signal integrity - a crash course [r lott]

Signal Integrity: A Crash Course!

Presenter: Ryan Lott

Signal Integrity & Microwave Measurements Engineer

Arkansas Signal Integrity Community (ASIC) [email protected]

1

Scope

• Basic Introduction

– Typical Interconnects & Their Properties

– Organizational Groups & Standards

– Frequency & Time Domain Characterization

– S-Parameters & VNA Introduction

– Recommended Learning Materials

Best of all… completely free and unbiased!

2

About Me

• Texas A&M BSEE

– Graduated Dec 2013

• Worked at Molex (Maumelle, AR)

– Jan 2014 – Feb 2016

• Now working at Spectra7 Microsystems Ltd. in Little Rock, AR.

• Fell in love with SI along the way and started the Arkansas Signal Integrity Community.

3

What is Signal Integrity?

• Basic Definition:

– Can I get my signal from point A to point B and still read the read the signal?!

4

Lecture Primer – Maxwell’s Equations

5

Lecture Primer – Maxwell’s Heaviside’s Equations

6

Lecture Primer – Maxwell’s & Heaviside’s Equations

7

Words of Wisdom…

There is no such thing as “luck” in high speed

design.

8

Words of Wisdom…

“A Good answer now is better than great answer late.”

-Eric Bogatin

9

Words of Wisdom…

Study!

Find the Root Cause!

Execute!

10

My Learning Philosophy

• There are three ways to success in SI industry

– 1) Experience Only

– 2) Academia Only

– 3) Combine (1) & (2)!

• Option (3) will push you to the limit and accelerate you through the learning curve.

• Rate of learning is proportional to the number of measurements and experiments you make, virtual and/or real! Get to work!

11

Where Does SI Apply?

• PCB Design • Connector Design • Cable Design • Computer HW Design • Chip Design • _______ Design

Practically EVERYWHERE

12

The “Physical Layer”

“Driver” “Receiver”

Insert Interconnect(s) Here!

“The Data Path”

Can I get my signal from point A to point B and still read the signal?!

1

2

3

Types of Interconnects: • Drivers • Receivers • PCB/Backplanes • Cables • Optical Fiber • Connectors • Chip Package • Chip IC Lanes

Types of SI Problems: • Loss • Reflections/Terminations • Radiated Emissions • Skin-Effect • Stubs • Skew • Surface Roughness • XTALK (“CrossTalk”)

MORE Types of SI Problems: • Ringing • Jitter • Return Path Discontinuity • Dispersion • Mode Conversion • Vias • Proximity Effect • BER (Bit-Error-Rate)

Many issues for such a simple idea... 13

The “Physical Layer”

“Driver” “Receiver”

Insert Interconnect(s) Here!

“The Data Path”

Can I get my signal from point A to point B and still read the signal?!

1

2

3

Types of Interconnects: • Drivers • Receivers • PCB/Backplanes • Cables • Optical Fiber • Connectors • Chip Package • Chip IC Lanes

Types of SI Problems: • Loss • Reflections/Terminations • Radiated Emissions • Skin-Effect • Stubs • Skew • Surface Roughness • XTALK (“CrossTalk”)

MORE Types of SI Problems: • Ringing • Jitter • Return Path Discontinuity • Dispersion • Mode Conversion • Vias • Proximity Effect • BER (Bit-Error-Rate)

Many issues for such a simple idea... 14

Break Up The System

• For systems to work, usually the parts of the system/channel (Chip,PCB/Backplane,Cable,…) are split up in the industry and, at first, designed separately. – Spectra7/Molex/Amphenol/FCI/TycoElectronics/Samtec

• Cable Assemblies, Backplanes, Connectors

• Optical Fiber (Multi-Mode/Single-Mode), Optical Modules(Convert Electrical Signal to Light for long distance transmission)

– Intel/TI/Spectra7/AMD/ParadeTechnologies • Chips/IC, Packages, ULSI, VLSI

– Keysight/Anritsu/Rhode&Schwarz/Tektronix/TeledyneLecroy

• Test and Measurement Equipment – VNAs, TDRs/TDTs, Data/Pattern Generators, Eye Diagram, LCR Meter

15

How Are Systems Organized & Developed?

