Ensuring Signal and Power Integrity for High-Speed Digital Systems

Transcription

1 Ensuring Signal and Power Integrity for High-Speed Digital Systems An EMC Perspective Christian Schuster Institut für Theoretische Elektrotechnik Technische Universität Hamburg-Harburg (TUHH) Invited Presentation at the IEEE International Conference on Consumer Electronics (ICCE), Berlin, September 6-9, 2015

2 Abstract With increasing data rates and reduced margin for communication errors both consumer electronic products as well a large-scale digital systems like data centers have to be designed very carefully with respect to their electrical integrity. In this presentation two aspects of this integrity, namely signal integrity (SI) and power integrity (PI), will be explained in some detail. The focus will be put mostly on packaging and electromagnetic compatibility (EMC) aspects. Topics that will be addressed include discontinuities, transmission line effects, crosstalk, bypassing and decoupling, via and power plane effects, return current issues, and measurement techniques. The presentation should be suitable for both a technical and a non-technical audience. For more information on SI and PI research at TUHH visit: C. Schuster, TUHH 2

3 Outline (1) Motivation (2) SI, PI & EMI (3) High-Speed Digital Systems (4) Improving SI (5) Improving PI (6) Wrapping Up C. Schuster, TUHH 3

4 (1) Motivation C. Schuster, TUHH 4

5 Digital Link Data Rates Data Rate [Gb/s] 10 Infiniband 10.0 DDR G Ethernet PCIe 5.0 Hyper Transport 5.2 SATA III 6.0 SA-SCSI 3.0 Fibre Channel 4.25 DVI 3.7 USB FireWire up 3.2 CPU to CPU Storage Network/ Peripherals C. Schuster, TUHH 5

6 Digital Link Frequency Trends C. Schuster, TUHH 6

7 (2) SI, PI & EMI C. Schuster, TUHH 7

8 Digital Link Seen From.. Driver Via PCB Power Plane Ground Plane DC Power Supply Receiver C. Schuster, TUHH 8

9 .. a Signal Transmission Perspective Signal Transmission Issues: Attenuation, Reflection, Dispersion, Interference, Crosstalk C. Schuster, TUHH 9

10 .. a Signal Transmission Perspective Signal Transmission Issues: Attenuation, Reflection, Dispersion, Interference, Crosstalk C. Schuster, TUHH 10

11 .. a Power Delivery Perspective Power Delivery Issues: Voltage Drop, Switching Noise, Crosstalk C. Schuster, TUHH 11

12 .. a Power Delivery Perspective Power Delivery Issues: Voltage Drop, Switching Noise, Crosstalk C. Schuster, TUHH 12

13 .. an EMI Perspective Electromagnetic Interference Issues: Near Field Coupling, Radiated Emissions C. Schuster, TUHH 13

14 .. an EMI Perspective Electromagnetic Interference Issues: Near Field Coupling, Radiated Emissions C. Schuster, TUHH 14

15 SI + PI + EMI = Comprehensive EMC Elements of a comprehensive EMC C. Schuster, TUHH 15

16 SI/PI Foundations and Resources Circuit Design & Simulation Antenna Theory Communication Theory Numerical Techniques HF Measurement Techniques Coupler & Filter Design Transmission Line Theory SI / PI EM Field Theory Electromagnetic Compatibility Network Theory CAD Tools System Theory Material Characterizationj C. Schuster, TUHH 16

17 SI/PI Foundations and Resources C. Schuster, TUHH C. Schuster, TUHH 17 Figures C. Schuster, TET, TUHH

18 SI/PI in the IEEE Community Number of publications found in IEEE Xplore containing the index terms: Signal Integrity Power Integrity C. Schuster, TUHH 18

19 SI/PI in the EMC Community C. Schuster, TUHH 19

20 SI/PI in the EMC Community C. Schuster, TUHH 20

21 (3) High-Speed Digital Systems C. Schuster, TUHH 21

22 Daughtercard A High-Speed Digital System Housing / Chassis Cable IC (Transmitter) Package / Module Connector IC (Receiver) Connector Socket Backplane / Motherboard C. Schuster, TUHH 22

23 The SI Challenge Interconnect (Link) Connector C. Schuster, TUHH 23

24 Effect of Interconnects The ideal interconnect will simply delay the signal: Tx Rx Any real interconnect will additionally change timing and amplitude: t Tx Rx t C. Schuster, TUHH 24

25 Jitter and Noise The deviations in timing and amplitude are in general called: t Timing jitter or simply: JITTER Amplitude noise or simply: NOISE C. Schuster, TUHH 25

26 Jitter and Noise In the eye diagram timing jitter and anplitude noise are defined as follows: NOISE JITTER Receiver Sampling Point C. Schuster, TUHH 26

