5950-3000.pdf

Agilent

Impedance Measurement

Handbook

A guide to measurement

technology and techniques

4 th Edition

Table of Contents

1.0 Impedance Measurement Basics

1.1 Impedance............................................................................................................. 1-1

1.2 Measuring impedance ........................................................................................ 1-3

1.3 Parasitics: There are no pure R, C, and L components ................................. 1-3

1.4 Ideal, real, and measured values ...................................................................... 1-4

1.5 Component dependency factors ....................................................................... 1-5

1.5.1 Frequency .................................................................................................... 1-5

1.5.2 Test signal level........................................................................................... 1-7

1.5.3 DC bias ......................................................................................................... 1-7

1.5.4 Temperature................................................................................................ 1-8

1.5.5 Other dependency factors ......................................................................... 1-8

1.6 Equivalent circuit models of components........................................................ 1-8

1.7 Measurement circuit modes ............................................................................... 1-10

1.8 Three-element equivalent circuit and sophisticated component models.... 1-13

1.9 Reactance chart.................................................................................................... 1-15

2.0 Impedance Measurement Instruments

2.1 Measurement methods ....................................................................................... 2-1

2.2 Operating theory of practical instruments ..................................................... 2-4

LF impedance measurement

2.3 Theory of auto balancing bridge method ......................................................... 2-4

2.3.1 Signal source section................................................................................. 2-6

2.3.2 Auto-balancing bridge section ................................................................. 2-7

2.3.3 Vector ratio detector section.................................................................... 2-8

2.4 Key measurement functions .............................................................................. 2-9

2.4.1 Oscillator (OSC) level ............................................................................... 2-9

2.4.2 DC bias ....................................................................................................... 2-10

2.4.3 Ranging function ....................................................................................... 2-11

2.4.4 Level monitor function ............................................................................ 2-12

2.4.5 Measurement time and averaging .......................................................... 2-12

2.4.6 Compensation function ........................................................................... 2-13

2.4.7 Guarding .................................................................................................... 2-14

2.4.8 Grounded device measurement capability ........................................... 2-15

RF impedance measurement

2.5 Theory of RF I-V measurement method ........................................................... 2-16

2.6 Difference between RF I-V and network analysis measurement methods ... 2-17

2.7 Key measurement functions .............................................................................. 2-19

2.7.1 OSC level .................................................................................................... 2-19

2.7.2 Test port ..................................................................................................... 2-19

2.7.3 Calibration ................................................................................................. 2-20

2.7.4 Compensation ........................................................................................... 2-20

2.7.5 Measurement range .................................................................................. 2-20

2.7.6 DC bias ....................................................................................................... 2-20

3.0 Fixturing and Cabling

LF impedance measurement

3.1 Terminal configuration ...................................................................................... 3-1

3.1.1 Two-terminal configuration ..................................................................... 3-2

3.1.2 Three-terminal configuration................................................................... 3-2

3.1.3 Four-terminal configuration .................................................................... 3-4

3.1.4 Five-terminal configuration ..................................................................... 3-5

3.1.5 Four-terminal pair configuration ............................................................ 3-6

3.2 Test fixtures ......................................................................................................... 3-7

3.2.1 Agilent-supplied test fixtures .................................................................. 3-7

3.2.2 User-fabricated test fixtures .................................................................... 3-8

3.2.3 User test fixture example ......................................................................... 3-9

3.3 Test cables ............................................................................................................ 3-10

3.3.1 Agilent supplied test cables .................................................................... 3-10

3.3.2 User fabricated test cables ...................................................................... 3-11

3.3.3 Test cable extension ................................................................................. 3-11

3.4 Practical guarding techniques .......................................................................... 3-15

3.4.1 Measurement error due to stray capacitances...................................... 3-15

3.4.2 Guarding techniques to remove stray capacitances............................. 3-16

RF impedance measurement

3.5 Terminal configuration in RF region ............................................................... 3-16

3.6 RF test fixtures .................................................................................................... 3-17

3.6.1 Agilent-supplied test fixtures .................................................................. 3-18

3.7 Test port extension in RF region ....................................................................... 3-19

4.0 Measurement Error and Compensation

Basic concepts and LF impedance measurement

4.1 Measurement error ............................................................................................. 4-1

4.2 Calibration ........................................................................................................... 4-1

4.3 Compensation ...................................................................................................... 4-3