• Standards Bodies & Specification Documents – SFF

• Form Factor System Design. Look up SFF 8024 for widescope overview.

– IEEE • IEEE 802.3bj (100G Ethernet – 8 Diff Lanes @ 25Gbps) • IEEE 802.3ba (40G Ethernet – 8 Diff Lanes @ 10Gbps)

– Infiniband – SAS

• SAS 2.0 (6Gbps) • SAS 3.0 (12Gbps)

– FibreChannel – USB – HDMI – PCIE – For more check out:

• Handbook of Serial Communications Interfaces: A Comprehensive Compendium of Serial Digital Input/Output (I/O) Standards by Louis Frenzel [2015]

16

The Interconnects

• PCB Trace (Single-Ended Microstrip)

• PCB Trace (Differential Microstrip)

17

The Interconnects

• PCB Trace (Single-Ended Stripline)

• PCB Trace (Differential Stripline)

18

The Interconnects • Xsection of PCB

(“Stackup”) – Gives ultimate

description of the entire PCB build

• Vias – Connects Traces from

one layer to another. – Can easily destroy

the signal integrity of a channel. • Stub • XTALK • Reflections • Radiation of signal

into plane cavities. 19

Via

The Interconnects • Copper Cable Assembly

– HDMI, USB, QSFP, SFP, PCIE, DisplayPort, ……..

QSFP28 8 Differential

Channels (28Gb/s/lane)

SFP28 2 Differential

Channels (28Gb/s/lane)

HDMI High Speed 3 Differential Data Lanes (6Gb/s/lane),

1 Differential CLK

USB Type-C 3.1 Gen2 Speed

-Reversible -10Gbps Per High Speed Lane

-Can carry protocols like Display Port (“Alt. Mode”)

*Note: To actually BUILD & SELL certain

connectors and cables legally

requires a licensing contract. Some even

have very specific usages (USB).

20

The Interconnects • Copper Cable Assembly Anatomy:

Raw Cable

Backshell

Pull Tab

PCB w/ its Traces

Termination Region

Raw Cable X-Section

QSFP Example

Twin Axial Cable (“TwinAx”)

Typical Signal AWG 26AWG-32AWG

-Trade off between loss and flexibility

21

The Interconnects • Raw Cable: Differential Pairs only in this ppt.

– TwinAx, Shielded Twisted Pair, Unshielded Twisted Pair

Jacket

Jacket

TwinAx

Shielded Twisted Pair

(STP) “Cat 6e”

Braid

Foil Shield

Foil Shield

Filler

Drain

Dielectric Signal Leads

Signal Leads

Signal Leads

Signal Leads

Dielectric

Note: -STP typically has a drain and no braid but sometimes it does, as shown above. Raw Cable is about loss, feasibility of use (Bending, Twisting, etc.), & Environmental Reqs so there are tons of products from several manufacturers.

-The Drain/Braid sole function is to carry common signal to next devices and also EMI Control. -Typically conductors are solid core or stranded (Flexibility). Typically plated with Ag or Sn (Environmental)

22

The Interconnects • Twisted Pair (Real Photos)

When you buy raw cable, it typically comes in large bulk called “Spools”

which are made in batches. Companies keep up with batches &

label them with “Lot codes”.

Typical Dielectrics -FEP (Dk: 2.0 , Df: 0.0002) -PE (Dk: 2.1 , Df: 0.0020)

• Several Types • HDPE • LDPE • LLDPE

-Teflon®/PTFE (About same as FEP)

23

Connectors

• One of the worst enemies in channels with boards. • Connectors are notorious for being the number one most important

detail in determining the fastest speed of the entire channel. – It is the reflections caused by impedance discontinuity at the

connector that causes this. – The faster you go, the more complex the design becomes to control

impedance and xtalk.

