Microwave Measurements for signal integrity applications

Transcription

1 Microwave Measurements for signal integrity applications Prof. Andrea Ferrero,FIEEE Distinguished Microwave Lectures Dip. Elettronica- Politecnico di Torino

2 Summary Signal Integrity and Microwave S-parameter: so what? VNA Hardware Evolution Error Models and Calibration Techniques Interconnection and Fixture Design Calibration design for the DUT Uncertainty

3 Signal Integrity and Microwave

4 00 Introduction Dual-channel 0Gbps per port Bi-directional Dual-protocol (PCI Express and DisplayPort) Compatible with existing DisplayPort devices Daisy-chained devices Electrical or optical cables Low latency with highly accurate time synchronization Uses native protocol software drivers Power over cable for bus-powered devices

5 The S-matrix of a transmission line a a b Z Z R b l Port Port z s b a b s b Sa b s a 0 0, s b a a 0 e s s jkl a a, s b b b a a 0 s s e a a jkl s s, s a a b a a 0 0 S 0 e jkl e 0 jkl So to completely describe the propagation along a trasmission line we will need: REFERENCE PLANES REFERENCE IMPEDANCE S-MATRIX

6 Differential S-parameters? The differential mode Ed propagates mainly in the air thus it suffers much less of dielectric loss and anysotrtopy FR4 is a must for Digital application but FR4 is lossy and anysotropic thus Differental propagation became a must for high speed digital systems

7 Differential S-parameters What if instead of single ended voltages and currents we wish to use differential ones and associate the information to a couple of wires? I I 3 For Each Couple V V I V 3 I 4 V 4 V djk V cjk I djk I cjk V V j k ( V V )/ j k ( I I )/ j k ( I I ) j k 7

8 Differential S-parameters What are the propagation properties and is it usefull to have an S-parameter equivalent? Use a linear combination of V and I it s just another convention but to link it to propagation became more tricky: Which Reference impedance we need to take? What if we wish to have some port left single ended, i.e. an Operational Amplifier? Which are the properties of the new parameters? 8

9 Mixed Mode S-parameter Traditional definitions are: a b a b djk djk cjk cjk ( a ( b ( a ( b S j j j j a b a b k k k k ) ) ) ) BUT THESE ARE VALID ONLY IF Z Z cjk djk R Real Only R Real Only MSM 9

10 Generalized Mixed Mode S-parameters In general we may have a b a b djk djk cjk cjk R R R R djk djk cjk cjk V V V V djk djk cjk cjk Z Z Z I I I I Z djk djk djk djk cjk cjk cjk cjk Z Z Z Z djk djk cjk cjk p d ifferen tial p orts I d V d I c V c I d(p-)p V d(p-)p I c(p-)p V c(p-)p I V I V I p- V p- I p V p Ip+ n-ports V p+ S ( Ξ Ξ S)( Ξ Ξ S) BILINEAR MATRIX TRANSFORM n -p sing le end ed p orts In Vn 0

11 An example: The OpAmp ASSUME R R R D C OUT R0 R / 0 R 0

12 port Measurements ,,, a a a a a b s a b s a b s a b s a a s s s s b b Sa b S S a b a b

13 The old questions of S-parameter Measurements How can we generate microwave signals? How can we sample microwave signals? Where s the reference plane? What s the reference impedance?

14 Plus new problems for digital Low cost application How do I keep reasonable microwave signals on non microwave substrate? How can I make proper interconnections to measure these signals? How much accuracy can I accept?

15 VNA BASIC SCHEME IF Digitizer FOUR-CHANNEL MICROWAVE RECEIVER a m b m b m a m DUT PORT PORT BIAS BIAS REFLECTOMETER SIGNAL SEPARATION MICROWAVE SOURCE 5

16 From ports to multiports 4 Ports 4 Ref 4 Rec -ports Ref Rec 6

17 ports VNA Ref Switched Rec LEFT PORTS RIGHT PORTS 7

18 ports VNA Ref Switched Rec LEFT PORTS RIGHT PORTS

19 Interfacing Repeatibility Custom Fixtures Standard Availability

20 On Wafer

21 Let s summarize up to now. Directional Couplers have finite directivity and frequency depend behaviour. Switches are not ideal and frequency dependent 3. Reference Plane position depends on cable, adapter interconnections and so on 4. DownConversion and Digitizing problems like:. Source Phase Noise. Frequency accuracy and repeatibility 3. Non linearity of mixer/sampler 4. ADC Dynamic Range & Speed

22 Cause of Uncertainty Systematic Errors (85%) Microwave Components Interconnections Incorrect Standard Modeling Calibration Algorithm Random Error (0%) Connection Repeatibility Frequency Stability Noise Drift (5%)

23 Is Calibration fundamental? What if we would measure 30g of Ham with the scale plate of ton? THIS IS THE SAME EFFECT OF m cable at 0GHz if we are looking for degree of phase shift on S

24 Raw vs. Corrected Data

25 How does the calibration work? An error model A Specific Algorithm A Standard Sequence

26 Coax TRL On-Board Calibration Structures Thru and Line Structures Reflect and Match Structures 6

27 Multiport VNA Calibration Multiport standard may be required Calibration Algorithm must be found Cannot be a simple extension of the port ones

28 Multiport Calibration We do not have multiport standards We may not have Thrus We cannot connect one port to any others

