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Keysight Technologies
USB 2.0 Compliance Testing
with Infiniium Oscilloscopes
Application Note
Introduction
Universal Serial Bus (USB) burst on the scene in 1995 delivering Who Should Read This
a revolutionary way to connect personal computers and devices. Application Note?
Allowing hot-plug capability, USB has introduced ease-of-use to Digital designers and developers
the PC device market by providing a simple connection scheme working towards USB 2.0 compliance.
and protocol for a wide variety of computer devices, ranging from
keyboards and mice to high-bandwidth devices such as printers,
scanners, and cameras.
Table of Contents
USB has now successfully replaced aging serial and parallel
ports as the connection of choice for both device manufacturers Introduction . . . . . . . . . . . . . . . . . . . . . .2
and end users. Whereas cable length and device expansion Basic Specifications . . . . . . . . . . . . . . .3
were limitations with older serial and parallel connections, they Full/Low-Speed Test Suite . . . . . . . . . .4
are no issue for USB. Amazingly, it allows devices to exist up to
Full/Low-Speed Test Fixture. . . . . . . . .4
30-meters away from the host, and allows up to 127 devices to
Signal Quality Test. . . . . . . . . . . . . . . . .5
be connected to a single host and port at once through a series
of USB hubs. The ability to talk directly to devices or to devices In-Rush Current Check . . . . . . . . . . . . .7
through hubs allows for this incredible expansion capability. Droop and Drop Testing . . . . . . . . . . . .8
Back-Drive Voltage Test . . . . . . . . . . . .9
USB 1.1 worked best for slower human-interface devices such as Hi-Speed Electrical Test Suite . . . . . . .9
mice and keyboards, with low-speed operating at 1.5-Mb/s and Hi-Speed Electrical Test Tool . . . . . . . .9
full-speed operating at 12-Mb/s. Higher-bandwidth devices were
Hi-Speed Test Fixture . . . . . . . . . . . . .10
severely limited by these relatively slow data transfer rates. As a
Hi-Speed Signal Quality Test . . . . . . .11
result, the USB-Implementers Forum (USB-IF) introduced the fully
backward compatible USB 2.0 in May 2000, which resulted in a Monotonicity . . . . . . . . . . . . . . . . . . . .11
40-fold increase in data throughput for hi-speed over full-speed. Packet Parameters Test . . . . . . . . . . .12
USB 2.0 operates at 480-Mb/s--ideal for devices such as video- Receiver Sensitivity. . . . . . . . . . . . . . .12
conferencing cameras and high-resolution printers. For more CHIRP Timing Test. . . . . . . . . . . . . . . .13
information, see the official USB-IF (USB Interoperability Forum) Impedance Measurements. . . . . . . . .14
website at www.usb.org.
Basic Specifications
As listed previously, USB 2.0 comprises three different data transfer rates--low-
speed, full-speed, and hi-speed.
Four wires compose the cable system--VBUS, D+, D-, and ground. Devices may be
either bus-powered, with 500-mA maximum bus current withdraw, or self-powered,
meaning they have their own power supply. D- and D+ is a differential signal
pair that serves as the primary information carrier between the host, hubs, and
devices. USB 2.0 supports three different types of data transfer: interrupt, bulk, or
isochronous. Control packets containing commands or query parameters may also
be sent by the host.
The flexibility inherent in USB is a direct result of the specifications above and the
stringent regulations and compliance testing mandated by the USB-IF. There are
three kinds of compliance tests: framework test, interoperability test, and electrical
test. This document only discusses Infiniium's electrical test solution.
Low, full, and hi-speed USB require compliance with the signal quality, in-rush
current check, droop/drop and back drive voltage electrical tests. Hi-speed
requires compliance with an additional suite of electrical tests--hi-speed signal
quality, receiver sensitivity, CHIRP timing, and packet parameters. Older methods
of compliance testing included first capturing the signals on a scope, then moving
the data to a PC so it could be cropped, stored in a .tsv format, and finally analyzed
in MATLAB. The Keysight Technologies, Inc. Infiniium USB Test Option is the first
scope solution in the industry that utilizes the official USB-IF MATLAB script. As
the result, it provides an affordable, trustworthy, single-box, compliance solution--
allowing you to say, as did one of our customers, "I know I'm going to pass!"
Data Rates Rise Times
Low-speed (LS) 1.5 Mb/s 75 ns