24 QSFP Connector by Itself QSFP Connector on test board inside “cage”

Attitudes of the Interconnect

• Speed of Signal:

– v𝑝 ≈𝑐

𝜀𝑟

• Characteristic Impedance:

– 𝑍0 =𝑅+𝑗𝜔𝐿

𝐺+𝑗𝜔𝐶 ≈

𝑅+𝑗𝜔𝐿

𝑗𝜔𝐶 𝑠𝑖𝑛𝑐𝑒 𝐺 ≈ 0 𝑓𝑜𝑟 𝑚𝑜𝑠𝑡 𝑝𝑟𝑎𝑐𝑡𝑖𝑐𝑎𝑙 𝑠𝑖𝑡𝑢𝑎𝑡𝑖𝑜𝑛𝑠

• When R>>ωL (Low Freq), 𝑍0 ≈𝑅

𝑗𝜔𝐶 “RC Region”

– Very tiny interconnects e.g. chip level & package

• When R<<ωL (High Freq), 𝑍0 ≈𝐿

𝐶 “LC Region”

– “Normal” sized interconnects e.g. PCB Traces, Cable, Backplane

• The “boundary” between these two elements is inversely proportional to the size of the device. See next slide.

25

Characteristic Impedance

LC Region

RC Region

Microwave->

Audio Band

Twisted-Pair Cable (Nominal Z for Audio Application)

Notice the horizontal asymptote at 100Ohm. This is 𝐿

𝐶.

All uniform TEM Mode interconnects act in this manner. 26

Bottom Line:

– Most interconnects, except chips, in a TEM/Quasi-TEM microwave state operate at a single characteristic impedance.

• Examples – 85 Ohm Differential

– 100 Ohm Differential (Most Common)

– 50 Ohm Single Ended

27

Frequency Dependent Loss

• Loss doesn’t kill your design. Frequency Dependent Loss kills your design. This creates ISI and signal loss.

28

Signal Flow

• The speed of the signal is determined by the speed of the EM field compression wave traveling through the interconnect.

– It is not determined by speed of an electron.

• Signals do not propagate like the typical current they teach in grade school. They propagate in a certain fashion: (double click animations below)

29

Relating RLGC to SI of Interconnect

• Telegrapher’s model approximation is ONLY applicable (no exceptions) when the unit cell is much smaller (at least 1/6th) than the wave length of the frequency of interest. It is very common to convert from frequency to wave length in practice.

Len𝑔𝑡ℎ𝐼𝑛𝑡𝑒𝑟𝑐𝑜𝑛𝑛𝑒𝑐𝑡𝑀𝑎𝑥=𝜆𝑔

10=

𝑐

10 𝜀𝑟𝑓𝐼𝑛𝑡𝑒𝑟𝑒𝑠𝑡 𝑡𝑜 𝑚𝑒𝑒𝑡 𝑐𝑜𝑛𝑑𝑖𝑡𝑖𝑜𝑛

• If you would rather think in terms of just time then the highest

frequency of interest is:

𝑓𝐼𝑛𝑡𝑒𝑟𝑒𝑠𝑡 =1

10𝑇𝐷𝑒𝑙𝑎𝑦𝐼𝑛𝑡𝑒𝑟𝑐𝑜𝑛𝑛𝑒𝑐𝑡 𝑡𝑜 𝑚𝑒𝑒𝑡 𝑐𝑜𝑛𝑑𝑖𝑡𝑖𝑜𝑛

• Must ALSO be at least Quasi-TEM

30

RLCG in Action

• Simulation in HFSS (5mm TwinAx)

• 𝑓𝐼𝑛𝑡𝑒𝑟𝑒𝑠𝑡 = 7GHz ---> S-Parameter Output

• Convert to RLGC via W-Element Method

– Several softwares can do this

• Able to separate resistive and dielectric losses!

31

RLCG in Action

• Simulation in HFSS (5mm TwinAx)

• 𝑓𝐼𝑛𝑡𝑒𝑟𝑒𝑠𝑡 = 7GHz ---> S-Parameter Output

• Convert to RLGC via W-Element Method

– Several softwares can do this

• Able to separate resistive and dielectric losses.

