Test Solutions for USB - Backgrounder

The Universal Serial Bus (USB) was first introduced in 1995 and delivered a new way to connect personal computers and devices, essentially replacing aging serial and parallel ports as the connection of choice for device manufacturers and end users.

Since the introduction of USB, the USB-Implementers Forum (USB-IF) has continued to launch new variants of the interface standard. In 2000, the USB-IF announced USB 2.0 to provide increased data throughput for higher-bandwidth devices. USB 2.0 operates at up to 480 Mbps making it suitable for devices such as video-conferencing cameras and high-resolution printers.

One of the biggest factors in the incredible success of USB has been the successful interoperability of USB devices and hosts. Interoperable products are an indirect results of the compliance testing program developed and maintained by the USB-Implementers Forum (USB-IF).

Now a further enhancement to the USB platform has been announced with the release of USB 3.0 (SuperSpeed USB). USB 3.0 is backward compatible with earlier versions and has been designed to address the high bandwidth transport requirements of rich media, video and large digital files. USB 3.0 provides a 10-fold increase in the data transfer rates compared with USB 2.0 with a data rate specified as up to 5Gbps and data throughput greater than 200MB/s.

The family of USB specifications, USB 2.0, wireless USB and now USB 3.0, meet the needs of different applications and it is anticipated that all will co-exist in the market. Designers will choose the specification to meet the particular needs of their product. Whatever choice is made a robust test methodology is required to ensure that the end product is compliant to the relevant standards.

The continuing evolution of USB has been characterized by ever increasing data rates. USB 2.0 provided the choice of three data rates, Low speed at 1.5 Mb/s for compatibility with USB 1.1, Full speed at 12 Mb/s and High speed at 480 Mb/s. USB 3.0 further extends the data rate to 5 Gb/s. The architecture of USB is such that all of these data rates can co-exist at the same time within a configuration, all controlled by a common PC host.

This gives the flexibility to mix and match peripherals with different needs in terms of speed and throughput. This flexibility is one of the major advantages of USB and it arises directly from the stringent regulations and compliance testing mandated by the USB-IF.

For designers of USB devices and systems the successful completion of the compliance test regime is essential to ensure conformance to the standards and interoperability requirements. Each variant of USB has its own Compliance Test Specification. A number of the tests are common between variants, however, as the data rates increase then the requirement for a more thorough testing of high-speed effects increase. RF effects need to be considered when validating the high-speed modes of USB 2.0 and for USB 3.0.

Agilent Technologies offers a portfolio of solutions for testing USB, addressing all of the current variants. The company participates actively in the USB Implementers Forum (USB-IF) allowing it to influence and respond rapidly to changes in the test specifications. Agilent's USB-IF approved test solutions are used in compliance workshops and by test labs worldwide.

The USB 2.0 cabling system comprises four wires, two signal (D+ and D-), power (Vbus) and ground. D+ and D- are configured as a differential signal pair used in NRZI half-duplex mode and serve as the primary information carrier between the host, hubs and peripherals. Devices may be either bus powered with a limit of 500mA current drain or self powered using an in-built power supply.

USB 2.0 specifies three different data rates, low speed at 1.5 Mbps, full speed at 12 Mbps and high speed at 480 Mbps. All three data rates can exist concurrently in a network of USB devices. Any peripheral device on the bus must be able to communicate with its hub; hubs must be able to communicate with the host, each other, and up to seven peripherals.

To ensure compliance with the USB 2.0 specification products require extensive testing. To prove compliance and achieve certification by the USB-IF requires that signal integrity, current and voltage parametric, and data integrity testing passes test specification requirements with approved USB-IF test tools. In addition to high speed signal quality, High-speed USB 2.0 certification includes testing of receiver sensitivity, CHIRP handshake timing, packet parameters and other tests.

Signal Quality Tests

The basic USB 2.0 electrical test suite includes signal quality, in-rush current and voltage droop/drop tests. For signal quality testing an oscilloscope is used to observe the signals being transmitted and received. The oscilloscope allows a range of parameters to be measured including signal eye, end of packet width, signaling rate, rise/fall times, crossover voltage and jitter.