27 The PI Challenge 1 V 3.3 V VRM Connector C. Schuster, TUHH 27

28 Effect of Common Power Delivery Z PDN IC #1 IC #2 U 0 PDN = Power Delivery Network C. Schuster, TUHH 28

29 Effect of Common Power Delivery R L u IC U 0 Du i Gate1, i Gate2, u IC = U 0 - Du d Du( t) R Gate1 Gate1 Gate1 Gate1 dt i ( t) i ( t)... L i ( t) i ( t)... "DC-drop or IR-drop" "DI-drop or DI-noise" C. Schuster, TUHH 29

30 (4) Improving SI C. Schuster, TUHH 30

31 Improving Signal Integrity 1. Match terminations 2. Minimize discontinuities 3. Reduce Coupling 4. Limit attenuation 5. Balance deficiencies C. Schuster, TUHH 31

32 Typical Digital Link Design Data.. Interconnect Equalizer + Slicer.. Data.. Equalizer Serializer CDR Deserializer Tx Clock Clock & Data Recovery Rx High performance digital links are mostly serial: HSS = HIGH SPEED SERIAL. The technology is typically CMOS with the links being voltage mode, unidirectional, serial, point-to-point, and source-synchronous. Both single-ended and differential signaling can be found. For improved bandwidth equalization is typically used in the Tx, Rx, or both. C. Schuster, TUHH 32

33 Improving Signal Integrity 1. Match terminations 2. Minimize discontinuities 3. Reduce Coupling 4. Limit attenuation 5. Balance deficiencies C. Schuster, TUHH 33

34 Effect of Terminations Let s use the following interconnect (link) model: Z 0,, l Z S Z L?? u 0 u 1 u 2 Transmitter Interconnect Receiver C. Schuster, TUHH 34

35 Transmission Lines in Digital Systems Microstrip Line Z r ln 5.98h 0.8 w t (h = height of dielectric, w = conductor width, t = conductor thickness) Stripline (symmetric) Z 0 60 r ln 1.9 h 0.8 w t (h = height of dielectric, w = conductor width, t = conductor thickness) Metal Dielectric C. Schuster, TUHH 35

36 Effect of Terminations Let s use the following interconnect (link) model: Z 0,, l Z S Z L?? u 0 u 1 u 2 u u 2 const. and max.! 0 C. Schuster, TUHH 36

37 Effect of Terminations Z 0,, l Z S Z L input acceptance source transmission source reflection TL transfer function load transmission load reflection C. Schuster, TUHH 37

38 C. Schuster, TUHH 38 l Z,, 0 Z L Z S Effect of Terminations!! 1 ) (1 1 S L 2 L S L 2 L 0 trans 0 2 r r H r H a r r H t H a u u u u

39 Effect of Terminations Z 0,, l Z S Z L Z L Z 0 u u 2 0 a H Z S Z L Z 0 u u H C. Schuster, TUHH 39

40 Voltage Voltage Matched interconnect: Effect of Terminations lossless transmisson line lossy transmisson line Time Mismatched Interconnect: T D low source impedance 2T D high source impedance Time C. Schuster, TUHH 40

41 Effect of Terminations 1 Z S 10Ω, Z 0 50Ω, Z L 1kΩ zero losses 2 Z S 50Ω, Z 0 50Ω, Z L 100Ω zero losses 1 3 Z S 50Ω, Z 0 50Ω, Z L 50Ω zero losses Z S 100Ω, Z 0 50Ω, Z L 100Ω zero losses Z S 10Ω, Z 0 50Ω, Z L non-zero losses 1kΩ 6 Z S 50Ω, Z 0 50Ω, Z L 50Ω non-zero losses (all lines have a delay of 0.1 ns) C. Schuster, TUHH 41

42 Improving Signal Integrity 1. Match terminations 2. Minimize discontinuities 3. Reduce coupling 4. Limit attenuation 5. Balance deficiencies C. Schuster, TUHH 42

43 Packaging of Digital Systems Interconnect (Link) Connector C. Schuster, TUHH 43

44 Effect of Lumped Discontinuities Signal In C. Schuster, TUHH Signal Out Source Voltage u 1 50 u nh 2 Received Voltage Tx-Output Bond Wire Rx-Input C. Schuster, TUHH 44

45 Effect of Lumped Discontinuities u 2 (t) / u 1 (t) Attenuation of high frequency signal components Slowing down" of the edges of a digital signal Frequency Response Step Response Magnitude of u 2 / u 1 f GHz t 1/w 0 = 25 ps Frequency [GHz] Time [ps] C. Schuster, TUHH 45