32

RLCG in Action

33

Text from Advanced Signal Integrity for High-Speed Digital Designs [2009]

Big Picture

• Where do we start in understanding our devices better?

34

Waves as Phasors

• EM Waves actually wave like a hand wave.

– It is something moving back and forth

• How Fast?

• How Much?

• Where is it compared to other waves?

– Bottom Line:

• Natural Phenomena can be expressed as waves.

35

How is Data Sent?

• Typically, NRZ signals are sent down high speed SERDES channels. This is a time-domain signal. This is the real life signal. Think of the data as pulses.

• Unfortunately, it’s difficult to solve problems in just the time domain. This is where frequency domain becomes much easier to characterize devices.

36

DUT What

Comes Out?

Fourier Transform Square Wave (CLK Signal)

37

Thankfully, real signals can be transformed to the frequency domain!

• Bottom Line:

1) We know our signal : (NRZ, PAM4, RZ,…)

2) We can express the signal in frequency domain

3) We can use machines (VNAs) to inject thousands of waves into our devices and see how each wave acts (Magnitude and Phase Change)

4) Because of (1), (2), & (3) we can know how any real signal will change as it passes through our devices!

38

“Our Signal” “Our Device” “Our Output”

Major Caveat: LTI Systems ONLY.

NRZ PAM-4

S-Parameters

• Two Classes of Signals = Two classes of S-Parameters

39

𝑺𝒎𝒏 =𝑾𝒉𝒂𝒕 𝒚𝒐𝒖 𝒈𝒆𝒕 𝑶𝒖𝒕 𝑷𝒐𝒓𝒕 𝒎

𝑾𝒉𝒂𝒕 𝒚𝒐𝒖 𝒑𝒖𝒕 𝑰𝒏 𝑷𝒐𝒓𝒕 𝒏

Single Ended Examples S21 (Insertion Loss) S43 (Insertion Loss) S11 (Return Loss) S22 (Return Loss) S31 (Reverse Coupling) S23 (Forward Coupling)

Mixed-Mode

Mixed-Mode Examples SDD21 (Differential Insertion Loss) SCC21 (Common-Mode Insertion Loss) SCD21 (Mode Conversion) SDD11 (Differential Return Loss) SCC11 (Common-Mode Return Loss) SCD11 (Differential to Common-Mode Reflection)

Real Data Example

40

How Are S-Parameters Measured?

• Typically with Vector Network Analyzer (VNA) – Typical bandwidth:

• 10MHz up to 8GHz,20GHz,26.5GHz,50GHz,70GHz,110GHz

– Typical number of ports: • 2, 4, 16, 32 ports.

• For High-Speed SERDES applications, at least 4 ports are necessary.

• Most VNAs are 4-port, & if you need more ports, you can buy extension units.

41

4-Port VNA

12-Port Extension

Important Points of VNA Testing

• VNAs are intrinsically STUPID! – They MUST be CALIBRATED.

• Two types of calibration – Mechanical

» Many measurements needed to calibrate VNA

– Electronic » “ECAL”/”AutoCal” Units offer much

greater repeatability in calibration » Only a one or a few measurements

needed to calibrate VNA

• Several Methods – SOLT, TRL, QSOLT, Enhanced Response SOLT, etc…..

• SHOULD use phase/mag stable test cables • SHOULD use torque wrenches.

42

Keysight 20GHz 4-Port “ECal” Unit

Pulses

• Understanding the frequency spectrum of a pulse is key to understanding what does and does not matter in the frequency domain characteristics of your serdes channel

• To greatly simplify the problem, Think of a random NRZ sequence e.g. 00101001110110100101... as:

– 0 – “No Pulse” (Has no frequency data)

– 1 – “One Pulse” (Infinite frequency spectrum)

• Let’s understand what it takes to transmit a pulse.

43

Frequency Spectrum of A Pulse

• This is an ideal pulse.

44

=

Photo from High Speed Digital Design: Design of High Speed Interconnects & Signaling [2015]

UI(seconds)

GHz

𝑈𝐼 = 1

𝑓𝐵𝑎𝑢𝑑

• This is a real pulse.

