[SI-LIST] Re: Passive Probe
- From: Doug Smith <doug@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 25 Feb 2011 23:02:17 -0800
Hi Orin,
The accurate bandwidth of such probes is for the most part about 50 MHz
no matter what the manufacturer says. Resonance and loading effects
above 50 MHz can easily affect circuit operation (input impedance just a
few Ohms!) and errors of 100% or more in amplitude are often seen. The
published data is taken in a way that is not applicable to how they must
be used to be practical.
They are great for audio circuits.
Doug
On 2/25/11 3:38 PM, Orin Laney wrote:
> It's actually a 9Mohm resistor that forms a 10:1 divider with the standard
> scope 1Mohm input resistance. There is also a small cap in parallel so that
> the time constant of the probe matches that of the scope input and frequency
> response is flat. These probes usually have a small trimcap that the user
> can adjust for flattest response. There's more that makes a good scope
> probe, but like Steve said you should troll the Tektronix site for the
> applicable app notes.
>
> Orin Laney
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of See Hour
> Sent: Friday, February 25, 2011 2:30 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Passive Probe
>
> Hello Gurus
> 10:1 Capacitive-input probes has a 10Mohm series resistance at probe tip.
> What is the purpose of the resistor?
> The answers that I have in my mind are:1) to be able to measure high DC
> voltage2) so that the input capacitive loading is small3) to minimize the
> loading that the cable capacitance would impose on the DUT
> Am I right about?
> RegardsYing
>
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