Agilent Infiniium 9000 Series oscilloscopes together with Agilent probes and test fixtures can be used to reproduce the USB-IF specified tests. The Agilent USB Compliance Test Software makes USB signal integrity compliance testing as simple as making an automatic measurement. By integrating a run-time version of MATLAB within the oscilloscope for use with the USB-IF test scripts the USB Compliance Test Software provides a one-box solution to speed signal quality testing.

Data Integrity Test

Determining the cause of a data error or a performance problem in a USB network can be challenging. Logic and protocol analysis allows to see data traffic, make critical timing measurements, and verify protocols, making it the ideal tool for detecting and debugging higher-level data integrity problems.

The Agilent Infiniium 9000 Series Mixed Signal Oscilloscopes include integrated built-in logic and protocol analysis capabilities. The in-scope protocol viewer and debug application software with protocol triggering and USB serial decode allows debug and testing capabilities to be extended without the use of additional test equipment.

High Speed Tests

High speed USB 2.0 requires that high speed signal quality, receiver sensitivity, CHIRP timing and packet parameters are tested. Since the connection scheme for USB 2.0 uses a single pair of wires for both transmit and receive paths high speed signal quality testing has to be sequenced between sending a stimulus and then measuring the response.

Agilent’s USB 2.0 Receiver Test Library utilises the Agilent 81134A pattern generator and an Infiniium oscilloscope for extensive receiver testing. The device under testis put into the SEO NAK mode and the pattern generator is used to apply an amplitude and bit pattern controlled stimulus to test the sensitivity level of the receiver. The Infiniium oscilloscope test software automatically controls the signal source to easily and quickly sequence through the required tests. The receiver sensitivity and squelch thresholds are then measured using the oscilloscope.

Together with the USB Compliance Test Software (N5411A, N5990A) this ensures that products are tested to be fully compliant to the USB 2.0 specification requirements.

USB 3.0 has been introduced to keep pace with today’s performance demands of USB 2.0. Although high speed USB 2.0 is specified with a data rate of 480 Mbps the real data throughout is typically much less with I/O performance limitations allowing at best 35MB/s.

When downloading larger files higher throughput is required to allow manageable transfer times. USB 3.0 provides up to 5 Gbps data rate and greater than 200 MB/s data throughput.

To achieve this higher level of performance USB 3.0 adds 4 additional wires to the interconnection. The cabling system comprises 8 wires in total, 4 of these conform to USB 2.0 and are used to ensure backward compatibility. The additional wires are configured as two additional pairs that are dedicated to USB 3.0 communications. These operate in Full Simplex mode with one pair for transmit and one for receive.

The 10-fold increase in data rate of USB 3.0 poses new challenges in testing the transmitter, receiver and cabling system.

Transmitter Tests

For USB 3.0 transmitter testing compliance must be measured at the end of a 'compliance channel' with SMA termination for the transmitter signals using a phase matched SMA cable. Agilent's USB 3.0 test fixture provides a high performance USB 3.0 signal breakout with support for both transmitter and receiver testing with the correct SMA terminations.

When testing the transmit path a high-speed oscilloscope must be used to measure the transmitted waveform using a compliance pattern. This will allow eye diagram analysis and the measurement signal amplitudes, jitter, average data rate and rise/fall times.

Agilent's 90000 Series of oscilloscopes provide up to 13 GHz of bandwidth. Together with the U7243A USB 3.0 Transmitter Compliance Test Application the oscilloscope can used to perform transmitter compliance and validation testing as defined by the USB 3.0 specification.

Receiver Tests

USB 3.0 specifies an error counter within the device that can internally check the error performance of the receiver. The specification also provides test modes that include the ability to loop back the received data over the device's transmitter.

Testing receiver sensitivity requires a controlled stimulus or pattern generator which can provide a calibrated jitter input to the receiver under test. Measuring using the integrated error counter requires the use of an oscilloscope or BERT to read and decode the resulting value. Without an internal error counter testing in asynconous loopback mode requires a BERT or protocol analyzer to evaluate the resulting bit stream for errors.

