Design_World_-_Internet_of_Things_Handbook_April_2020

20 DESIGN WORLD — EE NETWORK 4 • 2020 eeworldonline.com | designworldonline.com

Designers must look at and characterize the entire

Type-C ecosystem when testing USB4 designs.

How to test USB4 designs

The USB Type-C connector has received signifi cant

adoption with ubiquitous standards like USB, DP, and

Thunderbolt. The next-generation variant of USB is USB4.

USB4 will transmit and receive on all four lanes of the Type-C

connector in parallel, with bonded rates of 40 Gbps in each

direction for an 80-Gbps link.

As these signals get sent through even longer passive

cables, specialized transmitter and receiver techniques are

necessary to preserve signal integrity. They involve new

equalization requirements, signaling technologies, and

measurement methodologies. Here, equalization at the

transmitter and/or receiver serves to mitigate the effect of

intersymbol interference and hence, to minimize the bit

error rate (BER). In equalization, the signal passes through

a fi lter having its frequency response equal to the inverse

of the channel frequency response. A high gain is applied

at higher frequency to counter the signal attenuation at

the high frequencies. In simple words, equalization is an

adaptive fi lter with coeffi cients determined at runtime

depending upon the physical channel. It takes ultra-low-

noise test instruments to properly characterize these high-

speed signals.

The USB4 standard was announced in Q1 of 2019

and the specifi cation published in August 2019. Typically,

there is often a more lengthy

time-lag between the standards

announcement and the

specifi cation release. But there

INTERNET OF THINGS HANDBOOK

Jit Lim • Keysight Technologies

Test point Description Comments

TP1 Transmitter IC output Not used for electrical

testing.

TP2 Transmitter port

connector output

Measured at the plug side

of the connector.

TP3

Receiver port connector

output

Measured at the

receptacle side of

the connector. All the

measurements at this

point shall be done

while applying reference

equalization function.

TP3 Receiver port connector

input

Measured at the plug size

of the connector.

TP4 Receiver IC input Not used for electrical

testing.

Test points for USB4 compliance testing

Source: USB Implementers Forum

Package Package

IC IC

TXp

TXn

TP1 TP2 TP3’ TP3 TP4

The test points and

their and defi nitions

as spelled out for

USB4 compliance

testing.