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In This Issue - October 1994 Volume 45 Issue 5

CURRENT ISSUE - October 1994 Volume 45 Issue 5

Most HP test and measurement products are developed to satisfy the needs of a relatively wide range of applications. In contrast, the motivation for the development of the HP HD2000 data acquisition system (page 6) came from the highly specific needs of customers engaged in turbine and piston engine testing. The bulk of HP HD2000 measurements are made on analog inputs, 90% of them repre senting temperatures and pressures. The two main modules of the system are a 64-channel scanning analog-to-digital converter (ADC) and a pressure scanning ADC. The 64-channel scanning ADC design was a challenge because 64 channels of user-conf igurable signal conditioning circuitry had to fit on a single VXIbus C-size module, basically one large printed circuit board. The solution, as revealed in the article on page 9, is a set of plug-on signal conditioning boards that ride on the main board. Discussions of the ADC function, a special algorithm for converting voltages to temperatures and pressures, the module's built-in self- test and calibration, and the production test strategy can be found in the articles on pages 16, 21, 25, and 30, respectively. The design of the pressure scanning ADC is the subject of the article on page 35. Because HP had no expertise in pressure measurements, the design was done in partnership with a company experienced in that field.

Pressed by the need to reduce costs and increase functionality, systems designers use advanced integrated circuit technologies to create large-scale integrated (LSI) circuits that perform a multitude of analog and digital functions and have extremely high pin counts. LSI test system designers, forced to keep a step ahead, use the same strategy. Two custom ICs give the HP 9493 mixed-signal LSI test system higher pin-count capability and more functionality than its preoctessors without increasing its space requirements. One IC provides all of the pin electronics for a single pin of an IC under test. Called PBOC, for pin board on a chip, it contains a high-speed digital driver, an active load, a window comparator, a parametric tester for setting a voltage and measuring current, and control circuitry. It's the subject of the article on page 42. The second custom IC, described in the article on page 51, contains delay and formatting circuitry for the timing vector generators that generate and capture digital waveforms at the digital pins of the IC under test. Unusual because it's implemented in CMOS rather than the more conventional, higher-cost, higher-power-consumption bipolar ECL, this IC provides timing resolution of 62.5 picoseconds. The HP 9493's processing power is distributed throughout its subsystems in the form of precisely synchronized digital signal processing modules. As explained in the article on page 59, this architecture offers faster operation, better test coverage, and lower memory requirements. It also opens up a new range of applications in the area of complex signal analysis. The article on page 64 tells how the HP 9493 system can be used to measure vector error, an important parameter in modern telecommunications systems that use differential quadrature phase shift keying modulation.

You can use a vector network analyzer to measure impedances at radio frequencie s (RF) if the impedance is near 50 ohms, the most common impedance in systems operating at these frequencies. However, passive chip components and other passive surface mount devices often have very small inductances and capacitances and their impedances at RF can be much greater or much less than 50 ohms. The HP 4291A RF impedance analyzer (page 67) is designed to measure the impedances of passive surface mount devices over a frequency range of one megahertz to 1.8 gigahertz. A current-voltage measurement technique, special built-in calibr ation and compensation routines, and custom test fixtures provide accurate measuremen ts over a wide impedance range.

A frequent cause of semiconductor device death is electrical overstress (EOS). EOS can take many forms, including electrostatic discharge (ESD), electromagnet ic pulses, system transients, and lightning. The article on page 106 describes an EOS test system that is being used in the development of CMOS processes with built-in ESD and EOS robustness. The test system subjects devices to const ant-current pulses. EOS phenomena are characterized by high levels of heat and electric fields and cause failures that can be categorized as either thermally induced or electric field induced, respectively. For thermally induced failures, failure thresholds for any stress waveform can theoretically be derived from the constant-current pulse stress thresholds.

As Martin Dubuc tells us in the article on page 83, "The frame relay protocol is a data transfer protocol defined by the American National Standards Institute (ANSI) and the International Telecommunications Union (ITU). It is similar to the ISDN (Integrated Services Digital Network) standard but it assumes a reliable transmission medium and therefore contains very little error recovery functionality. As a result, it is more straightforward and data transfer is more efficient." With any standard there is a need for conformance testing to make sure that any manufacturer's products comply with the standard. Abstrac t frame relay conformance tests are developed by the Frame Relay Users Forum. These must be converted to executable test suites that will run on a specific test platform such as a protocol analyzer. The article discusses the conversion of abstract test suites to executable test suites for the HP PT502 protocol analyzer using a specially developed translator that automates what was previou sly a repetitive and error-prone process.

The Fiber Distributed Data Interface (FDDI) networking standard can be considered a descendant of earlier technologies such as Ethernet and token-ring. FDDI networks offer high-speed data transfer and fault-tolerant dual-ring topology, but can be difficult to troubleshoot because in the event of a fault the ring may simply alter its topology and keep operating so the fault is not immediately apparent. A great deal of information is available in an FDDI network for troubleshooting faults and other problems such as interoperability issues between products from different manufacturers, but it can be time-consuming or inconvenient to access that information. The FDDI Ring Manager, an application for the HP Network Advisor protocol analyzer, is designed to sift through mountains of FDDI network information and present the relevant facts to the user in a logically ordered display (see page 88). The core of the application is the ring mapper page 88). The core of the application is the ring mapper module (page 97), which provides the user with logical and physical maps of the network. The maps serve as a framework for gathering and maintaining connection, configuration, operational, and historical information for the devices on the ring. The ring mapper uses sophisticated algorithms that are designed to handle many typical difficult-to-analyze situations.

For network users, a high quality of service means a low error rate and high uptime. For network operators, this means continuously monitoring the network's performance, switching to backup links when necessary, and fixing problems quickly. The challenge is to maintain quality while keeping maintenance costs down, which means keeping the maintenance staff as small as possible and minimizing travel to remote sites. To help network operators meet these conflicting requir ements, network performance analyzers made by HP's Queensferry Telecommunications Opera tion are now available with virtual remote capability (see page 75). From a single central office, capability (see page 75). From a single central office, maintenance personnel can use an HP workstation or PC to control several remote instruments simultaneously, using a mouse. Accurate representati ons of the instruments' front panels on the PC or workstation display instantly reflect what the remote instruments are doing. The virtual remote software is completely generic, getting all of its instrument-specific information from the remote instruments themselves.

R.P. Dolan,

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