differential output

[Agent K]

Hi,

Has anyone generated a differential signal (sine wave with 1Vpp) using NI PCIe-6521 hardware? I like to use signal to test a DAC for INL/DNL.  Sample code or pointers would greatly be appriciated.  Thanks.

[Dennis_Knutson]

The 6521 does not have any analog outputs. Have you looked at it and the specs?

[Agent K]

Hi Dennis,

Thanks for responing.  I checked and the device does have two 16 bit analog output.

NI PCIe-6251

16-Bit, 1.25 MS/s (Max), 1 MS/s (Scanning), 16 Analog Inputs

• National Instruments recommends the X Series PCIe-6351 for new applications
• Two 16-bit analog outputs (2.8 MS/s); 24 digital I/O; 32-bit counters
• Correlated Digital I/O (8 clocked lines, 10 MHz); analog and digital triggering

[Agent K]

Dennis,

My mistake, I transpose the digits. Apologies.

[Dennis_Knutson]

So what do you actually have? If you do have analog outputs, you just use the 'input terrmina configurationl' input of the DAQmx Configure Channel function. There is something similar in the DAQ Assistant. Look at the shipping examples (Help>Find Examples>Hardware Input and Output>DAQmx>Analog Generation).

[Henrik_Volkers]

If use both channels, one with the inverted signal you get a differential output with AGND (0V) midpoint.

If you need a free floating differential output use a transformer, a 5B module or use a FDA (fully differential amplifier)  for example described in this TI appnote page 19.

[Henrik_Volkers]

or see Fig. 61 here

[Agent K]

Henrik,  Dennis,

Thank you for the excellent suggestion. I will give it a try.