ISingle ended output

[gnhj]

Hello,

I am using a PXIe-5450. Is there any way to select the output as single ended instead of differential.

The problem is that the output signal level is too low (300 mV pp), whereas it is specified on the datasheet that the maximum output is 1 Vpp.

Thanks

[jaced]

Hi gnhj,

The PXIe-5450 is a differential only device. That being said the voltage level you mentioned is below the maximum output for a differential signal. How are you configuring the device in software? To achieve Maximum voltage output you should load a Full Scale waveform to on board memory,meaning your data is normalized between -1 and 1. Setting the gain to .5 will provide a .5Vp or 1Vpp waveform at the output. Also, how are you measuring this voltage? The device must be measured differentially in order for a correct reading. The load impedance should also be configured to reflect the actual load applied. I hope this helps let us know if you have any further questionsor anything is unclear. The shipping examples are a great place to start. Start>>AllPrograms >>National Instruments>>NI-Fgen>>Examples. 

Message Edited by jaced on 03-04-2009 10:43 AM

[gnhj]

Hi jaced,

thanks for your reply.

I am using already one of the Labview examples provided by NI. The test signal I use is a standard sine wave normalized between -1 a1.

I actually also have several PXI-5422s and using the same example I can set the ouput voltage correctly according to the gain option in the software.

Just to clarify, I am using the 5450 in a "single-ended" fashion, so I am just taking the output from the Ch. 0 + output and measuring it with a normal oscilloscope.

So my question would be, is this output voltage that I am seeing correct?

If so is there any way to get something more out of the card if I use it "single-ended"?

Thanks 

[jaced]

Hi,

Ok now the issue is more clear. What you are seeing is expectedbehavior, this is due to the load being unbalanced, A work around for thiswould be to terminate the negative terminal with a matched load (i.e. If yourscope is set to 50 ohms use a 50 ohm terminator). This should balance theoutputs and increase the output voltage. The output voltage will never be aboveabout half of the differential voltage and the specifications do not hold forsingle ended operation, but terminating is an option. Depending on theapplication the use of a Balun may also be an option to consider.