Emphasis, Equalization & Embedding

Transcription

1 Emphasis, Equalization & Embedding Cleaning the Rusty Channel Gustaaf Sutorius Application Engineer Agilent Technologies Dr. Thomas Kirchner Senior Application Engineer Digital Debug Tools Page 1 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

2 Agenda 1. Introduction 2. Emphasis 3. Equalization 4. Virtual probing by De-Embedding 5. PrecisionProbe Concept 6. Summary Page 2 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

3 3 E s: Signal Conditioning & Measuring TX Channel RX Emphasis: Pre-emphasis De-emphasis Embedding: De-embed path Emulate path Equalization: Passive (Linear Feedforward Eq.) Active (Decision Feedback Eq.)

4 Key measure is eye quality Unequalized 1Gb/s Unequalized 3Gb/s Unequalized 5Gb/s Unequalized 8Gb/s Page 4 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

5 How to clean the rusty channel De-emphasis Equalisation Page 5 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

6 Agenda 1. Introduction 2. Emphasis 3. Equalization 4. Virtual probing by De-Embedding 5. PrecisionProbeConcept 6. Summary Page 6 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

7 Transmitter De-emphasis We can account for loss through the channel at the transmitter with transmitter de-emphasis. De-emphasis is also called preemphasis. The amount of de-emphasis may be programmable. De-emphasis off, measured at receiver De-emphasis on, measured at transmitter De-emphasis on, measured at receiver Page 7 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

8 ExampleDe-Emphasis Channel Input signal Channel Output signal Source: appnote on emphasis Page 8 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

9 De-EmphasiswithN4916A (De-Emphasis Signal Converter) Positive de-emphasis programming start of pulse Negative de-emphasis programming end of pulse Note: de-emphasis is sometimes called also pre-emphasis. Used in standards: PCI Express 1 and 2, SATA 3G b/s, fully buffered DIMM, Hypertransport, CEI 6/11G, 10 GbEthernet. Page 9 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

10 5 Gb/s in out no deemphasis optimized deemphasis With N4916A Page 10 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

11 Agenda 1. Introduction 2. Emphasis 3. Equalization 4. Virtual probing by De-Embedding 5. PrecisionProbe Concept 6. Summary Page 11 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

12 Equalization: Serial Data Equalization N5461A The Serial Data Equalization software is innovative software for the Series that allows for real time equalization of partially or completely closed eyes. Serial Data Equalization provides the following: Modeling of both DFE and FFE Automated tap value creation Basic de-embedding capability Full integration with the Series software Real time updating Equalization wizard Full cursor control to measure eye height The idea behind equalization is to use the voltage levels of the other bits to correct the voltage level of the current bit. Page 12 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

13 FFE Concept an Example Tap the pre-cursors to equalize the bit Bit number: mv 81 mv 182 mv 202 mv -37 mv 160 mv -16 mv -105 mv Equalized signal, e(0) = 16k k k k k 4 105k 5 37k k 7 k i are correction constants called Taps The bits before the bit of interest are called pre-cursors The bits after the bit of interest are called post-cursors Cleaning The Rusty Channel Emphasis, Equalization & Embedding

14 Basic Theory Why Equalization Works The Impulse Response h(t) has all the information contained in a circuit element. Transmission path δ (t) h(t) To get the best taps, we need to invert the process h(t) Equalizer Delay Delay... x x x x e(t) +

15 N5461A Serial Data Equalization Provides a Complete Equalization Wizard and Automated Tap Values 1. Wizard allows for seven real time eye options (including DFE and FFE on a closed eye) 2. Wizard provides full step by step process for clock recovery 3. Wizard provides tap value automation via the FFE and DFE setup menus 4. Wizard makes setting up equalization fast and easy Page 15 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

16 N5461A Equalization Wizard options FFE is applied, but the real time eye is not displayed. You will see only the waveform. 2. No equalization applied. This is to compare an equalized signal versus a nonequalized signal. 3. FFE is applied only to recover the clock, but the referenced eye is unequalized. This is useful forfindingthe recovered clock from a closed eye. 4. Standard FFE equalization. 5. Standard DFE equalization for a non closed eye. 6. Standard DFE equalization for a closed eye. Note the FFE is used to recover the clock, but is notdisplayedin the real time eye. 7. FFE is applied and then DFE is applied to the real time eye. Both are displayed in the resulting realtime eye. Page 16 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

17 N5461A Equalization Wizard options Page 17 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

18 Equalizer demonstration 81134A as ideal source Bad cable or JIM as medium scope as receiver with N5461A equalizer Page 18 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

19 FFE Results taken from the Serial Data Equalization SW Page 19 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

20 Agenda 1. Introduction 2. Emphasis 3. Equalization 4. Virtual probing by De-Embedding 5. PrecisionProbeConcept 6. Summary 7. Addendum: Practical examples Page 20 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

21 De-embedding Fixtures or PCB Traces TP0 TP1 TP2 TP3 TP4 + Tx - EQ Txp Txn Connector Channel Connector Rxp Rxn EQ + Rx - Signal generated here Exits IC here Exits board here Combine measurements and transmission line models to view simulated scope measurements at any location in your design Intuitive GUI speeds setup 21

