Agilent Technologies 4395A - Page 399

I-V
Measurement
Method
Impedance Measurement
Basics
I-V
Measurement
Method
Basic
Concept
of
I-V
Method
Figure
A
-14.
I-V
Measurement
Method
The
unknown
impedance
,Z,
can
be
calculated
from
the
measured
voltage
and
current
using
Ohm's
law:
(See
circuit
Ain
Figure
A
-14
.)
Z
=
V
I
The
current,
I ,
can be
also
obtained
by
the
voltage
level
of
the
known
resistance
,
R
0
.
Z
=
V
1
I
=
V
1
V
2
R
0
See
circuit
B
in
Figure
A
-14
.
The
4395A
uses
circuit
B
to
determine
the
unknown
impedance
.
How This Is Dierent From Impedance Conversion in the Network
Analyzer
Mode
The network
analyzer part of the 4395A has an impedance conversion feature that converts
the reection coecient
to impedance
. The reection is determined by the impedance of the
DUT.
Z = R
0
1 0 0
1+0
( 0 1  0 
1)
If the DUT impedance is equal to the characteristic impedance, there is no reection. When the
impedance is an innite value like OPEN, the all input signal is reected.
When the impedance is greater than characteristic impedance, the measurement error is
increased. For example, for an impedance of 2 k, a 1 percent error in the reection coecient
is converted to a 24 percent error in impedance.
Basic Measurement Theory A-23