Enrich your test capabilities with probes and software

Today’s high-end test equipment has reached an astonishing level of capabilities. Take LeCroy’s latest LabMaster 10Zi series oscilloscopes with up to 60 GHz of real-time bandwidth and Agilent’s Infiniium 90000X series with up to 32 GHz of bandwidth. These instruments can provide a plethora of measurement capabilities for the test bench. They can reveal every detail of signals with lightning-fast rise and fall times.

But the power of these oscilloscopes would be lost without an equally powerful probing system. The last tool a test engineer needs is a probe that will affect the test engineer’s measurements or not provide the full bandwidth that the oscilloscope provides to the test engineer.

Fortunately, today’s high-end probes are designed to avoid these issues. Not only do the probes run the functions of these test equipment, but the software can also add functions and other accessories.

Increasing Probing Bandwidth

Here, take Agilent’s Infiniium 90000X series oscilloscopes as an example. The InfiniiMax III (N2800A-N2803A) is the company’s third-generation InfiniiMax high-performance probing system (Figure 1). Agilent offers four probe amplifier models with bandwidths ranging from 16 to 30 GHz. The various probes support connections using browsers, zero-insertion-force (ZIF) probe heads, 2.92-mm or 3.5-mm surface-mount (SMA) cables, or solder-in probe heads.

Agilent InfiniiMax III probe amplifiers include a ZIF probe head and a probe head. This probing system offers amplifiers with bandwidths between 16 and 30 GHz.

What is driving the continued increase in probe amplifier bandwidth? Engineers working with emerging wired communication standards and high-speed serial data links such as USB, SAS or PCI Express use oscilloscopes such as the Infiniium 90000X Series to capture fast single-shot events and make critical measurements such as jitter while ensuring compliance with industry standards to ensure interoperability. As data rates expand to over 10Gbps in the next few years, probe bandwidth will become a critical factor in making such high-bandwidth measurements.

Agilent uses a proprietary indium phosphide (InP) process and state-of-the-art thin-film packaging technology to achieve the performance of these probes within tight geometric constraints. The InfiniiMax III Explorer uses a "cross-shaped" blade ground system for low inductance grounding, a polycrystalline iron powder-wound coaxial probe head to reduce standing waves, and a replaceable resistor probe head with very low parasitic inductance to achieve 30GHz performance.

High-voltage requirements

Power measurement requirements in a variety of applications such as electric and hybrid vehicles, industrial applications, lighting, solar energy and computer servers are becoming increasingly challenging. These emerging power technologies require probes that can meet both high-voltage and low-voltage measurement requirements. Probes powered by a given oscilloscope are generally not suitable for equivalent high-voltage devices.

To this end, Tektronix recently launched four high-voltage probes and significantly upgraded three existing probe products to meet market requirements in terms of bandwidth, dynamic range, and input impedance characteristics. Tektronix's THDP, TMDP, and P52XXA series high-voltage probes can meet the requirements of these three main areas (Figure 2).

Figure 2: Tektronix's THDP, TMDP, and P52XXA high-voltage probes meet the market's power measurement requirements in terms of bandwidth, dynamic range, and input impedance characteristics.

On the one hand, today's power designs are adopting faster switching devices such as insulated gate bipolar transistors (IGBTs). Higher bandwidth probes such as the THDP0200 and TMDP0200 can capture signals with very fast slew rates, making it easy for design engineers to accurately measure these new designs.

On the other hand, these probes can address the shortcomings of traditional probes in terms of dynamic range, allowing design engineers to use the same probes to measure high-voltage signals and the noise and ripple components they cause. The THDP0100 has the largest dynamic range of the series and differential voltage and common mode specifications of ±6000V.

Finally, when probes are connected to a circuit, they can potentially change the behavior of the circuit and shielding issues. Tektronix's high-voltage probes minimize this problem by providing the highest resistive and lowest capacitive loading that a high-voltage probe can provide. For example, both the upgraded P5210A and the new THDP0100 can provide 40MΩ resistance and less than 2.5pF capacitive loading.

The TMDP and THDP connect to Tektronix oscilloscopes through the Tektronix Versatile Probe Interface (VPI) architecture used by most Tektronix mid-range oscilloscopes. The VPI architecture enables bidirectional intelligent communication between the oscilloscope and the probe. To maximize user safety in high-voltage applications, these probes meet EN61010-031 requirements.

Features of active probes

Engineers should use a variety of passive and active probes to get the most out of their oscilloscopes. It is not easy to determine which probe is best for a given application. However, Agilent offers a new generation of 1 to 2 GHz single-ended active probes in its N2795A/N2796A series (Figure 3).

