1

EE290C - Spring 2004Advanced Topics in Circuit Design

Lecture #3Measurements with VNA and TDRBen Chia

Tu-Th 4 – 5:30pm531 Cory

2

Agenda

Relationships between time domain and frequency domainTDR – Time Domain InstrumentVNA – Frequency Domain Instrument

2

3

Time and Frequency Domain Measurement

Relationships between time domain and frequency domainTDR – Time Domain InstrumentVNA – Frequency Domain Instrument

4

Time Domain and Frequency Domain

3

5

Time Domain and Frequency Domain

6

Time and Frequency Domain Measurement

Relationships between time domain and frequency domainVNA – Frequency Domain InstrumentTDR – Time Domain Instrument

4

7

Agilent 8722ES Vector Network Analyzer

8

Vector Network Analyzer ( VNA )

A frequency Domain InstrumentSin wave generators on all portsReceive Sampling circuit on all portsNeed CalibrationCan measure delay, loss at different frequencies

5

9

S Parameter

10

Vector Network Analyzer ( VNA )

6

11

Warm up the VNA for one hourConnect RF cables with torque wrenchSet start and stop frequencySet number of sampling pointSet the average to 4Start Calibration….

VNA Setup

12

What is the purpose of VNA calibration?

Establish reference planeRemove any unwanted measurement error, including cable and connections

Reference Plane

Short/open/load standard

Through standard

7

13

What is reference plane? VNA will measure the response starting at the reference plane

PCB trace or Device Under Test

SMA Connector

Coax Connected to VNA

Reference plane

Calibration remove all loss, delay, reflection… from the measurement results before this plane

14

Enter Calibration Kit standard tableCal Cal Kit Modify[2.4mm] Define Standard Modify STD Definition Specify Offset Offset Delay …

Calibrate VNA with Open, Short, Load StandardsCal Calibrate Menu Full two port Reflection …

Check the validity of calibrationMeasure Standard Cal KitMeasure known transmission line

VNA 3.5MM SMA Calibration

8

15

STD Definitions from Kit Vendor

16

VNA Through Standard Open Standard short Standard

50 ohm Standard

Through StandardOpen Standard

9

17

What is Smith Chart ?

18

Open, Short, Load Calibration

10

19

Calibration check : open standard

S22 curve should not go outside of smith chart

20

Calibration check : short standard

S22 curve should not go outside of smith chart

11

21

Calibration check : 50 ohm standard

S22 should have onedot in the middle of chart

22

PCB Through and stub Via

Pcb surface layer trace PCB cross section

Pcb surface layer trace

Stub via

Through via

Ch#1 Ch#2

Ch#2Ch#1

12

23

S21 of Through Via

24

VNA S11 through Via ( Smaller Reflection )

13

25

VNA S21 Stub Via

26

S21 Stub Via (red) and Through Via(Yellow)

Stub viaHas

More loss

14

27

S21 of Stub Via ( Larger Reflection )

28

VNA Through Via

15

29

VNA Stub Via

30

S21 of a 3 inch PCB trace

16

31

S11 of a 3-inch Trace

32

S11 of a 4.8" inch PCB trace

17

33

S21 of a 4.8 inch PCB trace

34

S11 of 3”(Red) and 4.7”(Yellow) Traced

18

35

Time and Frequency Domain Measurement

Relationships between time domain and frequency domainVNA – Frequency Domain InstrumentTDR – Time Domain Instrument

36

Time Domain Reflectometer (TDR)

19

37

TDR: Time Domain Reflectometer

TDR is time domain instrument based on the principle of wave reflectionsUsed mainly for Impedance measurementCan measure propagation delayTDR needs require calibration before use

38

Reflection Coefficient

ZLZo

Ei: Incident wave amplitude

Er: Reflected wave amplitude

20

39

Different types of reflections

40

TDR Operation

D

TTDR

21

41

TDR Calibration Procedure •Turn on TDR for 30 minutes before measurement•Prepare Calibration Standard•Short standard and 50 ohm standard

•Get good quality RF cables•Discharge cables before connecting to TDR •Select TDR mode of operation•Push “TDR Setup”•Turn on Stimulus

42

TDR Plug-in Module

TDR Setup

22

43

TDR screen showing an incident wave leaving TDR

44

TDR with open-end cable

Incident wave

Reflected wave seen by TDR

This circle is shown on the next page)

Round trip delay time of coax cable

23

45

TDR Reflected Edge of an Open Transmission Line

46

TDR Reflected Edge of an short Transmission Line

24

47

What is the purpose of TDR calibration? Calibration establishes the starting point of the wave, which isalso the start time of the measurement

SMA Connector

50 ohm cable

Reference plane ( wave starting point )

How does the TDR know this is the starting point?

Wave direction

To TDR

48

By a known standard at the reference planeShort = cable connected to ground50 ohm = cable connected to 50 ohm load

50 ohm standard

Short standard

SMA Connector

50 ohm cable

To TDR

SMA Connector

50 ohm cable

To TDR

25

49

TDR: Calibration ProceduresSelect Normalization KeyAdjust Rise timeSelect Normalization and Reference PlaneFollow instructions on the screen

Short and load normalizationTurn on Normalized ChannelDone

50

TDR Reference Plane for Calibration

26

51

TDR edge rate 200ps/2ns/4ns

52

TDR Impedance Marker

27

53

Crosstalk of two adjacent PCB traces

Channel 2 is not connected

Channel 1 drives open-end pcb trace

54

Cross Talk

50ohm

TDR Channel #1(stimulus)

TDR Channel #2

50ohm

TDR Channel #1(stimulus)

TDR Channel #2

Far End Cross Talk

Near End Cross Talk

28

55

Far End Crosstalk

56

Near End Cross Talk

29

57

Differential TDR Reset State

58

Differential TDR Reflected wave from an open-end cable

30

59

Differential TDR of trace + connector + trace

ConnectorTDR probing point

Two Traces in parallel

60

Differential TDR of trace + connector + trace

31

61

TDR for delay measurement: open-end cable

62

TDR connected to an open-end short trace

32

63Delay = Time Difference / 2

TDR connected to two open-end short and long traces

64

Summary

TDR measures signal in the time domainVNA measures signal in the frequency domainBoth TDR and VNA requires Calibration to determine the reference plane and to remove measurement errorsReference

www.agilent.com Test and Meaurement Library