Designing an Interface Between a P6434 Probe and a Target System
P6434 Probe Instructions
27
Loading and Equivalent Circuits
The load presented to the target system by the P6434 probe is low. The load is
equivalent to a 2 pF capacitance with 20 k
Ω
resistance returned to a 2.2 V
supply. The following approximation of the probe loading is sufficient for most
circuit simulation calculations.
Figure 19 shows the equivalent circuit of the P6434 probe. Table 10 shows the
values you can use to calculate characteristics of the lossy delay lines shown in
the next two figures.
Table 10: Lossy delay line values
Characteristic
Value
C (capacitance)
1.58 pF per inch
L (inductance)
8.9 nH per inch
R (resistance)
0.067
Ω
per inch
Z
0
(impedance)
75
Ω
0.005
1.6 nH
0.7 pF
0.005
20 k
Ω
0.23 pF
Length = 58 inches
LOSSY
+2.2 V
1.6 nH
1.1 pF
Ω
Ω
75
Ω
Mictor connector
equivalent circuit
Figure 19: Equivalent circuit for the P6434 probe