Figure 3: Agilent’s N2795A/96A active probes provide extremely low input capacitance for ultra-lightly loaded DUTs.

The N2795A/96A is powered by the AutoProbe interface (compatible with Agilent's InfiniVision and Infiniium oscilloscopes). These probes incorporate many features needed for general-purpose high-speed probing, especially for digital system design, component design/characterization, and educational research applications.

An important feature of these probes is their 1MΩ input resistance and very low 1pF input capacitance, which supports very low loading of the device under test (DUT). This, combined with very high signal fidelity, makes these probes suitable for most of today's digital logic voltages. These probes also have wide dynamic range (±8 V) and offset range (±12 V for the N2796A and ±8 V for the N2796A).

Adapting to the Environment

Oscilloscope vendors generally prefer that users use their own probes with their oscilloscopes, but this is not always possible or even desirable. For this reason, test equipment vendors generally provide adapters so that you can use one probe with another oscilloscope.

Agilent's N2744A T2A Tektronix to Agilent probe adapter is an example (Figure 4). Engineers can use this adapter to connect Tektronix TekProbe-BNC Level 2 probes to Agilent's Infiniium and InfiniiVision oscilloscopes. The adapter provides the necessary probe power, calibration, and offset control for Tektronix probes. Engineers who already have Tektronix active probes can use them with Agilent oscilloscopes without having to purchase new probes.

Figure 4: Agilent’s N2744A T2A Tektronix to Agilent probe adapter allows you to connect a Tektronix probe to an Agilent oscilloscope.

Some situations often require measurements in hard-to-reach locations. In these cases, Agilent's N2887A 36-channel probe and N2888A 18-channel half-channel InfiniiMax soft touch probe heads can be used (Figure 5). These probes connect Agilent soft touch connectorless probes to the input connectors of Agilent InfiniiMax I and II Series probe amplifiers.

Figure 5: The N2887A Soft Touch Probe is a 36-channel device that connects Agilent's connectorless probes to the input of the probe amplifier.

These probes allow engineers to probe high-fidelity signals with bandwidths up to 4 GHz, and also support engineers in making multi-channel measurements typically required in dual data rate (DDR) memory testing and other high-speed applications where space is tight.

An engineer's toolbox should also include a current probe. The Agilent N2893A is a 100MHz, 15A ac-dc current probe with AutoProbe interface for InfiniiVision and Infiniium oscilloscopes. The probe features automatic degaussing and automatic calibration to eliminate residual magnetism and harmful DC offsets in the probe, allowing engineers to make more accurate low-level DC current measurements. The N2893A current probe also excels in accurately capturing static or steady-state currents, which is an essential feature for testing and debugging power electronics. [page]

Power Detection

Continuing the discussion of power measurement, the Anritsu MA24105A high-precision miniature stand-alone inline high-power sensor has a variety of power measurement capabilities from 350MHz to 4GHz (Figure 6). With a dynamic range of 2mW to 150W and integrated forward and reverse measurement capabilities, the MA24105A can be used by both manufacturing engineers and field engineers in a variety of commercial cellular, land mobile radio, and general military/defense RF applications.

Figure 6: Anritsu’s MA24105A high-precision miniature stand-alone inline high-power sensor features a wide range of power measurements from 350 MHz to 4 GHz

The MA24105A sensor is compatible with Anritsu's S3xxE series Site Master cable and antenna analyzers, MS271xE and MS272xB Spectrum Master handheld spectrum analyzers, MT8212E Cell Master, MT822xB BTS Master, and MS202xA/B and MS203xA VNA Masters. The sensor can also be used with the MS271xB economical benchtop spectrum analyzer.

High-precision average power measurements can be made using the MA24105A. The MA24105A has a wide dynamic range, so lower power sensors are not required, which reduces setup and test time. High accuracy is guaranteed because the calibration data is stored directly in the sensor and all required corrections are made within the sensor's microprocessor. Return loss and directivity are also optimized to maintain high accuracy.

The MA24105A's "dual channel" architecture enables true RMS measurements over the entire frequency range. This architecture, coupled with the dynamic range, enables users to measure continuous wave (CW), multi-carrier, and digitally modulated signals such as GSM/EDGE, CDMA/EV-DO, W-CDMA/HSPA+, WiMAX, and TD-SCDMA.

The forward channel includes a 4MHz bandwidth channel with peak and comparator/integrator circuits that add measurement capabilities such as peak envelope power, crest factor, complementary cumulative distribution function (CCDF), and burst average power. Another detection circuit on the reverse channel adds reverse power measurement capabilities, including reverse power, reflection coefficient, return loss, and standing wave ratio (SWR). The microcontroller and the signal conditioning circuitry, analog-to-digital converter (ADC), and power supply in the sensor integrate the MA24105A into a complete micro power meter.

