Specifications

Figure 2-1. Impedance measurement method (3 of 3)
Table 2-1. Common impedance measurement methods
Note: Agilent Technologies currently offers no instruments for the bridge method and the resonant method shaded in the above table.
2-3
DUT
V
x
V
r
High
Low
I
x
I
r
= R
r
Z
x
=
I
x
V
x
V
r
V
x
R
r
Auto-balancing bridge method
Z
x
V
x
= I
x
= I
r
=
R
r
V
r
OSC
Z
x
The current Ix balances with the current Ir which flows through the range
resistor (Rr), by operation of the I-V converter. The potential at the Low point
is maintained at zero volts (thus called a virtual ground.) The impedance of
the DUT is calculated using the voltage measured at the High terminal (Vx)
and across R
r
(Vr).
Note: In practice, the configuration of the auto-balancing bridge differs for
each type of instrument. Generally, an LCR meter, in a low frequency
range typically below 100 kHz, employs a simple operational amplifi-
er for its I-V converter. This type of instrument has a disadvantage in
accuracy at high frequencies because of performance limits of the
amplifier. Wideband LCR meters and impedance analyzers employ
the I-V converter consisting of sophisticated null detector, phase
detector, integrator (loop filter), and vector modulator to ensure a
high accuracy for a broad frequency range over 1 MHz. This type of
instrument can attain to a maximum frequency of 110 MHz.
Advantages Disadvantages Applicable Agilent Common
frequency measurement applications
range instruments
Bridge • High accuracy (0.1% typ.) • Needs to be manually DC to None Standard
method • Wide frequency balanced 300 MHz lab
coverage by using • Narrow frequency
different types of bridges coverage with a
• Low cost single instrument
Resonant • Good Q accuracy up to • Needs to be tuned to 10 kHz to None High Q
method high Q resonance 70 MHz device
• Low impedance measurement
measurement accuracy
I-V • Grounded device • Operating frequency 10 kHz to None Grounded
method measurement range is limited by 100 MHz device
• Suitable to probe-type test transformer used in measurement
needs probe
RF I-V • High accuracy (1% • Operating frequency 1 MHz to 4287A RF
method typ.) and wide range is limited by 3 GHz 4395A+43961A component
impedance range at high transformer used in E4991A measurement
frequencies test head
Network • High frequency • Recalibration required 300 kHz E5071C RF
analysis range when the measurement and above 4395A component
method • Good accuracy when frequency is changed measurement
the unknown • Narrow impedance
impedance is close to measurement range
the characteristic
impedance
Auto- • Wide frequency • Higher frequency ranges 20 Hz to E4980A Generic
balancing coverage from LF to HF not available 110 MHz E4981A component
bridge • High accuracy over 4294A measurement
method a wide impedance
measurement range 4294A+42941A
1
1. Grounded device
• Grounded device 4294A+42942A
1
measurement
measurement