On Fri, 26 Apr 2019 16:36:38 -0700, you wrote:
As a result of my recent purchase of a Tek scope with 1 ghz. bandwidth, I have begun looking for probes. I have looked at the specs for a P6243 and a TPP 1000, both rated at 1 ghz bw. Both instruction manuals show a chart of impedance vs frequency. In either case the impedance decreases with frequency (makes sense because of capacitance) to a few hundred ohms at 1 ghz. Am I missing something here? Doesn't that load down the observed ckt in the DUT to the point where the probe (and attached scope) are essentially useless at their rated high end? Thanks in advance for taking the time.
I have found a similar problem, not with probes, but with circuits.
The higher the impedance, the more that the circuit capacitance limits
the bandwidth.
Most of the 200 Mhz or higher circuits look like a low impedance
driver, I've put a 10:1 50 ohm probe on a TTL circuit, and the probe
worked well enough (driving 500 ohms).
Naturally, an active probe has less capacitance and lower loading at
the expense of more limited voltage range and more fragile
electronics.
Harvey
Jack Reynolds
