hundred megabits per second to handle telephone conversations between the cities of San Francisco and New York. Today a capacity of 2.5 gigabits per second is required to carry all the voice, data, fax, and video traffic between these two cities. Even more bandwidth (e.g., 100 Gbits/s) will be needed in the next several years).

This growth has brought about a change from copper or microwave transmission media to fiber optic systems. The advantages of optical fiber over copper are an extremely high bandwidth, low loss, high immunity to interference, and virtually no crosstalk between channels.

To ensure compatibility between manufacturers of fiber optic equipment , two primary fiber optic standards have emerged: SONET (Synchronous Optical Network) and SDH (Synchronous Digital Hierarchy). SONET is primarily a North American standard and SDH is used by the rest of the world. These standards place strict limits on the performance of each element in a fiber optic system. The HP 83480 digital communications analyzer (Article 1) is designed to verify that optical waveforms in a fiber optic system meet the requirements of the SONET and SDH standards. This instrument is the first commercial product to combine in a single package a SONET calibrated reference receiver with an oscilloscope and communications firmware.

The communications firmware in the HP 83480 (Article 2) is an extensive set of built-in measurements designed for telecommunications applications. The measurements provided by these internal firmware measurement algorithms fall into three general categories: parametric measurements (e.g., rise time, fall time, overshoot, etc.), mask measurements, which compare the shape of a waveform to a predefined mask, and eye measurements, which measure properties of eye diagrams.

The optical receiver design for the HP 83480 (Article 3) allows customers to select optical-to-electrical plug-in modules with specific transmission rates for different applications. The current optical plug-in modules provide data rates of 155/622 Mbits/s, 2.488 Gbits/s, and 9.953 Gbits/s. These data rates are multiples of 51.84 Mbits/s as required by the SONET and SDH standards.

Many of the latest designs of high-speed systems use differential transmission lines to reduce discontinuities in the signal path and reduce coupling between different signal paths. A tool that simplifies the task of analyzing the signal paths of differential transmission lines is differential TDR (time-domain reflectometry). Article 4 describes the HP 54754A differential TDR plug-in, which when used in conjunction with the HP 54750 digital oscilloscope or the HP 83480 analyzer, significantly improves the speed and ease of making critical measurements of high-speed transmission systems.

The final HP 83480 article (Article 5) discusses the problem of accurately measuring the frequency response of the communication analyzer's plug-in modules. It has typically been extremely difficult to characterize the SONET/SDH standard receiver with tolerances of +0.3 dB. This is because of inaccurate knowledge of the optical stimulus and large uncertainties in the microwave power measurement. The article describes a method for calibrating photoreceiver frequency response that overcomes these inaccuracies and uncertainties.

Increases in silicon density have made it possible to reduce chip core sizes. However, a concomitant reduction in I/O pad pitch (the repeat distance between adjacent I/O pads) has been hard to achieve because of packaging and assembly problems. Thus, IC designs that are I/O intensive tend to have a die size that is significantly greater then the core size. Articles 6 and 7 describe a technique called radially staggered bonding for dealing with this problem. The first article describes the configuration of radially staggered bonds on a die, and the second article describes an implementation of the pad circuitry for radially staggered bond pads.

Miniaturization of technology is not just confined to ICs. It is also occurring in motors and shaft encoders (sensors that measure the position of a rotating shaft). Article 8 describes the HP HEDR-8000 Series reflective optical surface mount encoders. Because of their small size and low cost, customers can design these encoders into applications such as feedback sensing for the miniature motors used in copiers, cameras, card readers, and printers.

Today, we have several handheld utilities that can tell us where we are geographically, and in some cases, where we need to go. These utilities are based on the U.S. Department of Defense Global Positioning System (GPS). GPS uses known positions of satellites in space to determine unknown positions on land, on the sea, in the air, and in space. It is a passive system in which each satellite transmits its position and the time of the position message. Some GPS equipment vendors tout GPS as the next great utility, like the power and telephone utilities. Like these utilities, GPS has a number of inherent problems that limit its use as a source of timing. Article 9 describes a technique called HP SmartClock, a collection of software algorithms that have been incorporated into HP's GPS instruments to solve or minimize these timing accuracy problems.

The next group of articles (beginning with Article 10) describe HP's third-generation ATM (Asynchronous Transfer Mode) test equipment, the HP E5200A broadband service analyzer. The test capabilities of the HP 5200A enables users to determine the health of a network at all layers of the ATM protocol stack, from the physical layer right through to the AAL (ATM adaptation layer) and above. To ensure that the E5200A meets the needs of its intended customers (i.e., installers and maintainers of large telecommunications networks that employ broadband ISDN), engineers at HP's Australian Telecommunications Operation (ATO) adopted a method called "usable usability." Usable usability (Article 14) focuses not only on achieving ease of use for potential customers, but also on the usability culture of the product development organization.

Managed objects in the context of networks are software objects that represent the capabilities and behavior of network elements such routers and switches. In the HP E5200A, managed objects play an important role in the software architecture (Article 11). Typically used to control remote network elements, managed objects are used internally by the service analyzer's application to control application objects.

A cultural shift for ATO was in the production and manufacture of the service analyzer (Article 12). ATO had to change quickly from a custom test instrument developer to an operation that produces products in higher volumes at lower costs. The article also discusses the cultural and technological obstacles that had be overcome to transition to an operation focused on design for manufacturability.

Because of the density of the printed circuit assembly for the HP E5200A, testing by conventional bed-of-nails in-circuit techniques alone was not enough. Also, because of the high cost of this printed circuit assembly, it was necessary to be able to identify defects accurately and quickly. To overcome these challenges, ATO implemented a comprehensive test strategy that included boundary scan testing and built-in self-test, supplemented by conventional testing techniques (Article 13). This strategy included eight discrete levels of testing in which each level verified a basic functionality.

C.L. Leath
Managing Editor