1. Precision Time-Domain Reflectometry: Helping to solve today’s difficult signal integrity/transmission problems October 2003

2. TDR Customer Presentation, Oct ‘03 Page 2 Agenda 1. Brief TDR review Some new things and some old things seen in a new way 2. Advanced calibration techniques unique to Agilent 3. New techniques for improved 2-event resolution and impedance accuracy 4. S-parameter results from the TDR Where to find out more: New Application Note (see last slide)

3. TDR Customer Presentation, Oct ‘03 Page 3 1. What is TDR? Time domain reflectometry Analyze the quality of high- speed components and channels for transmission quality Are there any reflections due to impedance discontinuities? How big are they? Where are they? Incident energy Transmitted energy Reflected energy

4. TDR Customer Presentation, Oct ‘03 Page 4 TDR: Launch a fast step into the DUT and measure anything that reflects back ZLZL EiEi ErEr STEP GENERATOR OSCILLOSCOPE TRANSMISSION SYSTEM UNDER TEST Typical Step: 200 mV, 250 kHz ‘square wave’ with 35 ps rise time Incident energy Transmitted energy Reflected energy

5. TDR Customer Presentation, Oct ‘03 Page 5 What is TDR? Launch a fast pulse into the device under test Measure what reflects back from the DUT The size and polarity of any reflections indicates the magnitude of any discontinuity The time it takes for the reflection to return is used to indicate the location of any discontinuity Input pulse Reflected pulse(s) Transmission lines with changing impedance

6. TDR Customer Presentation, Oct ‘03 Page 6 Displaying impedance in the Time Domain: TDR provides “Instantaneous Impedance” Typical TDR result A: 50 Ohm cable B: Launch to microstrip C: 50 Ohm microstrip D: 75 Ohm microstrip E: 50 Ohm microstrip F: “open” circuit A B C D E F Compare to a network analyzer which provides impedance as a function of frequency

7. TDR Customer Presentation, Oct ‘03 Page 7 2. Some important advantages of the 86100 TDR Would you buy a network analyzer without a calibration kit? No! Without calibration we are forced to rely completely on the raw performance of the instrument and have no ability to remove error causing mechanisms outside the instrument that are in the measurement path DUT

8. TDR Customer Presentation, Oct ‘03 Page 8 Systematic TDR measurement errors can be removed through simple calibration A simple concept: By placing known reflections on the system, the measurement errors can be identified and removed Simple to perform: Connect a short and a load at the reference plane Errors caused by cabling, attenuation etc. can be removed from the measurement Agilent is the only provider to use Normalization. Test FixtureDevice Under Test Blue Trace - Normalized Green Trace - Standard Error = 2.3 ohms

9. TDR Customer Presentation, Oct ‘03 Page 9 What arguments might you hear against this? “We don’t need fancy calibrations. We have a precision airline inside the TDR” But what can you do for error mechanisms beyond the TDR output? Agilent doesn’t need to do a calibration either, unless there is something beyond the TDR output that degrades the results (which, in real life, there almost always is) “Calibration is a weak excuse for bad hardware” Calibration techniques are a proven route to a better measurement Can you imagine doing network analysis without a good calibration process? This is all explained in more detail in the new Application Note (see last slide)

10. TDR Customer Presentation, Oct ‘03 Page 10 3. Some problems the industry faces….. Data speeds are getting faster in electrical circuits Devices are getting smaller and more complex As edge speeds increase, more high-frequency energy is present More difficult to control impedance

11. TDR Customer Presentation, Oct ‘03 Page 11 The edgespeed of the TDR step sets two important measurement levels The two-event resolution (how close can two reflections be and still be seen as separate events) Closely spaced reflections can get blurred together Two-event resolution set by material velocity and TDR system risetime How accurate is the measurement of the reflection magnitude As step speeds increase, more high frequency content Reflections often get worse Reflections for a 20 ps edge can be much larger than a 35 ps edge

12. TDR Customer Presentation, Oct ‘03 Page 12 A 35 picosecond step is insufficient to see closely spaced reflections With a 35 ps step, all you know is the device is there If there is more than one reflection, we can’t tell 35ps

