Hi,
I was intrigued by the poor performance of these probes at high frequencies. So I took a closer look.
![](https://www.eevblog.com/forum/projects/high-voltage-differential-probe-design-for-review/?action=dlattach;attach=133953;image)
I measured the response using an RF signal generator and an oscilloscope.
![Broken! :-BROKE](https://www.eevblog.com/forum/Smileys/default/smiliey_scope_broke.gif)
![](https://www.eevblog.com/forum/projects/high-voltage-differential-probe-design-for-review/?action=dlattach;attach=134196;image)
First the gain at 1MHz:
![](https://www.eevblog.com/forum/projects/high-voltage-differential-probe-design-for-review/?action=dlattach;attach=134198;image)
This is correct it is showing a 500x reduction in signal amplitude.
At 44 MHz I found a resonance:
![](https://www.eevblog.com/forum/projects/high-voltage-differential-probe-design-for-review/?action=dlattach;attach=134200;image)
The gain is much higher than it should be, 23.96mV out with 320mV input. That is divide by 13.3 instead of divide by 500.
I noticed that gain was sensitive to the arrangement of the leads.
A quick LTspice model shows that the 7pF capacitance of the probes is resonating with a few uH of inductance.
![](https://www.eevblog.com/forum/projects/high-voltage-differential-probe-design-for-review/?action=dlattach;attach=134202;image)
![](https://www.eevblog.com/forum/projects/high-voltage-differential-probe-design-for-review/?action=dlattach;attach=134204;image)
I am sure that this could be engineered better to dampen this resonance.
![Confused :-//](https://www.eevblog.com/forum/Smileys/default/confused0024.gif)
Regards,
Jay_Diddy_B