29 Multiport VNA -state A: two side ports State A: port on the left, port on the right 4 directional couplers for the ports as the standard ports VNA LEFT PORTS RIGHT PORTS

30 Multiport VNA -state B: one side two ports State B: ports on the same side 3 directional couplers for the ports as the standard 3 sampler VNA each port is alternatively terminated LEFT PORTS RIGHT PORTS

31 Two States Multiport Error Model The partial reflectometer multiport system has two states, for each port: Linear Receivers Linear Network DUT STATE A STATE B

32 The multiport cal equation And the de-embedding is: 6n - unknowns Based on S parameters Always defined for any standards Can be used to find H,L,M,K,F,G during the cal As well as to find dut S matrix during the measurement A Novel Calibration Algorithm for a Special Class of Multiport Vector Network Analyzers,Ferrero, A.; Teppati, V.; Garelli, M.; Neri, A. IEEE Transactions on Microwave Theory and Techniques, Volume 56, Issue 3, March 008 3

33 Dynamic Calibration Since no constrains are given on the standard type and the math can combine whatever sequence, the calibration becomes dynamic i.e. the software can generate the standard sequence which gives a set of enough linear independent equations as well as it accomplished for: Connectors at each ports Available standards USE ONLY or ports ONES!! User interconnection description Use of particular two port pairs self calibration 33

34 An Example a Socket Measurement

35 8-ports Socket Setup

36 Let s Design the Cal P LRM P5 P P3 P4 Thru Thru Thru P6 P7 P8

37 8-Port LRM Calibration Matrix Port Port Port 3 Port 4 Port 5 Port 6 Port 7 Port 8 Port X X X X P_LRM X X X Port X X X X Thru Thru X X Port 3 X X X X X Thru Thru X Port 4 X X X X X X Thru Thru Port 5 P_LRM Thru X X X X X X Port 6 X Thru Thru X X X X X Port 7 X X Thru Thru X X X X Port 8 X X X Thru X X X X Calibration Procedure: Thru Port, 5 Thru Port, 6 Thru Port 3, 7 Thru Port 4, 8 Thru Port, 5 Thru Port 3, 6 Thru Port 4, 7 Reflect Port Reflect Port 5 Load Port Load Port 5 Structure (All ports touchdown) Structure (All ports touchdown) Structures 3 4

38 GND SIG TERM Probe Touchdown 8-Port LRM Probe Touchdown N/A 8 Probe Touchdown Probe Touchdown 4 N/A N/A N/A 8

39 Calibration Design: A better cal with no xtalk P LSM P5 P Rec LSM P6 P3 LSM Rec P7 P4 Rec LSM P8

40 8-Port LRM/LSM Multi-Calibration Matrix with Reciprocal Thrus Port Port Port 3 Port 4 Port 5 Port 6 Port 7 Port 8 Port X Recip X X P_LSM X X X Port Recip X X X X P_LSM X X Port 3 X X X Recip X X P_LSM X Port 4 X X Recip X X X X P_LSM Port 5 P_LSM X X X X X X X Port 6 X P_LSM X X X X Recip X Port 7 X X P_LSM X X Recip X X Port 8 X X X P_LSM X X X X Calibration Procedure: 4 separate -port LSM/LRM calibrations linked with Thru Port, 5 reciprocal thru standards Thru Port, 6 Structure Thru Port 3, 7 No wasted probe touchdowns Thru Port 4, 8 Never move probe tips in x or y direction Recip, Recip 3, 4 Structure Full characterization of every port Recip 6, 7 Reflect Port, Reflect Port 5 Could provide more accurate calibrations Reflect Port, Reflect Port 6 Structures 3 Reflect Port 3, Reflect Port 7 Reflect Port 4, Reflect Port 8 Load Port, Load Port 5 Load Port, Load Port 6 Load Port 3, Load Port 7 Structures 4 Load Port 4, Load Port 8

41 8-Port LRM/LSM Standards (Probe tip Calibration) Probe Touchdown 5 Probe Touchdown X Length Probe Touchdown X Length Probe Touchdown Minimize probe tip Xtalk GND SIG TERM

42 Socket/Board Setup Close-up On Socket PROBES Land Places Cal Standards On Board PROBES Land Places

43 Socket-Board Data SDD-SDD-SDD33-SDD44

44 Socket-Board Data SDD - SDD34

45 Socket-Board Data SD4 SD3 (Far End Xtalk)

46 Socket-Board Data SD3 SD4 (Near End Xtalk) Bottom Board Top Board

47 Accuracy FAQ What s the residual error after the calibration? What s the overall accuracy of my measurements? What can I do to check if my calibration is good or bad? 47

48 General Uncertainty Procedure Calibration Measurement

49 S matrix Uncertainty We need the full covariance matrix, because we want the possibility to compute the mixed mode parameters, so:??

50 Where the Uncertainty comes from Standard Models Measurement Noise Repeatability

51 Repeatability Model

52 .4mm and the cable effect on repeatability

53 Conclusion VNA Hw is today capable of high accurate and fast measurements. Modern Calibration Technology solves many issues in multiport structure S parameter measurements Proper design of the measurement bench dramatically improves data accuracy Modern Software are today available to handle the measurement complexity and compute the uncertainty 53

54 Acknoledgements Valeria Teppati, Serena Bonino Politecnico of Torino Marco Garelli HFE Brett Grossmann, Tom Ruttan, Evan Fledell Intel Corp Jon Martens Anritsu Corp Dave Blackham Agilent