Breakthrough Developments in TDR/TDT Measurement Technology

Kevin Kershner

Digital Systems

Specialist

May 13, 2014

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Agenda

•Introduction 5 min

•TDR/TDT and S-parameters 15 min

•Hot TDR Measurements 15 min

•Q&A 5 min

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As data rates increase:

• Design margins decrease:

• inter-symbol interference (ISI)

increases due to

channel/interconnect losses and

reflections

Characterize signal integrity issues using Scope and Vector

Network Analyzer (VNA) based TDR/TDT Solutions

Introduction

• Trend toward parallel/multi-lane

architectures

• increases crosstalk concerns

Demanding Applications for TDR/TDT Measurements

SI Lab

(PCBs,

interconnects,

connectors…)

Production Test

of cables,

connectors,

interconnects

S-Parameter

generation for

de-embedding

Active Device

Characterization

Research

•Fast edge and high

BW to isolate

impedance issues

•Easy to use.

•Many channels

•Low capital cost

•High accuracy

•Fast calibration

•Fast to program

•Compliance

Applications

•Easy to generate S-

parameter files •Hot TDR

measurements

•High accuracy (fast

step, high BW)

•Flexibility

Targ

et

applic

ations

Measure

ment

needs

4

ENA Option TDR is an optimal solution up to 20 GHz

Simple and intuitive operation

Fast and accurate measurements

High ESD robustness

PNA is the “Gold Standard” for S-Parameter

measurements

Superior dynamic range vs. TDR

Preferred by many RF/Microwave engineers

Scope-based TDR/TDT

Preferred by many digital designers

Useful for quick troubleshooting, fault location analysis

Measures down to DC (vs. 9 kHz)

Waveform, eye/mask, jitter measurements

Less expensive than VNA with similar bandwidth

Page 5

VNAs vs. TDR Oscilloscopes

Complement

each other

Most SI labs have both

solutions.

Agenda

•Introduction 5 min

•TDR/TDT and S-parameters 15 min

•Hot TDR Measurements 15 min

•Q&A 5 min

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Quick Review – TDR Time Domain Reflectometry (TDR)

• Impedance measurements

• Locate the position and nature of each

discontinuity

• Propagation/Time delay

• Excess Reactance

(Capacitance or Inductance)

• Effective dielectric constant

TDR (Impedance Profile)

S-parameters (Return Loss) FFT

1

2

3 4

5 6

1. Reference Plane 2. Connector Launch 3. Uncoupled TX Line 4. Coupled Diff TX Line 5. Connector 6. Open Circuit

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Quick Review – TDT

Time Domain Transmission

(TDT)

• Step Response

• Propagation/Time delay

• Propagation velocity

• Rise time degradation

• Near-end crosstalk (NEXT)

• Far-end crosstalk (FEXT)

• Skew

TDT (Step Response) S-parameters (Insertion Loss)

FFT

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S-Parameters and TDR/TDT

Return Loss or TDR

Insertion Loss or TDT

Near End Crosstalk (NEXT)

Far End Crosstalk (FEXT)

Four-port single-ended device

Port 1

Port 3

Port 2

Port 4

Frequency Domain Parameters Time Domain Parameters FFT

IFFT

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Together, TDR/TDT and S-Parameters provide

tremendous insight

TDR

Z profile

TDT

Step Response

S11

Return Loss S21

Insertion Loss

TDR and S21 are most intuitive, insightful.

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Edge speed determines two important parameters:

1. TDR Resolution: The faster the edge, the closer two impedance

discontinuities can be identified as separate events on the TDR trace.

What TDR edge speed should I use?

2. Max S-parameter frequency

A step with a fast edge has higher

frequency content and enables S-

parameter testing to a higher frequency.

•

• Ɛ = dielectric constant of the transmission

system

• c = speed of light in a vacuum.

Dmin=

For Ɛ = 4 and system rise time of 8

ps, Dmin < 1mm.