13. TDR Customer Presentation, Oct ‘03 Page 13 High resolution allows your customers to see what they could never see before At 9 ps step speed, we see 5 separate reflections Each event is easily seen and quantified 9ps V-connector pin-collette V-connector pin-collette hermetic feedthrough coaxial feed- through microstrip transmission line coaxial- microstrip launch

14. TDR Customer Presentation, Oct ‘03 Page 14 A faster step often yields a higher reflection magnitude At 35 ps, the reflections look very small (~52 Ohms) At 9 ps the reflections increase to over 58 Ohms The 35 ps result isn’t necessarily wrong and the 9 ps right Test at an edge speed similar to how the device will be used Some examples 20 to 35 ps for 10 Gb/s 5 to 12 ps for 40 Gb/s Designers working at the very high data rates or with very small devices need a very fast TDR

15. TDR Customer Presentation, Oct ‘03 Page 15 How can I test faster than the 35 ps the TDR is specified at? Two choices Digitally increase the edge speed through some signal processing “Normalization calibration” (discussed earlier) can use DSP to enhance the effective edge speed Can decrease the risetime to less than 20 ps Electrically speed up the pulse Use external hardware to produce a much faster edge

16. TDR Customer Presentation, Oct ‘03 Page 16 86100/Picosecond Pulse Labs 4020 Measurement capabilities 35ps <9ps The Picosecond Pulse Labs 4020 modules takes the 35 Picosecond pulse from the Agilent TDR and increases the speed to under 9 picoseconds Two-event resolution is improved by a factor of 4! (1.5 mm ‘air’, less than 1 mm in common dielectrics)

17. TDR Customer Presentation, Oct ‘03 Page 17 Optimizing Measurements You will lose your edge speed if you have: Excess or poor quality cabling to and from the DUT The scope receiver channel has insufficient BW Recommend TDR with the 86118A ~75 GHz remote plug-in: Max. bandwidth Minimum cabling distances 4020 Remote TDR Head Sampling Port Device Under Test 54754A TDR module 86118A

18. TDR Customer Presentation, Oct ‘03 Page 18 Configuring a system 86100 A or B mainframe (3.05 FW or above) 54754A TDR plug-in 86118A 70 GHz plug-in Lower BW channels can be used, but edgespeed and resolution will be reduced Cabling between the DUT and the receive channel degrades TDR speed Picosecond 4020 TDR or TDT enhancement module

19. TDR Customer Presentation, Oct ‘03 Page 19 Using the 4020 with TDR’s that don’t use Normalization PSPL 4020 works with other TDRs: Significant pulse aberrations. Cannot be calibrated out If pulse aberrations are not removed, they can be misinterpreted as close-in reflections 86100 TDR calibration significantly improves the 4020 pulse quality Normalization also provides an excellent way to eliminate fixturing errors TDR without Normalization 4020 pulse 86100 4020 pulse

20. TDR Customer Presentation, Oct ‘03 Page 20 4. Frequency domain analysis is critical for completely understanding device performance DUT Incident wave Reflected wave Transmitted wave S 11 S 21 Incident wave Reflected wave Transmitted wave TDR TDT t t DUT

21. TDR Customer Presentation, Oct ‘03 Page 21 Benefits of S-parameter analysis Some things are just easier to see in the frequency domain Resonances Frequency response Device modeling can be more accurate with frequency domain data Some critical measurements of differential devices are better understood as a function of frequency “There is no fundamental difference in the information content between the time domain and the frequency domain” Eric Bogatin Chief Technical Officer GigaTest Labs

22. TDR Customer Presentation, Oct ‘03 Page 22 Changing the way high speed digital customers view VNA’s “Everything you ever wanted to know about your device… and more” DUT VNA covers all combinations of in, out, reflections, & crosstalk. All combinations contained in a 16 element matrix for a 4 port DUT.