45

=


GHz

Differential High Speed Channel

𝐓𝐫 = 𝐓𝐫𝐚𝐧𝐬𝐦𝐢𝐭𝐭𝐞𝐫 𝐑𝐢𝐬𝐞𝐓𝐢𝐦𝐞(𝟐𝟎%−𝟖𝟎%)

About 20-25% of UI 𝐅𝐑𝐗 = 𝐑𝐞𝐜𝐞𝐢𝐯𝐞𝐫 𝐁𝐚𝐧𝐝𝐰𝐢𝐝𝐭𝐡 Typically 𝐟𝐟𝐮𝐧𝐝𝐚𝐦𝐞𝐧𝐭𝐚𝐥 All of these are approximations though.

Edges are “slowed” & “smeared”

a.k.a. rise time degredation

• This is a real pulse.

46

=


GHz

` Differential High Speed Channel

𝐓𝐫 = 𝐓𝐫𝐚𝐧𝐬𝐦𝐢𝐭𝐭𝐞𝐫 𝐑𝐢𝐬𝐞𝐓𝐢𝐦𝐞(𝟐𝟎%−𝟖𝟎%)

About 20-25% of UI 𝐅𝐑𝐗 = 𝐑𝐞𝐜𝐞𝐢𝐯𝐞𝐫 𝐁𝐚𝐧𝐝𝐰𝐢𝐝𝐭𝐡 Typically 𝐟𝐟𝐮𝐧𝐝𝐚𝐦𝐞𝐧𝐭𝐚𝐥 All of these are approximations though.

Edges are “slowed” & “smeared”

a.k.a. rise time degredation

2 Different Channels – 5Gb/s

47


2 Different Channels – 20Gb/s

48


• Bottom Line: – Frequency Domain characterization and/or

measurements of devices gives a great first order approximation as to how well they will do at certain data rates.

– There are a lot of specifications that provide either “Normative” (Mandatory) S-Parameter Limits that your device must pass or “Informative” S-Parameter Limits that offer guidance for achieving good SI. • Informative S-Parameter Specs: 802.3bj Cable Testing

• Normative S-Parameter Specs: 802.3ba Cable Testing

49

802.3bj S-Parameter Limits Examples

50

25Gb/s

Informative

• Don’t forget…

– Signals are EM waves/voltages in time...

• The industry has learned that even if devices passed a specification’s S-Parameter limits, doesn’t mean that a given channel will work. Time-Domain is what is real. – 802.3bj saw this problem and created COM (Channel Operating

Margin) method. COM is a sophisticated time-domain based algorithm that determines a S/N of a channel in the presence of any number of XTALK aggressors. It uses the channel’s impulse response and compares it to a statistical noise cdf value at a particular BER.

– COM uses S-Parameters touchstone files as input.

51

TDR • Learn to physically relate to the device in time.

52

SMA Connector

Test Board Traces (PCB)

Connector

Raw Cable

Paddlecard

TDR Unshielded Twisted Pair

53

Remember Time? • It’s useful to see the channel response in time.

54

*

PRBS9 SDD21 Response

Coded Data

Eye Diagram

IFFT (SDD21(f)) “Golden PLL”

Good Quality S-Parameters from a Simulator or Measurement can be transformed to the time domain and provide data that easily shows the overall performance of the channel,

with or without equalization, as long at they represent an LTI system.

Eye Diagrams

• The final metric of judging a channel

55

Simulation from S-Parameters: Equalized HDMI 2 Eye

Measurement: Equalized HDMI 2 Eye

Eye Diagrams

• Can give information such as:

– Eye Height

– Eye Width

– Jitter (and it’s subcomponents)

– Amplitude Noise

– BER (Bit Error Rate)

56

Bit-Error Rate (“BER”)

• BER = # 𝐸𝑟𝑟𝑜𝑟𝑠

𝑈𝐼

• Can be either directly measured or extrapolated.

– It’s extremely difficult to measure low BER of devices. Why? It takes a loooooong time to do it.

– The next slide will show BER in a different way.

• It is normally a function of jitter, but can also be a function of amplitude noise.

