I have a basic understanding of the of coupling settings on an oscilloscope, but I need some help to understand what I am seeing on scope.
I have a signal generator, with an arbitrary function set, a 20 us pulse HIGH with 80 us LOW. Amplitude is set to 10 V, and the signal generator allows me to set between -511 to +511 points to shape the signal. I set the first point at +511 (for 20 us) and the remaining at 0 (for 80 us).
When I connect to the oscilloscope to measure the signal, depending on the coupling chosen I get different outputs.
- DC 1 MOhm, shows me the pulse approximately at 10 V peak.
- AC 1 MOhm, shows me a similar approximately 10 V peak, but shifted down -2 V.
- DC 50 Ohm, shows me approx. 5 V peak pulse
When I connect the output from the signal generator to my circuit, (I am using the signal to control a MOSFET,) if the DC coupling is ON on the scope, the voltage is not high enough to turn on my MOSFET, but if I us the DC 1 MOhm coupling then it works fine.
I would like to understand what is happening with the different coupling settings. Particularly why signal is approximately halved from the 1 MOhm to 50 Ohm. And why it effects my circuit in the way it does?
And any advice, in terms of coupling choice, when wanting to make measurements of signals and voltages across parts of a circuit, would also be appreciated?