Gibbs phenomenon issue in square wave from labview builtin function generator

[ritch_by_nature]

I have a server and client, I am sending commands to the server from my client to generate different waveform. but the display of my square wave and sawtooth waveform in the client has pikes and alot of harmonics to it. When I compare it with the display of the same waveform in my server, the square wave and sawtooth wave looks fine. Picture will show a comparison of both.

please help, i did some research and I am thinking it might be gibbs phenomenon happening and im not sure how to solve that.

[Bob_Schor]

I doubt it.  It looks much more like ringing, possibly due to over-compensating for cable capacitance.  Can you provide more details on your setup?  I gather the Server is generating the waveforms (how?  D/A?  What output rate?) and transmitting the data to the Client (again, how?  Digitally via TCP/IP?  Some other way?).  How did you get those images?  

[Bob_Schor]

Oops, I hit "Reply" when I meant to hit something else -- more questions coming ...  Are the images from a fast scope, or from a LabVIEW chart?

Bob Schor

[ritch_by_nature]

Yes the images from labview chart. Every thing is on my desk. Cdaq chassis has NI9239 for acquisition and NI9263. I'm using my laptop for both server and client running as local host.

[Bob_Schor]

How is the D/A converter wired to the A/D?  Are you using coax and the BNC connectors, or the screw terminals?  What sampling rates are you using?  Is there a load in the circuit anywhere?  Have you looked with an oscilloscope at any of the signals?

BS

[ritch_by_nature]

Im using wires straight from the NI 9263 to the 9239

[ritch_by_nature]

There's no circuits in between the two. I generate the data and I acquire it. All the cards are in the same chassis. My sampling rate is 1000Hz. I tried a scope before and I see the same thing my client was seeing in the square wave

[Bob_Schor]

Before I venture a guess at the genesis of your problem, I need to say that I am not an engineer (I'm a neurobiologist).  From your previous replies, it sounds like you have two (presumably unshielded, untwisted) wires connected the output from the D/A converter directly to the input of the A/D converter.

I think the problem is that there is no load.  If I am correct, connecting a resistor (I'd guess 1 MegOhm would be OK) across the D/A output would instantly fix your problem.

Here's my thinking.  A D/A converter is supposed to put a defined Voltage across a load, without knowing what the load will be.  So if you ask for 10 V and give it a 10Ohm load, it needs to pump out 1 amp, while if it is a MegOhm, it needs to output 10 microamps,  An A/D converter, on the other hand, should have a very high input impedance so that it draws almost no current from the circuit being measured, leaving all of the current to flow through the load across which it is making the measurement.

In your case, there is no defined load.  The D/A is trying to pump current into a circuit that is trying to have an infinite input impedance, and the A/D circuit is trying to read a voltage across the D/A circuit which is trying to have as close to zero output impedance (so all the voltage drop goes across the load) as possible.  Can you say "Impedance Mismatch"?  [My daughter, at the age of about 30 months, ducked her head under the water in the tub, spoke (and heard her voice "sounding funny"), and said "Look, Mommy, Impendance Mismatch!"].  [Spoiler Alert -- she'd heard the term from me ...].

Let us know if this fixes the problem.

Bob Schor

[mikeporter]

Hmmm... I thought the "Gibbs Phenomenon" was the physical sensation of having the back of your head slapped after saying something dumb.

Mike...

[Bob_Schor]

Ha, ha, ha -- old man Fourier would be rit dans sa tombe (as they say in French).

BS