EE290C - Spring 2004 Advanced Topics in Circuit Design

Transcription

1 EE290C - Spring 2004 Advanced Topics in Circuit Design Lecture #3 Measurements with VNA and TDR Ben Chia Tu-Th 4 5:30pm 531 Cory Agenda Relationships between time domain and frequency domain TDR Time Domain Instrument VNA Frequency Domain Instrument 2

2 Time and Frequency Domain Measurement Relationships between time domain and frequency domain TDR Time Domain Instrument VNA Frequency Domain Instrument 3 Time Domain and Frequency Domain 4

3 Time Domain and Frequency Domain 5 Time and Frequency Domain Measurement Relationships between time domain and frequency domain VNA Frequency Domain Instrument TDR Time Domain Instrument 6

4 Agilent 8722ES Vector Network Analyzer 7 Vector Network Analyzer ( VNA ) A frequency Domain Instrument Sin wave generators on all ports Receive Sampling circuit on all ports Need Calibration Can measure delay, loss at different frequencies 8

5 S Parameter 9 Vector Network Analyzer ( VNA ) 10

6 VNA Setup Warm up the VNA for one hour Connect RF cables with torque wrench Set start and stop frequency Set number of sampling point Set the average to 4 Start Calibration. 11 What is the purpose of VNA calibration? Establish reference plane Remove any unwanted measurement error, including cable and connections Short/open/load standard Through standard Reference Plane 12

7 What is reference plane? VNA will measure the response starting at the reference plane SMA Connector Reference plane Coax Connected to VNA PCB trace or Device Under Test Calibration remove all loss, delay, reflection from the measurement results before this plane 13 VNA 3.5MM SMA Calibration Enter Calibration Kit standard table Cal Cal Kit Modify[2.4mm] Define Standard Modify STD Definition Specify Offset Offset Delay Calibrate VNA with Open, Short, Load Standards Cal Calibrate Menu Full two port Reflection Check the validity of calibration Measure Standard Cal Kit Measure known transmission line 14

8 STD Definitions from Kit Vendor 15 VNA Through Standard Open Standard short Standard 50 ohm Standard Open Standard Through Standard 16

9 What is Smith Chart? 17 Open, Short, Load Calibration 18

10 Calibration check : open standard S22 curve should not go outside of smith chart 19 Calibration check : short standard S22 curve should not go outside of smith chart 20

11 Calibration check : 50 ohm standard S22 should have one dot in the middle of chart 21 PCB Through and stub Via Pcb surface layer trace PCB cross section Ch#1 Ch#2 Through via Pcb surface layer trace Ch#1 Ch#2 Stub via 22

12 S21 of Through Via 23 VNA S11 through Via ( Smaller Reflection ) 24

13 VNA S21 Stub Via 25 S21 Stub Via (red) and Through Via(Yellow) Stub via Has More loss 26

14 S21 of Stub Via ( Larger Reflection ) 27 VNA Through Via 28

15 VNA Stub Via 29 S21 of a 3 inch PCB trace 30

16 S11 of a 3-inch Trace 31 S11 of a 4.8" inch PCB trace 32

17 S21 of a 4.8 inch PCB trace 33 S11 of 3 (Red) and 4.7 (Yellow) Traced 34

18 Time and Frequency Domain Measurement Relationships between time domain and frequency domain VNA Frequency Domain Instrument TDR Time Domain Instrument 35 Time Domain Reflectometer (TDR) 36

19 TDR: Time Domain Reflectometer TDR is time domain instrument based on the principle of wave reflections Used mainly for Impedance measurement Can measure propagation delay TDR needs require calibration before use 37 Reflection Coefficient Ei: Incident wave amplitude Er: Reflected wave amplitude Zo ZL 38

20 Different types of reflections 39 TDR Operation TDR T D 40

21 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 41 TDR Plug-in Module TDR Setup 42

22 TDR screen showing an incident wave leaving TDR 43 TDR with open-end cable This circle is shown on the next page) Reflected wave seen by TDR Incident wave Round trip delay time of coax cable 44

23 TDR Reflected Edge of an Open Transmission Line 45 TDR Reflected Edge of an short Transmission Line 46

24 What is the purpose of TDR calibration? Calibration establishes the starting point of the wave, which is also the start time of the measurement 50 ohm cable To TDR SMA Connector Wave direction Reference plane ( wave starting point ) How does the TDR know this is the starting point? 47 By a known standard at the reference plane Short = cable connected to ground 50 ohm = cable connected to 50 ohm load To TDR SMA Connector Short standard 50 ohm cable To TDR 50 ohm cable SMA Connector 50 ohm standard 48

25 TDR: Calibration Procedures Select Normalization Key Adjust Rise time Select Normalization and Reference Plane Follow instructions on the screen Short and load normalization Turn on Normalized Channel Done 49 TDR Reference Plane for Calibration 50

26 TDR edge rate 200ps/2ns/4ns 51 TDR Impedance Marker 52

27 Crosstalk of two adjacent PCB traces Channel 1 drives open-end pcb trace Channel 2 is not connected 53 Cross Talk TDR Channel #1(stimulus) 50 ohm TDR Channel #1(stimulus) TDR Channel #2 Far End Cross Talk TDR Channel #2 Near End Cross Talk 50 ohm 54

28 Far End Crosstalk 55 Near End Cross Talk 56

29 Differential TDR Reset State 57 Differential TDR Reflected wave from an open-end cable 58

30 Differential TDR of trace + connector + trace Connector TDR probing point Two Traces in parallel 59 Differential TDR of trace + connector + trace 60

31 TDR for delay measurement: open-end cable 61 TDR connected to an open-end short trace 62

32 TDR connected to two open-end short and long traces Delay = Time Difference / 2 63 Summary TDR measures signal in the time domain VNA measures signal in the frequency domain Both TDR and VNA requires Calibration to determine the reference plane and to remove measurement errors Reference Test and Meaurement Library 64