22 Virtual Probing = Measurement Plane Relocation M What you Have Measurement Plane Connector Fixture Cable Waveform Analyzer Digital Source 50Ω Realtime Oscilloscope= Waveform Analyzer What you Want Digital Source Connector Fixture Cable S Simulated Measurement Plane 50Ω Instrument Termination Page 22 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

23 Removing a Channel Element De-Embedding Compensate for Probing and Fixture Loss Add Margin to Transmitter Characterization TP2 TP1 PCI Express 2, SATA, and Custom Compliance Requirement for Gen 2 Tx Connector Channel Connector Rx PHY PHY TP1 TP2 Page 23 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

24 Agilent De-Embedding Representation: InfiniiSim Example Remove Insertion Loss of 1 Channel Element Page 24 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

25 InfiniiSim: Go as Detailed as you need From 1 block To 9 blocks T= Tx, R = Rx, M = scope, S= Virtual probing point Page 25 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

26 InfiniiSimExample: De-embedding of cable effect Generate 3Gb/s PRBS7 signal Go through 6 meters of cable TX Removal TX Page 26 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

27 InfiniiSim Example: De-Embedding of 6 meter Cable We are going to perform a Transformation of a Waveform ACQUISITION of signal through 6 meters of cable Simulated Result of removing the cable Transfer Function R(t) H(t) = S(t) Page 27 Cleaning The Rusty Channel Emphasis, Equalization & Embedding

28 InfiniiSim Example: De-Embedding DDR2 BGA Probe TRANSIENT S-PARAMETERS Tran Tran1 StopTime=3.0 nsec MaxTimeStep=1.0 nsec SPOutput spoutput1 FileName= FileType=touchstone Format=MA S_Param SP1 Start=50 Mhz Stop=20 GHz Step=0.01 GHz R Term9 R=50 Ohm Vic2_Probe System Aggr_Top Vic2_Bot t VtStep SRC1 Vlow=0 V Vhigh=2 V Delay=.1 nsec Rise=1 psec Term Term1 Num=1 Z=75 Ohm Term Term2 Num=2 Z=75 Ohm Term Term3 Num=3 Z=75 Ohm S2P_Eqn S2P1 S[1,1]=0 S[1,2]=0.01 S[2,1]=sqrt(29050/75) S[2,2]=0 Z[1]=29050 Z[2]=75 DRAM Probe_out Aggr_Bot Aggr_Probe Vic1_Top Vic1_Bot Vic2_Top Vic1_Probe R Term4 R=75 Ohm R Term6 R=75 Ohm W2635_36_RevA1_Model_NoProbe_SUBCKT X1 R Term7 R=75 Ohm R Term8 R=75 Ohm C C1 C=.24 pf R Term5 R=75 Ohm 28 May 28th, 2009

29 Probe at VIA De-embed Probe Probe at BGA InfiniiSim Example: De-Embedding DDR2 BGA Probe RT BGA = 390 ps RT VIA = 183 ps RT De-embed = 175 ps 29 May 28th, 2009

30 Full De-Embedding versus Insertion Loss Removal V Meas (t) TX Channel Element A Channel Element B Channel Element C F u l l D e - E m b e d d i n g VS. TX Channel Element B I n s e r t i o n L o s s R e m o v a l

31 System Model TX A B C S 21Tx S 21A S 21B S S 21C 21Rx S 22Tx = 0 S 11A S 22A S 11B S 22B S 11Rx = 0 S 11C S 22C C o r r e c t A n s w e r S 12A S 12B S 12C TF ABC = S 21A *S 21B *S 21C 1 (S 22A *S 11B + S 22B *S 11C + S 21B *S 11C *S 12B *S 22A )

32 Comparing the two: Insertion Loss Removal I n s e r t i o n L o s s R e m o v a l U s e s e a s y s c o p e m a t h : S 21B -1 TX A B C S 21Tx S 22Tx = 0 S 21A S 21B S 21C S 11A S 22A S 11B S 22B S 11C S 22C S 21B -1 G i v e n A n s w e r TF ABC = S 12A S 12B S 21A *S 21B *S 21C S 21B -1 S 12C Easy Scope Math 1 (S 22A *S 11B + S 22B *S 11C + S 21B *S 11C *S 12B *S 22A ) I n t e r a c t i o n A r t i f a c t s A r e S t i l l T h e r e!!!

33 Comparing the two: true removal of block B F u l l D e - E m b e d B TX A C S 21Tx S 21A S 21C S 21Rx S 21C S S 11A S 22A S 11C S 22C 22Tx = 0 S 11Rx = 0 S 12A S 12C C o r r e c t A n s w e r TF AC = S 21A *S 21C 1 (S22A*S11C)

34 Comparing the two: Full De-embed F u l l D e - E m b e d u s e s c o m p l e x s c o p e m a t h t h a t r e m o v e s a l s o i n t e r a c t i o n a r t i f a c t s ( i n t h i s c a s e b e t w e e n A - B a n d B - C a n d A - B - C ) : F u l l D e - E m b e d As measured TX S 21Tx S 22Tx = 0 A B C S 21A S 21B S 21C S 11A S 22A S 11B S 22B S 11C S 22C Complex Function Scope Math S 12A S 12B S 12C TF AC = S 21A *S 21B *S 21C [1 (S 22A *S 11B + S 22B *S 11C + S 21B *S 11C *S 12B *S 22A )] S 21B -1 [1 (S 22A *S 11B + S 22B *S 11C + S 21B *S 11C *S 12B *S 22A )] [1 (S 22A *S 11C )] I n t e r a c t i o n A r t i f a c t s A r e R e m o v e d!!!