D D

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What TDR edge speed should I use? Select a solution based on your application:

• Too fast: you’ll see impedance discontinuities that will not affect the real

signals in your design (you’ll waste time fixing things that do not matter)

• Too slow: discontinuities are masked

Choose your TDR edge speed:

1. Full Characterization “Rule of Thumb”: use TDR edge speeds that are

minimum 2x faster than the rise times of your design

2. Compliance Test: use 20%-80% TDR edge speed specified by Standard

25ps

100ps

500ps

200ps

TDR Two-Event Resolution (Spatial-Resolution )

To increase the two-event resolution of the TDR

system, three items are considered: 1. Increase the speed of the step generator

2. Increase the bandwidth of the oscilloscope

3. Minimize the bandwidth-limiting effects of the test system

- minimize use of adapters, cabling

- use good quality fixturing

- compensate for losses using TDR

calibration (de-embedding)

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• Electronic Calibration (ECal)

DC-67 GHz module support

N1055A Bandwidth

• 35 GHz (2.92mm)*

• 50 GHz (1.85mm)

• Fastest TDR Edge Speed

Up to 8 ps (typ) 50 GHz, yields highest

TDR resolution.

N1055A Connector Type

• Male

• Female

• Highest Channel Count - Up to

16 channels per mainframe.

• Single-ended and

Differential Device Testing

(True-Mode Stimulus)

• High-Bandwidth Oscilloscope

N1055A operates in receiver-only mode.

• Built-in Electrostatic

Discharge (ESD) Protection

• Calibrated impedance

and S-parameter results

displayed in real-time

• Adjustable TDR Edge

Speed

• Calibration Made Easy

using ECal modules or

mechanical SOLT standards.

86100D DCA-X with N1055A 35/50 GHz TDR/TDT Modules A fully integrated TDR/TDT/S-parameter measurement system that provides calibrated

impedance and S-parameter analysis on up to 16 channels in real-time.

N1055A Channel Count

• 2 Channels per module*

• 4 channels per module

• Ultra-thin remote heads

- minimize adapters/cables

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* upgradeable

N1055 A Options:

Agenda

•Introduction 5 min

•TDR/TDT and S-parameters 15 min

•Hot TDR Measurements 15 min

•Q&A 5 min

15

Why Measure Hot TDR?

TDR(Time Domain)

OFF

1333Mbps (active)

334Mbps (active)

ohm

dB

1G 2G 3G 4G 5G 6G

freq(Hz) 666M

•Hot TDR measurement is the impedance analysis of active devices under

actual operation conditions.

•Typically, impedance of the device in the OFF state and ON state (Hot

TDR) is significantly different. Impedance may vary with the data rate as

well.

Return Loss (Freq Domain)

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2. Partial reflection

from Rx due to

impedance

mismatches …

Eye

Degradation

Channel Tx Rx

1. Signal transmitted from Tx …

3. Re-reflection

from Tx due to

impedance

mismatches ...

Multiple Reflections

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Source Impedance Matched Source Impedance NOT Matched

Source Termination Effects

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Many Standards Require Hot TDR Measurements

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MFTP from Tx

7.4.13 Return Loss and Impedance Balance

Transmitters (Tx):

When measuring output impedance of transmitters the operating condition

shall be during transmission of MFTP. This is to assure the measurement

is performed during a mode of operation that represents normal operation.

How to avoid effects of the

transmitter signal on

measurements?

Measurement Challenge

Serial ATA

20

t

freq fc

•wideband receiver captures all of the

signal energy from the transmitter

time

Extensive averaging is

necessary to obtain a stable

waveform.

fc

freq

•narrowband receiver minimizes the effects

of the data signal from the transmitter

time

In many cases, averaging is

not necessary to obtain a

stable waveform.

t t

t

t

t

Tx Tx

Minimizing Errors from the Transmitter Signal TDR Scopes VNA

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Spurs due to Tx signal Fluctuations due to Tx signal

Avoid Spurious Feature

TDR(Time Domain) Return Loss (Freq Domain)

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From the data rate (user input), spurious

frequencies are determined and

automatically avoided during the sweep.

TDR(Time Domain) Return Loss (Freq Domain)

1-click

Operation

Avoid Spurious Feature

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Frequency Domain Time Domain 3 Breakthroughs

for Signal Integrity Design and Verification

Eye Diagram

ESD protection inside

Simple and Intuitive Operation

High ESD Robustness

Fast and Accurate Measurements

The ENA Option TDR is application software embedded on the ENA,

which provides a one-box solution for high speed serial

interconnect analysis.

What is ENA Option TDR?

www.agilent.com/find/ena-tdr

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•Multiple reflections due to

impedance mismatches

significantly impact signal integrity.

•Typically, impedance of the device

in the OFF state and ON state (Hot

TDR) is significantly different.

Impedance may vary with the data

rate as well. Therefore it is essential

to characterize the device under

actual operating conditions.

www.agilent.com/find/ena-tdr

Summary

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