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Agilent PN 4294A
New Technologies for Accurate
Impedance Measurement
(40 Hz to 11O MHz)
Product Note
Table of Contents 1. Introduction
1. Introduction .......................................................................2 As the operational frequency and quality of electronic
2. Comparison of Previous Impedance components and materials increases, an impedance
Measurement Techniques ..............................................3 measurement instrument with a wide frequency range and
an exceptional accuracy is required for adequate electrical
3. Features of the Auto-Balancing-Bridge Technique.....4 evaluation.
4. Problems with Previous Auto-Balancing-Bridge
Technique...........................................................................5 The Auto-Balancing-Bridge method (ABB) is widely used
5. Agilent 4294A Solution No. 1: Frequency Expansion ....7 for Low-Frequency (LF) impedance analysis. This technique
has many advantages such as exceptional measurement
6. Agilent 4294A Solution No. 2: Impedance/Phase accuracy and a wide impedance measurement range, but it
Accuracy Improvements ..................................................9 is limited in its frequency coverage.
7. Other New Technology--1: New Impedance Probe .... 11
8. Other New Technology--2: 7-mm Connector Adapter ...12 In this product note, new technologies used in the
Agilent 4294A Precision Impedance Analyzer are discussed.
9. Other New Technology--3: Cable Extension .............13 This impedance analyzer has extended the frequency range
10. Comparison of the Latest Impedance of the ABB technique, and provides new possibilities for LF
Measurement Techniques .............................................14 impedance measurement. The new Auto-Balancing-Bridge
11. Summary ..........................................................................15 method is explained in this product note.
2
2. Comparison of Previous Impedance Measurement Techniques
Table 1 shows the major impedance measurement tech- It is the only technology that can measure at high frequencies
niques as well as the previous frequency ranges covered. (microwave), but the accurate impedance measurement
The Auto-Balancing-Bridge method provides the best range is limited to those impedance values that are close
measurement accuracy and broadest impedance coverage, to the characteristic impedance of the analyzer.
thus permitting its use in all impedance measurement
applications in the LF frequency range. The I-V method In general, applications requiring impedance measurement,
provides unique features in that it can perform measure- such as component and material evaluation, utilize the
ments on a grounded device, as well as probe components ABB technique in the LF frequency range, while the RF I-V
in a circuit. However, the impedance measurement range technique is used in the RF frequency range. Many DUTs
and lower frequency range are limited when compared (Devices Under Test), including capacitors and induc-
with the Auto-Balancing-Bridge method. tors, exhibit an impedance dependency as a function of
frequency. In such cases, a measurement instrument with
The RF I-V method is an enhanced I-V method, which wide frequency coverage is required. As the frequency
successfully expands the frequency range to the GHz coverage of these various techniques increases, the
region. This method is suitable for a broad set of applica- impedance accuracy and impedance measurement range
tions in the RF frequency range. The method, used by must be maintained. Given the history of these techniques,
network analyzers, obtains impedance parameters from innovation of the ABB technique required that the
reflection coefficient measurements. frequency range be expanded in the 4294A.
Table 1: Comparison of previous impedance measurement techniques
Technology Advantage Disadvantage Frequency range Application
Auto-Balancing- Most accurate Wide impedance Limited frequency coverage 5 Hz