Teledyne LeCroy WaveLink Differential Probe Series (13-25 GHz) - Manual (Page 83)

Operator's Manual
WL-HBW-A-OM-E Rev B 77
Probe Input Impedance and Loading
Attaching any probe to a test circuit adds some loading to the circuit under test. In most applications
the high impedance of the probe, compared to the impedance of the circuit under test, imparts
insignificant load to the test circuit. However, at very high frequencies the capacitive reactance of
the Probe Tip Module or Interconnect Lead may load the circuit enough to affect the measurement.
These probes are designed to minimize these effects at high frequencies. The SI Interconnect Lead
tip uses a construction in which the tip termination consists of a damping resistor with very short
lead length (to minimize inductance) that is soldered to the circuit. These damping resistors connect
to a special distributed resistor on the lead. The distributed resistors compensate for the inherent
transmission loss of the probe system. The result is very broad frequency response with relatively
high impedance. Refer to the figures in this topic for equivalent input circuit information.
These circuits represent the aggregate load placed on the test circuit, but not the actual input circuit
of the probe. For critical applications, you can enter the information of your module or lead into
SPICE or some other simulator to accurately represent the probe loading.
NOTE: To avoid degrading the high frequency performance of the probe do not extend the input
leads on the solder-in interconnect lead tip.