I was recently reading an article written about oscilloscope probing. And at one paragraph there is a comparison between active and passive probes as in the below quote:
"For high-frequency applications (greater than 600 MHz) that demand precision across a broad frequency range, active probes are the way to go. They cost more than passive probe and their input voltage is limited, but because of their significantly lower capacitive loading, they give you more accurate insight into fast signals."
What does "capacitive loading" means in this context? Why are passive scope probes more prone to it in high frequencies?
Best Answer
For a passive device the probe, the cable and the scope input have capacitance seen at the input: -
Here's a circuit of an active probe: -
It uses a JFET (or MOSFET in the case above) to buffer the input. Here's a typical comparison between the probes: -