Signal distortion with AC coupling

[Kirkhaan]

Question to the experts:

I observe a signal distortion on my brand new ADP3450 when using AC coupling.

In attached screenshot I tried to capture this.

Both channel 2 and 4 have the same 1kHz, 500mVpp square wave feed.
In this example it is coming from an Agilent 33250A, but the observation is exactly the same when fed from the wave generator on the ADP3450.

Channel 1 and 2 show identical behavior. Exchanging the BNC cables does not make a difference.

When using one of the voltage probes that were included with the ADP3450, it also shows when the probe is set to 1:1.
When the probe is set to 1:10 attenuation (so 9MΩ impedance), it is not shown anymore, so then the square wave is flat on top and bottom and exactly matches the signal shape that we see with DC coupling.

What are we looking at here?
Is the 50Ω output of the signal generator somehow too much load for the ADP3450 inputs when using AC coupling???

 

Edited Saturday at 07:27 AM by Kirkhaan
Correcting typo

[attila]

Hi @Kirkhaan

This is the effect of AC coupling acting as a high-pass filter.

[Kirkhaan]

Aha, fair enough. I never observed that before with other bench-top scopes.
Probably because the models I worked with have bandwidth >400MHz.