Tutorial Session 8:00 am Feb. 2, 2009 Robert Schaefer, Agilent Technologies Feb. 2, 2009
Objectives Present Advanced Calibration Techniques Summarize Existing Techniques Present New Advanced Calibration Methods Discuss Calibration and Measurement Problems and solutions Probed Measurements and Calibration Multiport Measurements and Calibration 2
Advanced Calibration TRL Cal Kit Design and Verification Wizard 2 Tier TRL calibration and De-embedding Automatic Fixture Removal Differential Cross Talk Calibration Multiport & Probed Measurement and Calibration Challenges Cal Set Viewing and Refresh Calibration Probe Calibration Wizard Diagnostic Example 3
Al/ Tom presented Manual Process Presented the need for TRL calibration Presented good design with excellent results Discussed how to verify the performance of cal kit New TRL wizard in PLTS Makes this process much easier Provides added insight Easily review previous results 4
Load previous set Design Calibration Measurement Verification Analysis Easy download to PNA 5
Easy to use Specify: cal kit name, connector type, and description for downloading to PNA 6
Automatically determines default: frequency range, cal type, and cal kit. User can easily change defaults. 7
Leads user through measurements of each cal standard in TRL kit Or Load previous measurements. 8
Verifies actual frequency ranges of standards and compares to design goals. Easy to update the cal kit definition. 9
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Expected performance Repeatability After TRL calibration 11
Cal kit definition: Kept up to date Easy to change One click download to PNA 12
Normally a SOLT/ECal removes the adapter Originally used for non-insertable devices An adapter is needed to provide thru calibration Like doing two calibrations to remove the effects of the adapter A TRL for one port and ECal (SOLT) for one port One port is ECal (coax reference) Second port is TRL (TRL reference center of thru) After completing the adapter removal cal, measure the thru. The result is ½the thru, which is the fixture. Save the.s2p file and you have the de-embed file Measure your DUT (with fixtures) and de-embed with file created above 13
To PNA To PNA Fixture Fixture ECal Reference Plane port 1 TRL Reference Plane port 2 14
The blue trace is a measurement of a backplane with fixture cards (red circle). The red trace is the same measurement with a TRL calibration fixture removed. The green trace is the blue trace with fixture de-embedded (S2p file from 2-tier calibration. De-embed TRL Ecal 15
Left Half Fixture Right Half Fixture DUT THRU fixture Connect left and right fixture halves. 16
Assumptions: Symmetric right to left Symmetric top to bottom No mode conversion Steps: 1.Calibrate at cable ends (4-port) 2.Measure fixture and save file 3.Measure fixtured DUT 4.Remove fixture Technique presented in paper at Design Con 2007 by Vahe Adamian 17
Open a 4 port DUT+Thru Fixture file in PLTS (Only 4 port is supported) In PLTS Menu Utilities Automatic Fixture Removal Select a Thru Fixture file, then Apply, the thru Fixture will be removed from opened DUT+Thru Fixture file. 18
4-port TRL Calibration Technique Fixture may be asymmetric Similar assumptions to single ended TRL Repeatability of connector, launch, and line lines are usable 20 to 160 degrees relative to thru Additional Differential Constraints SDDnm and SCDnm < -30 db Skew between lines < 10 degrees Open DUT Thru Line 3 Line 2 Line 1 19
PNA Cal Blue Thru Fixture Removal - Red Differential Crosstalk Cal - Green PNA Cal Blue Thru Fixture Removal - Red Differential Crosstalk Cal - Green Differential Crosstalk cal and Fixture removal give very similar results, removing the effect of the fixtures. Measuring the resonance incorrectly can imply significantly more loss that really exists in the device. 20
PNA Cal Blue Thru Fixture Removal - Red Differential Crosstalk Cal - Green PNA Cal Blue Thru Fixture Removal - Red Differential Crosstalk Cal - Green Offset is due to coupling that was ignored in the single ended calibration. 21
Probe calibrations are more prone to errors than coaxial calibrations and can take a longer time to complete. Multiport calibrations have many standards to connect multiple times and are also prone to errors. Ecal calibrations are less prone to errors. Help is needed in verifying these calibrations and recovering from an error with the least amount of additional time and work. 22
The first step is to be able to look at all the computed error terms to check for errors. Second is being able to look at the measurements of the individual cal standards to help find which one(s) are bad. Third, a quick way to repair (refresh) the bad calibration is needed 23
1. Load calset from PNA. 2. Inspect error terms. 24
1. Scroll through traces. 2. Problem with port 5. 3. Directivity is bad - probably load measurement. 25
1. Indeed it looks like the load on port 5 was wrong. 26
1. Indeed it looks like the load on port 5 was wrong. 2. Switching to polar or smith chart views will show a short was connected by mistake. 27
1. Browse to saved file with standards measurements. 2. Download raw measurements to PNA 28
1. Re-measure just the bad standard 2. Click Next to re-calculate error terms. 3. Ready to Measure DUT. 29
Creating Cal Kit definitions for probes and substrates can be challenging. Finding data that came with probes Multiple calibration standards on the ISS Loop back thrus for dual probes Multiport Calibration Challenges Grouping of cal steps Custom bitmaps for clarity 30
1. Use Straight Thru for the thru definitions. 2. Then specify Unknown Thru for loop back thru paths for best accuracy. 31
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Two connector types will be created in the cal kit. Use one connector type for the upper two ports, another for the lower two ports. 33
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Use an existing design (differential) Try automatic fixture removal with a thru artifact Quantify its characteristics Compare with single ended TRL Use data from multiple domains to better understand what we have Troubleshooting the measurement issue 35
0.25 1.75 1.00 TRL Reference Plane 36
TRL Reference Plane 37
Good repeatability of connectors, launches, and line impedance Phase Skew is less than 10 degrees (8 degrees) 38
Mode conversion is less than 30 db Differential match nearly symmetric 39
Appears to be a problem with differential port 2 more ringing Appears to be a problem with single ended port 2 connector 40
Resonance in S21 path 41
Automatic Fixture removal also removes coupling SOLT Calibration includes fixture TRL calibration removes fixture but not coupling 42
Automatic Fixture removal also removes coupling. TRL calibration removes fixture but not coupling. SOLT Calibration includes fixture. 43
Discussed additional calibration and fixture removal techniques beyond single ended TRL Discussed some problems and solutions for probed measurements and multimode measurements Provided some insight into analysis of measurements. 44