Problems with fully bandwidth on DAC and ADC

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EMsoft
Posts: 1
Joined: Wed Oct 11, 2017 12:20 pm

Problems with fully bandwidth on DAC and ADC

Post by EMsoft » Wed Oct 11, 2017 12:57 pm

Hi, I work with a red pitaya 125-14 Starter kit. I like using just the DAC and ADC part of item. I checked this parts by oscilloscope with up to 20 GSps (for max. 1GHz bandwidth) and a signal generator with 500MSps (for max 160MHz bandwidth). I use the App “Osciloscope & Signal Generator” on red pitaya.

My setup for testing DAC is connection OUT1 or OUT2 to the real oscilloscope.
For testing ADC is connection IN1 and IN2 to real signal generator, real oscilloscope and 50 ohms impendence terminator.

Result of testing DAC is well until 2MHz. I’ve +3dB (more) amplitude at 9.2MHz than I should have. This is to less bandwidth. Result of testing ADC is the same. I’ve a -3dB (less) amplitude at 33 MHz than I should have. This is ok but it should be at bandwidth until 50 MHz.
You have no difference between factory calibration and calibration of you own.

Someone has an idea for fixing the problem?
thx
Michael
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amike88
Posts: 29
Joined: Tue Mar 29, 2016 7:41 pm

Re: Problems with fully bandwidth on DAC and ADC

Post by amike88 » Mon Oct 16, 2017 1:13 pm

Hi,

have you made sure that nothing is interfering with your measurements?
According to these measurements bandwidth should be 50 MHz.

gmb
Posts: 4
Joined: Sat Mar 18, 2017 11:05 pm

Re: Problems with fully bandwidth on DAC and ADC

Post by gmb » Thu Oct 19, 2017 9:50 pm

You did not use 50 Ohm termination. There ist some matching at the output that causes a big swing with its maximum at 23 MHz. Take a look at my measurements. Use proper 50 Ohm termination and the frequency response is reasonably flat.
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