014
Latest reply on Jun 1, 2014 by jackm

Like • Show 0 Likes0
Comment • 2

I want to generate waveforms with small amplitude relative to the DC offset, e.g. a square wave going between 1.0 and 1.01V. The regular DC offset field is limited to twice the waveform amplitude. But the real problem is the way the 33120 scales output by the peak-to-peak range of the arbitrary waveform data. The output appears to be:

volts = amplitude * DN / (MaxDN - MinDN) + offset

For my example 1.0 to 1.01V, the best I can do is
     amplitude = 0.01
     offset = 0.02
     MaxDN = 2047
     MinDN = 2026

Then the actual output is 0.985 to 0.995 V. :(

I know about adding an external DC supply to offset the output, but is there some way to bypass the peak-to-peak range scaling? In the above example, if I create a waveform from 0.0 to 1.01V, using

     amplitude = 1.01
     offset = 0.505
     MaxDN = 2047 (output is 1.01V)
     MinDN = -2047 (output is 0V)
     and DN = 2006 for output = 1.00V

There's plenty of resolution - but adding the point at -2047 will cause a glitch in the output.

Thanks for any ideas.

No one else has this question

Outcomes

jackm May 31, 2014 7:01 PM

Actually, using an external DC offset still doesn't solve the problem - because I get an error from the unit if the amplitude is below 100mV.

I can't imagine why the thing has to scale by MaxDN - MinDN (instead of always scaling by 4094), it sure causes problems.

BTW: by "DN" I'm referring the the "DAC" values.

Actions

jackm @ jackm on Jun 1, 2014 10:52 AM

Maybe I'm just typing to myself here, but in case anyone is interested, I found the trick I needed.

The scaling of amplitude by the range of DAC values (max - min) in an arbitrary waveform is not performed when the waveform is defined, but only when the amplitude is set (by APPLy or VOLTage commands). For example:

- set waveform in range -2047 to +2047, set amplitude 1.0 -> output is -0.5V to +0.5V (output = DN/4094)
- change waveform to range 1000 to 2000 -> output is 0.244V to 0.488V (still output = DN/4094)
- set amplitude to 1.0 -> output is 1.0V to 2.0V (output = DN/1000)

So to get a desired offset or level when the scaling/amplitude/offset limits get in the way, setup a dummy waveform with suitable DN range, set the desired amplitude, THEN set the real waveform values.

Actions

2 Replies

jackm May 31, 2014 7:01 PM
Mark Correct
Correct Answer
Actually, using an external DC offset still doesn't solve the problem - because I get an error from the unit if the amplitude is below 100mV.

I can't imagine why the thing has to scale by MaxDN - MinDN (instead of always scaling by 4094), it sure causes problems.

BTW: by "DN" I'm referring the the "DAC" values.
Like • Show 0 Likes0
Actions
- jackm @ jackm on Jun 1, 2014 10:52 AM
  Mark Correct
  Correct Answer
  Maybe I'm just typing to myself here, but in case anyone is interested, I found the trick I needed.
  
  The scaling of amplitude by the range of DAC values (max - min) in an arbitrary waveform is not performed when the waveform is defined, but only when the amplitude is set (by APPLy or VOLTage commands). For example:
  
  - set waveform in range -2047 to +2047, set amplitude 1.0 -> output is -0.5V to +0.5V (output = DN/4094)
  - change waveform to range 1000 to 2000 -> output is 0.244V to 0.488V (still output = DN/4094)
  - set amplitude to 1.0 -> output is 1.0V to 2.0V (output = DN/1000)
  
  So to get a desired offset or level when the scaling/amplitude/offset limits get in the way, setup a dummy waveform with suitable DN range, set the desired amplitude, THEN set the real waveform values.
  Like • Show 0 Likes0
  Actions

33120 arb waveform offset

Outcomes

Related Content

Recommended Content