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How to test USB4 designs Designers must look at and characterize the entire Type-C ecosystem when testing USB4 designs.
Jit Lim • Keysight Technologies
The USB Type-C connector has received significant 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
Test points for USB4 compliance testing 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.
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 filter 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 filter with coefficients determined at runtime depending upon the physical channel. It takes ultra-lownoise test instruments to properly characterize these highspeed signals. The USB4 standard was announced in Q1 of 2019 and the specification published in August 2019. Typically, there is often a more lengthy time-lag between the standards TP1 announcement and the specification release. But there
The test points and their and definitions as spelled out for USB4 compliance testing.
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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.
Source: USB Implementers Forum
TP2
TP3’
TP3
TP4
+ -
TXp TXn
IC Package
4 • 2020
IC Package
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