57

BER in a Different Way

• Normal BER description is not intuitive. Instead ask the question:

– Within how many days will it take to get one error at a certain BER, for four different data speeds?

– Within how many years will it take to get one error at a certain BER, for four different data speeds?

58

Days

59

1

𝐵𝐸𝑅𝑓𝐵𝑎𝑢𝑑86400

This is the amount of time that it would probably take to get an error as a function of BER value for a particular device.

Notice how the data tells us how long it would take to characterize

a DUT's BER through Time-Domain BER Testing.

Years

60

1

𝐵𝐸𝑅𝑓𝐵𝑎𝑢𝑑86400 ∗ 360

This is the amount of time that it would probably take to get an error as a function of BER value for a particular device.

Notice how the data tells us how long it would take to characterize

a DUT's BER through Time-Domain BER Testing.

• Unfortunately, at 25G/s speeds today, there is a COM calculated S/N of ~5dB at a BER value of 10^(-5)!!!

• Sophisticated error corrections (Reed-Solomon for example) have to be put in place to not break the system! – Typically a polarity check

– No Forward Error Correction

– Forward Error Correction

– Power Consumption

61

• Measuring low BER values takes an extraordinarily long time, especially for lower data rates (5Gb/s)

• There are methods that can allow us to extrapolate using a practical sample size of data, whether that is s-parameters or eye diagram measurement.

62

Dual Dirac Model

• 1) Create a histogram of timing uncertainty as the zero cross points of eye diagram

• 2) We only care about the tails. We fit the histogram so that the distribution can be expressed by a Gaussian standard deviation and two dirac deltas.

• 3) Create CDF, use the width of the eye mask, then figure out BER Value of Channel.

63

Eye Mask

`

Timing Uncertainty Budget

BER Bathtub Plot

64

Eye mask width

example

BER Bathtub Plot

65

Eye mask width

example

10^(-10) BER Value in this

Example

Equalization • Most SERDES channels have to have EQ!

• Types of EQ – TX (FFE),(Pre/De-Emphasis)

– RX (CTLE – Active or Passive), (DFE), (FFE) 66

𝑻𝒓𝒚 𝒕𝒐 𝑨𝒄𝒉𝒊𝒆𝒗𝒆 𝑬𝑸(𝝎) =𝟏

𝑯 𝑪𝒉𝒂𝒏𝒏𝒆𝒍(𝝎)

Differential Pairs – Why?

• Typically, you will see differential pairs working at 1GHz and up in high speed serial channels.

• Tightly coupled Differential Signals on Differential Pairs are, more often than not, extremely robust to return path discontinuities and external noise. This is because in the absence of a return path, proximity effect of the two conductors with equal and opposite current flows distort the surrounding magnetic field potential causing a strong concentration of current flow (and therefore EM field potential) between the conductors.

• 2x the signal pins but less power and gnd pins in packages and connectors.

• CMMR = 𝑆𝐷𝐷21

𝑆𝐶𝐶21 ex) Helical/Spiral Wrap TwinAx Cable

67

Mixed Mode S-Parameters

• Frequency Domain: – Reflection

• SDD11/22 (Differential Return Loss)

• SCC11/22 (Commmon-Mode Return Loss)

• SCD/SDC/11/22 (Imbalance Reflections)

– Transmission • SDD21 (Differential Insertion Loss)

• SCC21 (Common-Mode Insertion Loss)

• SCD21 (Mode Conversion)

• SCD21-SDD21 (Loss independent Mode Conversion)

68

Mixed Mode S-Parameters • Use scripts (python), AtaiTec ADK, Keysight PLTS, Teledyne Lecroy SI Studio, or

other freeware to look at all these s-parameters in time domain. • Also look at all of the single ended parameters, in frequency domain

and also time domain. • Rules for S-Parameter Setup:

