DAC output level over frequency

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ctrofin
Posts: 1
Joined: Sat Jan 13, 2018 2:41 am

DAC output level over frequency

Post by ctrofin » Sat Jan 13, 2018 3:01 am

When running the 'Oscilloscope & Generator' app, I noticed that the DAC'c output amplitude varies with frequency with a level exceeding twice the set amplitude somewhere in the middle of maximum bandwidth.

So, at 10KHz and a level set to 0.5V it outputs 0.5V/10KHz, changing just the frequency to 20MHz, will output a voltage level of 1.6V. Going to 40MHz will output ~0.5V/40MHz. This is on 'Low Voltage' jumper setting.

Generating a frequency sweep from 1 to 40MHz using the SCPI API, shows that there is a amplitude hump in the middle of the bandwidth, which saturates the ADC if DAC-to-ADC loopback is used.

This is a brand new board. Is there a calibration/setting I should do to correct this or should I suspect something being wrong with the board?

The output level/frequency was measured on a Tektronix scope.

Thank you,
Chris

GeoffAU
Posts: 1
Joined: Wed Feb 08, 2017 4:20 am

Re: DAC output level over frequency

Post by GeoffAU » Wed May 23, 2018 1:12 am

The DAC has output filtering in it that assumes a 50 ohm connection. If you don't terminate it with 50 ohms you will end up with peaking as you've found.

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