The error counter approach is limited to the compliance pattern that can be recognised by the internal device. Although this is adequate for simple pass/fail testing it does not allow for debugging and characterization. Generally receiver stress testing is used to characterize the performance of the USB device under varying conditions of amplitude and jitter. It requires a pattern generator that can apply these different conditions including the ability to generate true random jitter for the target BER.

Agilent's portfolio of test solutions addresses all of these issues. For USB 3.0 the Agilent Technologies J-BERT can generate the patterns necessary to stimulate the device, including the ability to stress the device for jitter tolerance testing. Agilent's BERT together with SuperSpeed protocol analysis solutions can be used in loopback mode to characterize the resulting performance of the device.

Fast, reliable test automation is achieved with the N5990A Test Automation Software Platform. N5990A provides convenient control about the test instruments from a standard PC. It enables efficient compliance testing and characterization, including automated calibration.

Channel Tests

Due to the increased bandwidth of USB 3.0 more testing is required for cables, connectors and channel validation. TDR/TDT measurements are essential to ensure that designs meet the differential impedance and skew targets. VNA measurements are necessary to allow verification of return loss, insertion loss and near/far end crosstalk requirements.

“We are working closely with developers of SuperSpeed USB technology to ensure our solutions completely meet the needs of engineers testing for USB 3.0 compliance,” said Jim Choate, USB program manager at Agilent

Agilent's USB compliance portfolio meets the compliance test coverage requirements defined by the USB-IF, USB 3.0 specification announced by the USB-IF on Nov. 17, 2008. USB 3.0, known as "SuperSpeed USB" will deliver 10 times the data transfer rate of USB 2.0 and make power usage more efficient. SuperSpeed USB will be necessary for data-storage devices transferring more than 25 Gbps. Industry experts expect manufacturers to adopt SuperSpeed USB by the end of 2009 and to have consumer products widely available in 2010. However, until the actual silicon is available for testing, no USB solution will be ready for official certification.

Agilent's USB Test Solutions

Agilent provides test solutions for USB 2.0, USB 3.0.

N5416A USB Compliance Test Software

The N5416A compliance test software for Infiniium oscilloscopes gives a fast and reliable way to verify USB electrical specification compliance for USB 2.0 hosts, hubs and devices. The software executes the official USB-IF MATLAB scripts with MATLAB's runtime engine embedded in the oscilloscope for guaranteed correlation with official USB-IF test requirements. The software also automates the receiver testing providing the fastest receiver testing and compliance verification tools available.

Infiniium 9000 Series Oscilloscopes

The Infiniium 9000 Series mixed signal oscilloscopes provide analog bandwidths of up to 4GHz and built-in logic and protocol analysis. In addition to impressive analog specifications the Infiniium 9000 includes fast, integrated 2GSa/s digital channels and an in-scope protocol viewer for USB.

Low, Full and High Speed Test Fixtures

Agilent offers a range of test fixtures that meet the requirements of the USB-IF compliance test specification. For low and full speed compliance testing an E2646A SQuIDD (Signal Quality inrush Droop Drop) test fixture is required. High speed USB compliance testing requires the E2649A/B fixtures. For On-The-Go (OTG) USB testing Agilent offers the industries only OTG Electrical Test (OET) fixture.

USB 2.0 Receiver Test Software

The Agilent USB 2.0 receiver test software N5990A option 102 complements the N5416A compliance test suite with additional receiver tests including intra-pair skew, jitter tolerance, carrier skew, squelch test and differential sensitivity tests. For receiver testing the N5990A option 102 is used in conjunction with an Agilent 81134A pulse pattern generator and an Infiniium oscilloscope. N5990A option 202 provides full integration of the N5416A tests and thus enables e.g. consolidated Microsoft ® Excel™ test report.

Agilent's well established position as the leader in RF, Microwave and Digital design and test allows it to apply its expertise to the Super-speed testing needs of the USB3.0 standard. Agilent's test portfolio provides solutions for all aspects of USB 3.0, the transmitter, the receiver and the cabling system.

