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NI USB-6356 record problem

Hi there,

 

I tried to record a RF waveform ~800mV and 20kHz. I checked RF signal looked great with scope. However, I got very different result with NI USB-6356 Analog input. Can anyone give me some suggestions?

 

Thanks,

Wei

 

20211006_162130.jpg20211006_162152.jpg

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Please provide more information,

  • Exact circuit diagram of the connections
  • Attach the VI used to capture the data
  • DAQmx settings used for data capture
    • sampling rate, voltage range, NRSE or DIFF etc.,

 

I observe that you've enabled 50-ohm termination on the scope, have you implemented the 50-ohm termination for the DAQ?

-Santhosh
Semiconductor Validation & Production Test
Soliton Technologies
NI CLD, CTD
LabVIEW + TestStand + TestStand Semiconductor Module (2013 - 2020)
NI STS for Mixed signal and RF
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Hi Santhosh,

 

Thank you for your information!

 

I thought all the AI ports are 50-ohm. Would you please let me know why we need 50-ohm termination for DAQ? If I need to use ports 0~3, shall I terminate ports 4~7 with 50-ohm connector?

 

Regards,

Wei

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50-ohm termination is available only for high-speed or RF instrumentation, the DAQ you've is neither and hence required a 50-ohm termination at the input.

 

Typically all DAQ ADCs are high-impedance to measure small signals and not to load typical circuits. As mentioned in the specifications, the input impedance is very high.

santo_13_0-1633666301407.png

 

I would definitely recommend a 50-ohm resistor at the AIs or else your RF signal is driven into high impedance causing harmonics and double the voltages.

 

Just a 50-ohm connector such as SMA/SMB will not be sufficient, you definitely need a 50-ohm resistor to gnd at the front of AI.

-Santhosh
Semiconductor Validation & Production Test
Soliton Technologies
NI CLD, CTD
LabVIEW + TestStand + TestStand Semiconductor Module (2013 - 2020)
NI STS for Mixed signal and RF
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