46 Effect of Lumped Discontinuities Signal In Signal Out Y. Kwark, IBM Source Voltage 50 u 1 1 pf 50 u 2 Received Voltage Tx-Output Via Rx-Input C. Schuster, TUHH 46

47 Effect of Lumped Discontinuities Attenuation of high frequency signal components!! u 2 (t) / u 1 (t) Slowing down" of the edges of a digital signal!! Frequency Response Step Response Magnitude of u 2 / u 1 f GHz t 1/w 0 = 25 ps Frequency [GHz] Time [ps] C. Schuster, TUHH 47

48 Effect of Distributed Discontinuities Z 0 Z,,l Z 0 1 inch, 45 Ohm mismatched transmission line at c 0 /2 c f GHz 4l Frequency Response (Scattering Parameters) C. Schuster, TUHH 48

49 300fF 300fF 300fF 300fF Overall Effect of Discontinuities Port1 Port2 2nH Z=49 P=1cm Z=48 P=15cm 2nH Z=52 P=5cm Z=48 P=1cm 2nH C. Schuster, TUHH 49

50 Improving Signal Integrity 1. Match terminations 2. Minimize discontinuities 3. Reduce coupling 4. Limit attenuation 5. Balance deficiencies C. Schuster, TUHH 50

51 Packaging of Digital Systems Interconnect (Link) Connector C. Schuster, TUHH 51

52 Effect of Coupling Consider two transmission lines in close proximity: (1) Input Aggressor Line (Active Line) (2) Output (3) Near End Victim Line (Quiet Line) (4) Far End C. Schuster, TUHH 52

53 Effect of Coupling Consider two transmission lines in close proximity: I C I C-NE I C-FE Capacitive Crosstalk C. Schuster, TUHH 53

54 Effect of Coupling Consider two transmission lines in close proximity: U L U L-NE U L-FE Inductive Crosstalk C. Schuster, TUHH 54

55 Effect of Coupling Consider two transmission lines in close proximity: (1) Input (2) Output I C (3) Near End (4) Far End U L NEXT = Near End Crosstalk (sum of ind. and cap. crosstalk) FEXT = Far End Crosstalk (difference of ind. and cap. crosstalk) C. Schuster, TUHH 55

56 Improving Signal Integrity 1. Match terminations 2. Minimize discontinuities 3. Reduce Coupling 4. Limit attenuation 5. Balance deficiencies C. Schuster, TUHH 56

57 Contributors to Line Losses Attenuation usually increases with frequency. The exact calculation can be difficult but for weakly lossy lines: R wl and G wc a convenient approximations exists: a R 2 C L G 2 L C a c a d with a c = attenuation due to conductor losses and a d = attenuation due to dielectric losses. The following dependencies are often found: R ~ w /k G ~ wctand with k = electrical conductivity and tan d = loss tangent. C. Schuster, TUHH 57

58 Time Domain Effect of Losses When taking into account DC losses the effect in the time domain is twofold: edge degradation DC drop Voltage step response without losses step response with losses Time C. Schuster, TUHH 58

59 Frequency Dependence of Losses For the frequency dependence follows with these assumptions: H e l e al e a l c e a l d ~ e const c f e const d f ln H ~ const c f const d f In other words, a typical semilogarithmic plot of the magnitude of the transfer function will be dominated by a square root behavior at lower and a linear behavior at higher frequencies. square root linear total C. Schuster, TUHH 59

60 Dielectric Packaging Materials Dielectric materials are typically classified with respect to their relatice dielectric constant r and their loss tangent tan d: "FR-4" tan d Teflon (PTFE) Silicon Quartz (SiO 2 ) Alumina (Al 2 O 3 ) r C. Schuster, TUHH 60

61 Improving Signal Integrity 1. Match terminations 2. Minimize discontinuities 3. Reduce coupling 4. Limit attenuation 5. Balance deficiencies C. Schuster, TUHH 61

62 Overview of Equalization Techniques Data.. Interconnect Equalizer + Slicer.. Data.. Equalizer Serializer CDR Deserializer Tx Clock Clock & Data Recovery Rx Most high speed serial links nowadays use some EQUALIZATION, i.e. some kind of signal processing technique to correct for the degradations in the interconnect, and thereby improve the quality of signals. When the corrections are applied at the transmitter equalization is sometimes also called DE- EMPHASIS or PRE-EMPHASIS. Apart from continuous time equalization (CTE) signal processing takes place in the discrete time domain / digital filters. C. Schuster, TUHH 62

63 Overview of Equalization Techniques Interconnect Equalization Equalized Response TF = f f f In frequency domain the effect of equalization can be to some extent be visualized as the flattening of the transfer function of the interconnect. An interconncet with a completely flat transfer function would transmit a signal undisturbed apart from a potential amplitude scaling. C. Schuster, TUHH 63