USB 3.0 Transmitter Compliance Test Application U7243A

Electrical Performance Validation and Compliance Software for the Infiniium Oscilloscopes
The U7243A USB 3.0 compliance test software for Infiniium oscilloscopes offer a fast and accurate way to validate and debug USB 3.0 silicon, host, hub or device. The U7243A software provides industry leading automated test support for USB 3.0 products and displays the test results in a comprehensive test report. In additional to the measurement data, the test report provides margin analysis that provides details on how close the device performance is to the specification requirements. For best measurement accuracy use the Agilent U7242A USB 3.0 transmitter and receiver test fixtures. Agilent's USB 3.0 test solution is designed from the ground up with the needs of the test engineer in mind.

DSO/DSA91304A Real-time 13-GHz Oscilloscope

The DSA90000A Series is built around an Infiniium DSO90000A Series oscilloscope and includes standard 20 Mpts of memory, clock recovery and real-time eye diagrams (SDA), basic jitter and RJ/DJ separation (EZJIT+), and bandwidth/noise reduction software included in a bundle that provides the right set of tools to debug even the most complicated signals.

USB 3.0 Test Fixtures - Agilent U7242A USB 3.0 Electrical Test Fixture

The U7242A USB 3.0 Test Fixture will help simplify the USB 3.0 measurement process by providing access to the transmitter and receiver measurement points required for USB 3.0 compliance testing.

• Provides test point access for transmitter measurements
• Single ended measurements as required by the USB 3.0 specification for transmitter and receiver validation and compliance testing
• Differential measurements using active probes allow probing of active bus transactions for debug and verification testing
• USB 3.0 power probing features for easy measurement of transient and steady state power states

J-BERT N4903B High-Performance Serial BERT

The J-BERT N4903B high-performance serial BERT provides the most complete jitter tolerance test for embedded and forward clocked devices. It is the ideal choice for R&D and validation teams characterizing and stressing chips and transceiver modules that have serial I/O ports up to 7 Gb/s or 12.5 Gb/s. It can characterize a receiver’s jitter tolerance and is designed to prove compliance to today’s most popular serial bus standards such as USB 3.0. For generating de-emphasized signals for USB 3.0 the J-BERT can be used with the de-emphasis signal converter N4916A/B. For generating LFPS signals the serial bus switch N4915A-005 can be used to switch J-BERT outputs to lower voltage levels. J-BERT handles 8b/10b coded and packetized pattern streams. Its analyzer recognizes disparity flips, insertions or deletions of align/skip characters that occur in USB3.0 devices using retimed loopback.

USB 3.0 Receiver Test Software

The Agilent receiver test software N5990A option 102 covers both, USB 2.0 and USB 3.0. It complements the U7243A compliance test suite with the receiver compliance, jitter tolerance, sensitivity and constant parameter stress tests. For USB 3.0 receiver testing N5990A option 102 is used in conjunction with an Agilent J-BERT N4903A/B and additional instruments. N5990A option 202 is the interface to the N5416B USB transmitter test application, providing a consolidated test report.

Integrated Protocol Analysis Solution with N5990A

The development of USB 3.0 SuperSpeed devices also requires automated test tools for characterization and compliance/pre-compliance testing at a 10x higher speed class compared to USB 2.0. Physical layer compliance testing is becoming mandatory for both the transmitter and the receiver side of the devices. Protocol testing capabilities are not only relevant to system integrators, but will also ease the physical layer testing with protocol aware error counting, like frame error rate (FER) counting. Based on Ellisys leading USB 3.0 protocol testing capabilities and Agilent’s strong physical layer offerings (J-BERT N4903B, oscilloscopes, N5990A Test Automation Software Platform for physical layer test automation) an integrated, fully automated receiver (Rx) test solution will allow USB 3.0 device developers to characterize their devices faster and by monitoring meaningful quality metrics beyond the device’s built-in error counter.

