Probes - HBM Genesis GEN5i User Manual

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D.5 10X Probes
10X probes (also called 10:1 probes, divider probes, or attenuating probes)
have a resistor and capacitor (in parallel) inserted into the probe. Figure D.15
shows the circuit for the 10X probe connected to a high-impedance input of an
instrument.
Figure D.15: Input connected using a 10X probe
If R1C1 = R2C2, then this circuit has the result that the effect of both capacitors
exactly cancel. The capacitor is usually made adjustable and can be tweaked
for a near perfect match. Under these conditions, the relationship of VS to VIN
is:
R2 is the input resistance of the instrument's high input impedance (1 MΩ) and
R1 = 9R2. From the previous equation, this results in:
So the final result is a probe / instrument input combination that has a much
wider bandwidth than the 1X probe, due to the effective cancellation of the two
capacitors. However, the instrument now sees only one-tenth of the original
voltage (hence the name 10X probe). Also notice that the circuit being
measured sees a load impedance of R1 + R2 = 10 MΩ, which is much higher
than with the 1X probe.
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