Complete testing with probe and software testing capabilities

　　Today's high-end test equipment has reached an amazing level of capabilities. For example, LeCroy's latest LabMaster 10Zi series oscilloscopes with real-time bandwidths up to 60GHz and Agilent's Infiniium 90000X series with bandwidths up to 32GHz. These instruments can provide a large number of measurement capabilities for the test bench. They can show 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 final tool a test engineer needs is a probe that will affect the test engineer's measurements and otherwise not provide the full bandwidth that the oscilloscope provides to the test engineer.

　　Fortunately, today's high-end probes are designed to avoid these problems. Not only can the probes perform the functions of these test fixtures, but software can also add functionality and other accessories.

　　Increasing detection bandwidth

　　Here, we take Agilent's Infiniium 90000X series oscilloscope as an example. InfiniiMax III (N2800A-N2803A) is the company's third-generation InfiniiMax high-performance detection system (Figure 1). Agilent offers four probe amplifier models with bandwidths between 16 and 30 GHz. 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.

Figure 1: Agilent's InfiniiMax III probe amplifier includes 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 these 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 lower inductance grounding, a polycrystalline iron powder-wound coaxial probe tip to reduce standing waves, and a replaceable resistor probe tip with very low parasitic inductance to achieve 30GHz performance.

　　High voltage requirements

　　Power measurement requirements in applications as diverse 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 handle both high and low voltage measurements. Probes that are powered by a given oscilloscope are generally not suitable for equivalent high voltage devices.

　　To this end, Tektronix has 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 supply 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 switching rates, making it easy for design engineers to accurately measure these new designs.

　　On the other hand, these probes can solve the shortcomings of traditional probes in terms of dynamic range, allowing design engineers to use the same probe to measure high-voltage signals and the noise and ripple components caused by them. The THDP0100 has the largest dynamic range of the series and a differential voltage and common mode specification of ±6000V.

　　Finally, when probes are connected to a circuit, they can potentially change the behavior of the circuit and cause shielding issues. Tektronix 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 offer 40MΩ resistance and less than 2.5pF capacitive loading.

　　The TMDP and THDP connect to the Tektronix oscilloscope via the Tektronix Versatile Probe Interface (VPI) architecture used in 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.

　　Active Probe Characteristics

　　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 required 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 ultra-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 a wide dynamic range (±8 V) and offset range (±12 V for N2796A and ±8 V for N2796A).

　　Change according 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.

　　An example is Agilent's N2744A T2A Tektronix to Agilent probe adapter (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 controls 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.

Certain situations often require measurements to be made 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. [page]

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 making multi-channel measurements typically required in double data rate (DDR) memory testing and other high-speed applications where space is tight.

　　An engineer's toolbox should also include a current probe. Agilent's 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 bias 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 current, which is essential for testing and debugging power electronics.

　　Power detection

　　Continuing with power measurement, the Anritsu MA24105A high-precision miniature stand-alone inline high-power sensor features a wide range of power measurements 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.

　　The MA24105A enables high-precision average power measurements. The MA24105A has a wide dynamic range, eliminating the need for lower-power sensors, 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 across 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. [page]

　　The forward channel contains 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, along with 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 the perfect 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 manufacturers such as Broadcom and MOST partners are now the driving force behind LeCroy's two QualiPHY (QPHY) automated conformance test packages. Developers can use these packages to achieve lower cost, lower power, higher versatility and more robust systems for entertainment and infotainment applications. In addition, LeCroy's Vehicle Bus Analyzer (VBA) test solution has been expanded to work on WaveRunner 6 Zi, WavePro 7 Zi and WaveMaster 8 Zi oscilloscope platforms.

The QPHY 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 used extensively in the automotive market. These standards were created in response to the rapid growth in customer demand for devices that connect to video displays and car entertainment systems.

　　This demand has grown tremendously over the past five years, creating additional 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 without causing 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 software 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 suite combines CAN, LIN and FlexRay triggers, decode and analysis solutions in one solution, and adds PHY testing for FlexRay.

　　The VBA solution has the unique capability to decode the 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 go to great lengths to minimize channel loss in their probing systems. Depending on the configuration, the loss can be significant. Sometimes the loss is enough to cause measurement variation, resulting in inconsistent measurement results. In addition, the frequency response and phase characteristics of different probes vary, so each probe and cable must be characterized and considered to ensure the most faithful 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 the built-in hardware in the Infiniium oscilloscope, allowing engineers to automatically characterize and correct the response of any channel of 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 cable and channel insertion loss, but also correct detection problems such as phase linearity and amplitude flatness. The software can match the frequency response and phase of each cable or probe on the circuit. It can also characterize and compensate for the loss of channels such as switches without adding other devices.

　　Agilent claims PrecisionProbe is the first software for real-time oscilloscopes to provide full AC calibration of probes (not just DC calibration and deskew) and is agnostic to externally generated S-parameter characterization files.

　　These files are usually 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.