Why there is amplitude drop after injected the pulse to a circuit?

I generate a pulse with 3.3 V amplitude. I set the load High Z and verified it with an Oscilloscope. But after I connected it to a circuit, its amplitude dropped to 2.0 V. I monitored the pulse with an Oscilloscope at the same location it was injected.

Carrie,<br> There may be a drop because of a voltage division from what your circuit is composed of, even if you measure at the same location it's injected to.<br> <img alt="" src="https://i.imgur.com/0teEra0.png"><br> How high of a frequency are you operating at?<br> <br> Best,<br> Iris Xu

Hi Iris,<br> <br> Thanks for your reply.<br> <br> The pulse is set at 100 KHz. The voltage dropped before I powered on the circuit. I measured that the circuit impedance is very high, OL. I felt confused that I have set the load High Z. How could it still affect the amplitude? I also tried to set the load to 50 Ohm. The same case when connected to the circuit.&#160;

Carrie,<br> Resistors are passive elements, so whether you had the circuit powered on in this case does not matter. The frequency you're operating at shouldn't introduce reflections just yet.<br> I would recommend watching <a href="https://www.tek.com/en/video/how-to/50-ohms-output-impedance-on-function-generators">this video</a>&#160;from Tek to see exactly what 50 Ohm vs High-Z means within the context of an AFG output, oscilloscope, and how you should expect it to affect your measurements when bringing in a circuit. It gives a better visual example in changes that occur than what I can provide here.<br> <br> -Iris

<p>Thanks Iris. I will do.</p>