23. TDR Customer Presentation, Oct ‘03 Page 23 For differential circuits, frequency domain analysis helps even more Differential are circuits becoming more important at high speeds Differential behavior can be much different than viewing each port individually (there is transmission line coupling designed in ) Differential circuits reduce emissions and are less susceptible to radiation Like making the cross- talk work for you. Port 1 Port 2 Balanced (Differential) devices can be analyzed as pairs (Mixed-Mode S-parameters) rather than single ended Differential Common Less far field emissions (crosstalk) More cancellation of incoming interference

24. TDR Customer Presentation, Oct ‘03 Page 24 What About Non-Ideal Devices? Undesirable mode conversions cause emission or susceptibility problems Differential-stimulus to common-response conversion + Common-stimulus to differential-response conversion EMI Generation EMI Susceptibility + = = Imperfectly matched lines mean the electromagnetic fields of the signals are not as well confined as they should be – giving rise to generation of interference to neighboring circuits. Imperfectly matched lines mean that interfering signals do not cancel out completely when subtraction occurs at the receiver. Measured by stimulating common-mode to simulate interference.

25. TDR Customer Presentation, Oct ‘03 Page 25 S-Parameters describe differential well. Four quadrants of differential/common mode S parameters: S (response,stimulus,output,input) Example S CD21 : Drive port 1 differentially and measure what has been converted to common mode at port 2

26. TDR Customer Presentation, Oct ‘03 Page 26 Everything you ever wanted to know….. Single ended S Parameters Mixed Mode S Parameters Mixed Mode S Parameters Displayed in the Time Domain Frequency domain s-parameters can be used to gain insight in frequency domain plots and time domain views.

27. TDR Customer Presentation, Oct ‘03 Page 27 VNA, TDR, or both? All of the S-parameter data available using the Physical Layer Test System (PLTS) is now available using the 86100 TDR! N1930A Controls 86100 TDR Guided setup and calibration Automatic deskew Conversion of TDR data to complete S parameter results

28. TDR Customer Presentation, Oct ‘03 Page 28 “True” differential measurements Some TDRs make a big deal of producing both a negative and a positive step for doing differential TDR. “True” differential Agilent produces only positive pulses and then uses math to build a differential measurement A differential system has coupled lines. The electromagnetic fields will be very different for two positive pulses. How can you get the right impedance result if you don’t have the correct voltages present? Agilent’s method provides differential, common mode, cross terms, all with a single, accurate setup. And this method simplifies the design to allow almost perfect matching of the two positive pulses giving the most accurate results..

29. TDR Customer Presentation, Oct ‘03 Page 29 There are very good reasons why we do what we do…. We use superposition techniques to combine the results of multiple separate measurements “I learned superposition in my first course in electronics. I believe it for circuits with wires and resistors…but I’m not sure about electromagnetics” From the classic text on electromagnetics, “Fields and Waves in Communications Electronics” by Ramo, Whinnery, and Van Duzer, (1965, John Wiley and Sons) we read “It is frequently possible to divide a given field problem into two or more simpler problems, the solution of which can be combined to obtain the desired answer. The validity of this procedure is based on the linearity of the Laplace and Poisson equations. That is  2 (  1 +  2 ) =  2  1 +  2  2 and  2 (k  1 )= k  2  1 The utility of the superposition concept depends on finding the simpler problems with boundary conditions which add to give the original boundary conditions ”. Or…..

30. TDR Customer Presentation, Oct ‘03 Page 30 Don’t worry….it’s covered in the new Application Note! Easy to read and digest TDR is valid only for linear passive devices (or active devices configured as linear and passive). So our technique is completely valid We could have built it with a + and – pulse. Important reasons we did what we did Allows almost perfect symmetry in the stimulus on each leg Asymmetry leads to mode conversion and potentially critical measurement errors 86100 channel steps overlaid – almost exactly the same Linear, passive device to be tested

31. TDR Customer Presentation, Oct ‘03 Page 31 By the way…..the VNA analysis is also based on superposition The VNA can only stimulate one port at a time The VNA uses sinewaves (doesn’t even use pulses!) Precision results obtained by combining results after taking several individual measurements No one ever questions the accuracy of a VNA. “True differential is best” is a myth, and one that is keeping you from making the most accurate measurements.

32. TDR Customer Presentation, Oct ‘03 Page 32 Summary Review of TDR Why Calibration gives superior results Speeding the pulse up significantly for higher resolution Using frequency domain analysis from TDR data to get more insight Why ‘true differential is better’ is a myth that may be keeping you from making the best measurements New literature Application Note: High-precision Time Domain Reflectometry: 5988-9826EN Flyer: 86100 and the Picosecond 4020 lit # 5988-9825EN Accessories Flyer: lit # 5980-2933EN