Test and Measurement
Figure 4: With two
parallel transmission
lines, the
characteristic
impedance of the
combined
transmission line is the
parallel combination
Issue VIII 2009
of each transmission
square4
line’s characteristic
.com
impedances
Figure 2: C-V measurement connection scheme of the two transmission lines that are sharing
for Kelvin connections the inner shield.
Taking these two transmission line concepts
into account, Keithley has developed a cabling
kit that supports making I-V, C-V and pulsed I-V
oasiasemiconductor
measurements with the same set of cables. This
.eur
reduces the effort required from operators of
www
parameter analyzer systems, who would
otherwise be forced to go through the laborious
27
Figure 3: Pulse testing connection scheme process of re-cabling the connections from the
for Kelvin connections bulkhead/feedthrough to the probe tips each
time it was necessary to switch to a new
measurement type. Versions of the cable kit are
Characteristic Impedances available for use with probers made by Cascade
Given the challenges created by these differing Microtech probers and SUSS MicroTec. Both
cabling requirements for different measurement versions are designed to work with a coaxial
types, Keithley has developed a multi- Kelvin probe head only. Table 1. Cable
measurement cabling system based on an requirements for I-V,
understanding of two transmission concepts. The Cabling System Overview C-V, and Pulsed I-V
first concept is that if there are two parallel Figure 7 illustrates how a DUT can be connected measurements
transmission lines, the characteristic impedance
of the combined transmission line is the parallel
Cable requirements for I V, C V, and Pulsed I V measurements
combination of each transmission line’s
characteristic impedances, as shown in Figure 4. DC I V measurements
The second transmission line concept is that ring6 Triaxial cables
if there are two transmission lines connected in ring6 Kelvin connection
series, as shown in Figure 5, the characteristic ring6 Isolated, driven guards
impedance of the combined transmission line is
the sum of the characteristic impedances of the LCR/C V measurements
two individual transmission lines. ring6 Coaxial cables
This series arrangement can be observed in ring6 Kelvin connection
a triaxial cable, as shown in Figure 6. A triaxial ring6 Shields connected at the probe tips
cable is actually two concentrically arranged
transmission lines. The inner shield and the Pulsed I V measurements
center conductor form one transmission line (Z
1
) ring6 Coaxial cables
and the inner shield and the outer shield form a ring6 Non-Kelvin connection (single cable)
second transmission line (Z
2
). The centre ring6 Shields connected at the probe tips
conductor to outer shield interaction has a ring6 Shield optionally connected to a probe tip
characteristic impedance (Z
S
) equal to the sum
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