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EE290C - Spring 2004Advanced Topics in Circuit Design
Lecture #3Measurements with VNA and TDRBen Chia
Tu-Th 4 – 5:30pm531 Cory
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Agenda
Relationships between time domain and frequency domainTDR – Time Domain InstrumentVNA – Frequency Domain Instrument
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Time and Frequency Domain Measurement
Relationships between time domain and frequency domainTDR – Time Domain InstrumentVNA – Frequency Domain Instrument
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Time Domain and Frequency Domain
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Time Domain and Frequency Domain
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Time and Frequency Domain Measurement
Relationships between time domain and frequency domainVNA – Frequency Domain InstrumentTDR – Time Domain Instrument
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Agilent 8722ES Vector Network Analyzer
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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
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S Parameter
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Vector Network Analyzer ( VNA )
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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
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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
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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
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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
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STD Definitions from Kit Vendor
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VNA Through Standard Open Standard short Standard
50 ohm Standard
Through StandardOpen Standard
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What is Smith Chart ?
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Open, Short, Load Calibration
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Calibration check : open standard
S22 curve should not go outside of smith chart
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Calibration check : short standard
S22 curve should not go outside of smith chart
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Calibration check : 50 ohm standard
S22 should have onedot in the middle of chart
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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
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S21 of Through Via
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VNA S11 through Via ( Smaller Reflection )
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VNA S21 Stub Via
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S21 Stub Via (red) and Through Via(Yellow)
Stub viaHas
More loss
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S21 of Stub Via ( Larger Reflection )
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VNA Through Via
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VNA Stub Via
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S21 of a 3 inch PCB trace
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S11 of a 3-inch Trace
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S11 of a 4.8" inch PCB trace
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S21 of a 4.8 inch PCB trace
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S11 of 3”(Red) and 4.7”(Yellow) Traced
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Time and Frequency Domain Measurement
Relationships between time domain and frequency domainVNA – Frequency Domain InstrumentTDR – Time Domain Instrument
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Time Domain Reflectometer (TDR)
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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
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Reflection Coefficient
ZLZo
Ei: Incident wave amplitude
Er: Reflected wave amplitude
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Different types of reflections
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TDR Operation
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TTDR
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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
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TDR Plug-in Module
TDR Setup
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TDR screen showing an incident wave leaving TDR
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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
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TDR Reflected Edge of an Open Transmission Line
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TDR Reflected Edge of an short Transmission Line
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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
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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
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TDR: Calibration ProceduresSelect Normalization KeyAdjust Rise timeSelect Normalization and Reference PlaneFollow instructions on the screen
Short and load normalizationTurn on Normalized ChannelDone
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TDR Reference Plane for Calibration
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TDR edge rate 200ps/2ns/4ns
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TDR Impedance Marker
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Crosstalk of two adjacent PCB traces
Channel 2 is not connected
Channel 1 drives open-end pcb trace
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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
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Far End Crosstalk
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Near End Cross Talk
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Differential TDR Reset State
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Differential TDR Reflected wave from an open-end cable
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Differential TDR of trace + connector + trace
ConnectorTDR probing point
Two Traces in parallel
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Differential TDR of trace + connector + trace
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TDR for delay measurement: open-end cable
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TDR connected to an open-end short trace
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63Delay = Time Difference / 2
TDR connected to two open-end short and long traces
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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
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