The versatile MA24105A can be used in a wide variety of applications. Its excellent matching and low insertion loss make this sensor ideal for continuous power monitoring of transmitter systems and antennas. In addition, the 350MHz bottom frequency makes this sensor an excellent choice for measuring P25 and TETRA networks.

Software

Instrument vendors have been working to develop application-specific software packages to improve the situation where a given instrument is dedicated to a specific market segment. LeCroy's recent release of three such software packages for the automotive market is one example.

Automotive and chip vendors such as Broadcom and MOST's partners have become the driving force behind LeCroy's two QualiPHY (QPHY) automated conformance test software packages. Developers can use these packages to achieve lower cost, lower power, higher versatility and robust systems for entertainment and infotainment applications. In addition, LeCroy's Vehicle Bus Analyzer (VBA) test solution has been expanded to work on the WaveRunner 6 Zi, WavePro 7 Zi and WaveMaster 8 Zi oscilloscope platforms.

The QPHY software package provides automated test scripts that enable fast and reliable testing of MOST 50 ePHY and 150 oPHY signals. MOST (Media Oriented Systems Transport) is a multimedia and infotainment network standard widely used in the automotive market. These standards came into being as customer demand for devices connected to video displays and car entertainment systems has grown rapidly.

This demand has been growing tremendously over the past five years, creating more testing challenges for automotive design engineers who need to ensure that all devices on the same network (video displays; GPS navigation; audio, DVD, CD and satellite radio; Bluetooth connectivity and microphone systems) interoperate well and do not cause any interference.

Broadcom's recently released BroadR-Reach technology targets 100Mbps Ethernet connections over unshielded single twisted pair cabling. BroadR-Reach technology has been optimized for a variety of automotive applications, and the technology supports a variety of connection schemes for external devices. LeCroy's physical layer (PHY) test solution for BroadR-Reach technology includes the automated QualiPHY conformance test package QPHY-BroadR-Reach and the required test fixtures and cables.

In addition, the ubiquitous CAN, LIN and FlexRay automotive system protocols have played a key role in every existing car. LeCroy's VBA test package combines CAN, LIN and FlexRay triggers, decode and analysis solutions in one solution, and adds PHY tests for FlexRay.

The VBA solution has the unique ability to decode CAN protocol signals into symbolic (application layer) text via the automotive .dbc database file, allowing the user to view all CAN protocol stack information and additional in-circuit electronic signals that affect the CAN bus. The

additional capability of the VBA solution to extract data from the serial protocol information stream and plot that data on the oscilloscope display makes it a must-have for all automotive design engineers. This comprehensive feature set is now available on the WaveRunner 6 Zi, WavePro 7 Zi and WaveMaster 8 Zi oscilloscope platforms.

Automatic Probe Calibration

Although cable and probe losses are inherent, instrument vendors have been working hard to minimize channel losses in their probing systems. Depending on the configuration, the losses can be quite significant. Sometimes the losses are enough to cause measurement variations, resulting in inconsistent measurement results. In addition, the frequency response and phase characteristics of different probes are different, so each probe and cable must be characterized and considered to ensure the most realistic reproduction of the signal.

To ensure that users get the most out of their oscilloscopes and probes, Agilent offers PrecisionProbe software for its Infiniium 90000 X-Series and 90000A Series oscilloscopes. The software works with built-in hardware in Infiniium oscilloscopes, allowing engineers to automatically characterize and correct the response of any channel at the oscilloscope input without using any external devices. The analysis provided by PrecisionProbe software can improve measurement margins so that engineers can achieve the most accurate measurements.

Agilent's N2809A PrecisionProbe software can not only quickly correct for cable and channel insertion losses, but also correct for probing problems such as phase linearity and amplitude flatness. The software can match the frequency response and phase of every cable or probe on the circuit. It can also characterize and compensate for channel losses such as switches without adding other devices.

Agilent claims that PrecisionProbe is the first software for real-time oscilloscopes that provides comprehensive AC calibration for probes (not just DC calibration and deskew). In addition, the software is independent of externally generated S-parameter characterization files.

These files are typically generated from other instruments such as time domain reflectometers or vector network analyzers, which can be time-consuming to set up and require expertise to produce accurate and consistent results. PrecisionProbe uses the built-in signal source on the oscilloscope to automatically generate files. The software setup wizard quickly guides engineers through the entire setup and characterization process of channel units such as probes, cables, and switches using PrecisionProbe. (end)