64 Overview of Equalization Techniques Two big classes of (digital, discrete) equalization exist: Equalization Linear Feedforward Equalization (LFE/FFE) - Uses only information from the current and previously received bits - Can be interpreted as a nonrecursive digital filter (finite impulse response filter) Distributed Feedback Equalization (DFE) - Uses a feedback loop after the signal has been decoded by an LFE/FFE - The output of the LFE/FFE is added to the feedback loop resulting in the equalized signal C. Schuster, TUHH 64

65 (5) Improving PI C. Schuster, TUHH 65

66 Improving Power Integrity 1. Decrease PDN impedance 2. Add decoupling 3. Add more decoupling 4. Use several power supplies 5. Use on-chip VRMs C. Schuster, TUHH 66

67 PDN Elements High Power DC Supply Discrete Decoupling Capacitors (various sizes) IC incl. Power/Ground Grid & Integrated Decaps Package incl. Power/Ground Planes Voltage Regulator Module Printed Circuit Board incl. Power/Ground Planes C. Schuster, TUHH 67

68 Improving Power Integrity 1. Decrease PDN impedance 2. Add decoupling 3. Add more decoupling 4. Use several power supplies 5. Use on-chip VRMs C. Schuster, TUHH 68

69 PDN Impedance A typical maximum ripple for ditigal systems is: Du u max 0 maximum ripple 5% to10% With a 10% value the following numbers can be obtained for applications of the early 1990'ies: of 2000 and on: u 0 Z i / i P u 0 avg avg avg Target 5.0 1A W V Ω 0.5Ω u 0 Z i / i P u 0 avg avg avg Target 1.2 V 120A 0.01 Ω 144 W 0.001Ω = 1 m! C. Schuster, TUHH 69

70 Improving Power Integrity 1. Decrease PDN impedance 2. Add decoupling 3. Add more decoupling 4. Use several power supplies 5. Use on-chip VRMs C. Schuster, TUHH 70

71 Low Frequency Equivalent PDN Circuit R L U 0 ~ Z IC ( f ) C. Schuster, TUHH 71

72 Low Frequency Equivalent PDN Circuit including a "decoupling" or "bypass" capacitor: R L U 0 ~ Z IC ( f ) C some nf to some mf C. Schuster, TUHH C. Schuster, TUHH 72

73 Heuristic explanation: Decoupling Effect R L U 0 ~ Z IC ( f ) C Frequency domain: Beyond the resonance frequency the capacitor decouples the part of the PDN that lies "left" of him, i.e. the IC sees only the impedance of the capacitor. Time domain: The capacitor stores charges close to the IC that can become currents needed for fast switching. It is like a "small battery". C. Schuster, TUHH 73

74 Real Word Decoupling Capacitors Unfortunately, there is no ideal capacitor available in the real world! Ideal world: and real world: C R L C R is also is called the EQUIVALENT SERIES RESISTANCE (ESR) and L the EQUIVALENT SERIES INDUCTANCE (ESL). As a consequence any real world capacitor behaves approximately like an inductor beyond its resonance frequency: w 0 1/ LC C. Schuster, TUHH 74

75 Improving Power Integrity 1. Decrease PDN impedance 2. Add decoupling 3. Add more decoupling 4. Use several power supplies 5. Use on-chip VRMs C. Schuster, TUHH 75

76 More Decoupling ~ board-level package-level chip-level Amount of charge, size of decoupling capacitance Speed of charge delivery, effective frequency C. Schuster, TUHH 76

77 PDN Impedance More Decoupling ~ board-level package-level chip-level Inductance of VRM Capacitance of Bulk Decaps ESL of Decaps, Pads and Vias Capacitance of P/G Planes & Small Decaps ESL of Planes and Inductance of Package Capacitance of Decaps on Package and IC Remaining On.Chip Inductance Target Impedance 1 MHz 500 MHz 1 GHz 10 GHz C. Schuster, TUHH 77

78 C. Schuster, TUHH 78 0,1,2,...), ( r r 0 n m b n a m c f mn Resonance frequencies of power/ground plane pairs: Examples of standing wave patterns on a rectangular power/ground plane pair. Power/Ground Plane Resoances

79 (6) Wrapping Up C. Schuster, TUHH 79

80 Comprehenisve EMC of Digital Systems The basic goals of SI, PI, and EMI control for a digital system are complementary to each other. SIGNAL INTEGRITY: insure acceptable quality of signals within SNR Target System Frequency POWER INTEGRITY: insure acceptable quality of power delivery within PDN Impedance Target Frequency System EMI: insure acceptable level of interference with the outside EMI Target System Frequency C. Schuster, TUHH 80