– 𝐹𝑟𝑒𝑞𝑆𝑡𝑜𝑝−𝐹𝑟𝑒𝑞𝑆𝑡𝑎𝑟𝑡

∆𝐹𝑟𝑒𝑞+ 1 = # 𝑜𝑓 𝑃𝑜𝑖𝑛𝑡𝑠

– 𝑇𝑅𝑖𝑠𝑒𝑇𝑖𝑚𝑒20−80 ≈

.23

𝐹𝑆𝑡𝑜𝑝

– 𝑇𝑅𝑖𝑠𝑒𝑇𝑖𝑚𝑒10−90 ≈.35

𝐹𝑆𝑡𝑜𝑝

– 𝑇𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝐼𝑚𝑝𝑢𝑙𝑠𝑒 =1

∆𝐹𝑟𝑒𝑞

– ∆𝑡𝐼𝑚𝑝𝑢𝑙𝑠𝑒 =1

2𝐹𝑆𝑡𝑜𝑝 + ∆𝐹𝑟𝑒𝑞

– Max 𝐿𝑒𝑛𝑔𝑡ℎ𝐷𝑈𝑇 =𝑆𝑖𝑔𝑛𝑎𝑙 𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦

4∆𝐹𝑟𝑒𝑞 ≅

11.8

4∆𝐹𝑟𝑒𝑞𝐺𝐻𝑧 𝜀𝑒𝑓𝑓𝑖𝑛𝑐ℎ𝑒𝑠 =

.3

4∆𝐹𝑟𝑒𝑞𝐺𝐻𝑧 𝜀𝑒𝑓𝑓 (𝑚)

• Theoretically 2 is all that is needed to account for thru and reflection measurements of a DUT. HOWEVER, it normally takes multiple round trips for the energy of the response to die out. These round trip spurts are called “re-reflections”. So 4 is a good rule of thumb. In low-loss cases, a number greater than 4 may be needed. How to tell? Look at the time domain response.

69

Problems to Master in SI • There are way too many SI issues to cover in power point.

– Best thing to do is to read a fundamental text. – Bethesignal.com has some of the best introductory courses. I highly

recommend it. Very cheap and extremely effective. – PCB Design: Fedevel Online PCB Academy – University of Oxford – DesignCon

• Some Recommended Texts: – Advanced Signal Integrity for High-Speed Digital Designs [2009] – Understanding Signal Integrity [2011] – Signal Integrity Characterization Techniques [2009] – High Speed Digital Design - A Handbook of Black Magic [1993] – High Speed Digital Design - Design of High Speed Interconnects and Signaling

[2015] – Signal and Power Integrity - Simplified (2nd Edition) [2009] – Complete PCB Design Using OrCAD Capture and PCB Editor [2009] – The Foundations of Signal Integrity [2010] – Fundamentals of Vector Network Analysis [2014] – Handbook of Microwave Component Measurements: with Advanced VNA

Techniques [2012] 70

A Few Rules of Thumb • Learn to understand both Resistive & Dielectric and then make smart material decisions. • Make distances between discontinuities as SHORT AS POSSIBLE • When designing a PCB, ALWAYS contact a PCB Board House and talk to them about their capabilities

and tolerances on key items. • Not everything has to be nominal impedance. • Try to never do something without knowing what’s going to happen next.

• EXPERIMENT! • Become an expert with s-parameters, instrument calibration, & de-embedding • Learn simulation software:

– 3D: HFSS, Simbeor THz, Keysight ADS, Siwave, Microwave Studio, etc… – 2D: Q3D, ADK x2D, QuickField

• 2D Field Solvers help tremendously during optimization phase and also for quickly making arbitrary uniform transmission line s4p models.

• Measure everything. Period. • IL of channels should start at 0dB and RL & Coupling S-Parameters should be at a large negative dB

value if in LC Region. • Become very familiar with dB. However, don’t forget about linear scale. • XTALK will skyrocket if wide reference planes are removed. • Understand proximity effect and how it can affect losses/impedance/XTALK • Understand Clock Architectures. • Subscribe to SI-List (FreeList.org) • If you can’t manufacture it, it is worthless. • Single Ended S-Parameters are close to meaningless for extremely tightly coupled diff pairs. • Argue. Don’t let marketing or management be your puppet master. • Study. Period.

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