4.3.1 Offset compensation ................................................................................. 4-3

4.3.2 Open and short compensations .............................................................. 4-4

4.3.3 Open/short/load compensation .............................................................. 4-6

4.3.4 What should be used as the load? .......................................................... 4-7

4.3.5 Application limit for open, short, and load compensations .............. 4-9

4.4 Measurement error caused by contact resistance ......................................... 4-9

4.5 Measurement error induced by cable extension ............................................ 4-11

4.5.1 Error induced by four-terminal pair (4TP) cable extension ............... 4-11

4.5.2 Cable extension without termination ..................................................... 4-13

4.5.3 Cable extension with termination........................................................... 4-13

4.5.4 Error induced by shielded 2T or shielded 4T cable extension ........... 4-13

4.6 Practical compensation examples .................................................................... 4-14

4.6.1 Agilent test fixture (direct attachment type) ........................................ 4-14

4.6.2 Agilent test cables and Agilent test fixture............................................ 4-14

4.6.3 Agilent test cables and user-fabricated test fixture (or scanner)....... 4-14

4.6.4 Non-Agilent test cable and user-fabricated test fixture....................... 4-14

RF impedance measurement

4.7

Calibration and compensation in RF region ................................................. 4-16

4.7.1 Calibration ................................................................................................ 4-16

4.7.2 Error source model ................................................................................. 4-17

4.7.3 Compensation method ............................................................................ 4-18

4.7.4 Precautions for open and short measurements in RF region ........... 4-18

4.7.5 Consideration for short compensation ................................................ 4-19

4.7.6 Calibrating load device ........................................................................... 4-20

4.7.7 Electrical length compensation ............................................................. 4-21

4.7.8 Practical compensation technique ........................................................ 4-22

4.8

Measurement correlation and repeatability .................................................. 4-22

4.8.1 Variance in residual parameter value .................................................. 4-22

4.8.2 A difference in contact condition ......................................................... 4-23

4.8.3 A difference in open/short compensation conditions ....................... 4-24

4.8.4 Electromagnetic coupling with a conductor near the DUT ............... 4-24

4.8.5 Variance in environmental temperature............................................... 4-25

5.0 Impedance Measurement Applications and Enhancements

5.1 Capacitor measurement ................................................................................... 5-1

5.1.1 Parasitics of a capacitor .......................................................................... 5-2

5.1.2 Measurement techniques for high/low capacitance............................ 5-4

5.1.3 Causes of negative D problem ................................................................ 5-6

5.2 Inductor measurement ..................................................................................... 5-8

5.2.1 Parasitics of an inductor ......................................................................... 5-8

5.2.2 Causes of measurement discrepancies for inductors ......................... 5-10

5.3 Transformer measurement .............................................................................. 5-14

5.3.1 Primary inductance (L1) and secondary inductance (L2) ................. 5-14

5.3.2 Inter-winding capacitance (C)................................................................ 5-15

5.3.3 Mutual inductance (M) ............................................................................ 5-15

5.3.4 Turns ratio (N) .......................................................................................... 5-16

5.4 Diode measurement .......................................................................................... 5-18

5.5 MOS FET measurement .................................................................................... 5-19

5.6 Silicon wafer C-V measurement ...................................................................... 5-20

5.7 High-frequency impedance measurement using the probe ......................... 5-23

5.8 Resonator measurement ................................................................................... 5-24

5.9 Cable measurements ......................................................................................... 5-27

5.9.1 Balanced cable measurement ................................................................. 5-28

5.10 Balanced device measurement ........................................................................ 5-29

5.11 Battery measurement ....................................................................................... 5-31

5.12 Test signal voltage enhancement .................................................................... 5-32

5.13 DC bias voltage enhancement .......................................................................... 5-34

5.13.1 External DC voltage bias protection in 4TP configuration............... 5-35

5.14 DC bias current enhancement ......................................................................... 5-36

5.14.1 External current bias circuit in 4TP configuration ........................... 5-37

5.15 Equivalent circuit analysis function and its application ............................ 5-38

iii

Appendix A: The Concept of a Test Fixture’s Additional Error ............. A-1

A.1 System configuration for impedance measurement ...................................... A-1

A.2 Measurement system accuracy .......................................................................... A-1

A.2.1 Proportional error ..................................................................................... A-2

A.2.2 Short offset error ....................................................................................... A-2

A.2.3 Open offset error........................................................................................ A-3

A.3 New market trends and the additional error for test fixtures ...................... A-3

A.3.1 New devices ................................................................................................ A-3

A.3.2 DUT connection configuration................................................................. A-4

A.3.3 Test fixture’s adaptability for a particular measurement ................... A-5

Appendix B: Open and Short Compensation ......................................................... B-1

Appendix C: Open, Short, and Load Compensation ......................................... C-1

Appendix D: Electrical Length Compensation ...................................................... D-1

Appendix E: Q Measurement Accuracy Calculation ...................................... E-1

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