[SI-LIST] Re: Single tip probe accuracy

Hi Shahar,

If the probe input impedance is high enough, the return path back to 
the circuit for the probe is just capacitance from the probe to the 
board or chip. While the waveform might look good, there is a catch. 
The probe will be displaying the signal node relative to an "average" 
ground of the board or chip. Gates see the signal relative to their 
local ground, and so may see something different that what the probe 
displays on the scope.

The waveform will also show any transient in the room since the signal 
return for the probe is not compact. If you are looking for a glitch, 
you will likely see every glitch in the room as well as your circuit.

Doug

Eytan, Shahar wrote:

> Hello,
>  
> 
> I'm looking for high frequency probes to use on Pico-probe station,
> measuring on package or die. I'm interested in both timing and signal
> quality (accurate signal voltage and shape).
> 
> I ran into very low active probes that use only single tip, no ground is
> required.
> 
> I was wondering how accurate are those probes (to measure voltage
> effects), considering the fact they have no ground tip? What is the
> theory behind those probes operation?
> 
>  
> 
> Thanks,
> 
>  
> 
> Shahar
> 
>  
> 
> 
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