35 DEMO InfiniiSim Virtual Probing Test Fixture to De-Embed Page 35

36 DEMO JIM & INFINIISIM 81134A/ Setup at Amstelveen Office Infiniisim OFF Infiniisim ON Page 36

37 Agenda 1. Introduction 2. Emphasis 3. Equalization 4. Virtual probing by De-Embedding 5. PrecisionProbe Concept 6. Summary 7. Addendum: Practical examples Page 37

38 Changing scopes into VNA s using PrecisionProbe (N2809A) Characterize and correct any input path to your oscilloscope input using only your oscilloscope

39 The problem: a real life example Customers challenge: To characterize and correctly identify every path in this switch system. Then to remove any insertion loss from the path to maximize margins Fix #1: Use a VNA/TDR to characterize all paths, correctly identify each, and use InfiniiSim to remove the loss Fix #2: PrecisionProbe! Customer currently uses PrecisionProbe to characterize and compensate for all 112 input paths resulting time savings and margin gains with every measurement Recently a customer gained 15% in their margins by using PrecisionProbe, they now pass their PCIE gen3 testing

40 The Solution: PrecisionProbe PrecisionProbe Quickly and Easily: - Characterizes and corrects the frequency response (VOut/VIn) magnitude and phase of any probe and probe head combination - Characterizes and corrects for insertion loss caused by cables and fixtures - Characterizes and corrects for insertion loss caused by switches for probes and cables.

41 PrecisionCable characterizes and corrects in three easy steps 1. Measure baseline 2. Measure loss due to cable 3. Save File Page 41

42 How it works Agilent s X- Series uses its world class 200 GHz Indium Phosphide technology to provide a <15ps edge to the oscilloscope Comparing the baseline measurement with the cables influence, proper characterization is done and corrections can be made Infiniium s custom InP calibration edge Fast edge or Baseline Calibration edge is then measured by the X-Series Edge with lossy cable Lossy cable is then measured agai inst the fast edge e

43 Cable characterized with PrecisionProbe Applied corrected filter Response of cable with no correction Corrected cable response

44 Cable correction results Before PrecisionProbe After PrecisionProbe S21 cable loss is removed through compensation Rise Time improves from 67 ps to 21 ps!

45 The real time eye Results: More margins! 20% less jitter 33% more eye height Slightly wider eye

46 Why using PrecisionProbe for characterizing probes Issues that make the problem worse 1. Cables and channels are lossy 2. Switch paths can all vary 3. Probe characteristics are different from probe to probe 4. Custom probes have no oscilloscope correction 5. Tip and probe head correction is typically based on a model and does not represent the exact physical probe 6. Oscilloscope vendors use different frequency response correction methods to account for probing Uncorrected

47 Probes: PrecisionProbe is the solution Transfer function of probe with no correction Corrected VOut Uncorrected VOut

48 Connections for Probe Calibration Vsrc The signal at the probe point before the probe is connected which would be the signal at the probe point if an ideal probe with infinite input impedance were connected VIn The signal at the probe point while the signal is being loaded by the probe. Probe loading is caused by the input impedance of the probe making a voltage divider with the source impedance of the circuit being measured. VIn VOut The signal that is output from the probe Souce impedance The impedance of the circuit that is driving the probe, which is the impedance looking back input the point being probed with the probe connected VOut VIn (probe) X-series CAL output VIn (to scope) X-series CAL output (step)

49 Probes: final results Transfer function of probe with no correction Corrected VOut Uncorrected VOut 1. PrecisionProbe corrects VOut is directly on top of VIn indicating a corrected VOut/VIn transfer function 2. Transfer function is now flat for the entire bandwdith of the probe 3. 6dB of loss is now compensated

50 Comparison PrecisionProbe vs VNA Figures show a solder in probe characterized by Figures show a solder in probe characterized by PrecisionProbe and a VNA. Notice how closely the characterization matches both systems

51 Summary: PrecisionProbe helps with the following: 1. Cables and channels are lossy 2. Probe characteristics are different from probe to probe 3. Switch paths can all vary 4. Custom probes have no oscilloscope correction 5. Tip and probe head correction is typically based off a model and does not represent the exact physical probe 6. Oscilloscope vendors use different frequency response correction methods to account for probing Uncorrected Corrected By using PrecisionProbe you will further increase your margins without adding significant time or extra equipment

52 Agenda 1. Introduction 2. Emphasis 3. Equalization 4. Virtual probing by De-Embedding 5. PrecisionProbe Concept 6. Summary Page 52

53 Pag Questions?