N1930B Physical Layer Test System

The Physical Layer Test System (PLTS) is the world’s leading test gear for gigabit interconnect analysis. It consists of software and hardware that create a powerful stimulus/response analysis in both time domain and frequency domain. Employing either a Vector Network Analyzer (VNA) or Time Domain Reflectometer (TDR), the PLTS system offers the most complete interconnect characterization possible, including single-ended and differential, time and frequency, reflection and transmission measurements. This tool set also includes eye diagram analysis, RLCG analysis and a vast array of fixture de-embed methodologies. Measurements based on S-Parameters can be a powerful tool to describe the measured electrical properties of the USB interconnect and by manipulating the information into various formats, can almost at a glance provide a first order estimate of the source of the design limitation. PLTS has a complete array of interconnect test methodologies built in for USB compliance and verification measurements.

Agilent E5071C Network Analyzer for Measuring and Analyzing USB 3.0 Cable and Connectors

Agilent E5071C network analyzer provides a one-box solution for cable and connector measurements according to the compliance test standard. The outstanding frequency domain analysis is the best solution for cable and connector Insertion Loss and Crosstalk. With option 010, E5071C also achieves time domain analysis such as cable and connector impedance and intra-pair skew measurements. All the measurements are supported by accurate calibration by the TRL/M method. Method of Implementation (MOI) and an automation program will be available.

Agilent 86100C DCA-J TDR probe kit for making differential time-domain reflectometry (TDR) and time-domain transition (TDT) measurements

TDR/TDT analyses are commonly performed by signal-integrity engineers during the design and validation of high-speed serial links and components. TDR/TDT measurements are also invaluable for maintaining consistent quality in printed circuit board and passive-component manufacturing. The Agilent N1021B 18-GHz differential TDR probe kit connects printed circuit boards and other devices without connectors to the 54754A differential TDR/TDT module in the 86100C Infiniium DCA-J wideband oscilloscope mainframe. In conjunction with these hardware components, engineers can use the optional 86100C-202 enhanced impedance and S-parameter software to accurately characterize differential impedances in the time and frequency domains (for example, reflections and impedances versus time or distance, or magnitude/phase/group delay of S-parameters like SDD11/SDD21).

Agilent ADS Design

USB signal integrity engineers get the right answers fast with ADS
Advanced Design System (ADS) is a powerful electronic design automation software system. It offers complete design integration to designers of products such as cellular and portable phones, pagers, wireless networks, radar and satellite communications systems, and high-speed digital serial links. It is the industry leader in high-frequency design and supports system and RF design engineers developing all types of RF designs, from simple to the most complex, from RF/microwave modules to integrated MMICs for communications and aerospace/defense applications. With a complete set of simulation technologies ranging from frequency-, time-, numeric and physical domain simulation to electromagnetic field simulation, ADS lets designers fully characterize and optimize designs. The single, integrated design environment provides system, circuit, and electromagnetic simulators, along with schematic capture, layout, and verification capability -- eliminating the stops and starts associated with changing design tools in mid-cycle.

Agilent's solutions for digital applications are driven and supported by Agilent experts who are involved in various international standard committees. We call it the Agilent Digital Test Standards Program. Our experts are active in the Joint Electronic Devices Engineering Council (JEDEC), PCI Special Interest Group (PCI-SIG®), Video Electronics Standards Association (VESA), Serial ATA International Organization (SATA-IO), Serial Attached SCSI (T10), USB-Implementers Forum (USB-IF), Mobile Industry Processor Interface (MIPI) Alliance, Ethernet standards (IEEE 802.3), Optical Internetworking Forum (OIF), and many others. Our involvement in these standards groups and their related workshops, plugfests, and seminars enables Agilent to bring the right solutions to the market when our customers need them.

Agilent's involvement in these standards gives Agilent and its customers, the computing and communication component vendors to the electronics consumer market, two main advantages:

• First, it enables us to bring the right products to the market when our customers need them. We aim to be first to market with our solutions so our customers can be first to market with their products ensuring standard compliance.
• Second, with Agilent's involvement in plug-fests, workshops and seminars we are in the unique position to develop solutions that evolve with the standards, giving the ability to design the best products with the highest confidence.

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