Triggering on mixed signal oscilloscopes

In purchasing a Mixed Signal Oscilloscope (MSO), users will have to carefully consider its triggering capabilities.

MSOs with more acquisition channels offer more triggering capabilities that will enable users to zero-in on specific digital/analog I/O signal interaction. Although its triggering capabilities still cannot compare with that of high-performance logic analyzer, triggering using MSO goes far beyond the triggering delivered by traditional four- or two-channel oscilloscopes.

Nowadays, most mixed-signal solutions and MSOs can trigger on at least a level of parallel trigger conditions, while some offer up to two levels of pattern sequence triggering with reset conditions. However, even when using relatively simple one-level pattern triggering, users will note significant differences in triggering capabilities among various mixed-signal measurement solutions/MSOs.

In choosing the right MSO, users should select one that can trigger on a combination of digital and analog inputs. Due to signal skew between logic and analog channels, some loosely tethered mixed-signal measurement solutions can only reliably trigger on one side of the acquisition system. This implies that users are allowed to trigger on a single trigger condition only — the traditional analog trigger condition or on the parallel digital condition only, but never on both. Aside from mixed-signal triggering capabilities, MSOs should also provide precise time-alignment triggering among digital channels and analog channels.

In addition, users should also consider whether the pattern triggering of the MSO includes any type of time qualification. The MSO should not only offer entry and/or exit trigger qualification, its pattern trigger conditions should also feature a minimum time-qualification condition.

Users should also keep in mind the importance of minimum time qualification in order to avoid triggering on unstable/transitional conditions. Although switching may be almost simultaneous whenever parallel digital signals change states, it is not exactly simultaneous. Slight delays may still be observed in between signals even in the best-designed systems, in addition to falling edge and limited rising speeds when signals are neither low nor high. Hence, users should not be surprised if transitional/unstable signal conditions may be seen in the system during switching of signals, even if they would want their MSO to be free of these unstable conditions.

Compared to logic analyzers, which use sample-based triggering, oscilloscopes (MSOs included) can accurately trigger at analog trigger level/threshold crossing points.

Sample-based triggering means the device randomly samples the input signal first. Based on the sampled data, it then establishes the trigger reference point. Although this type of triggering may be adequate for typical logic analyzer measurements, it is not acceptable for traditional oscilloscope measurements, much less to an MSO, for viewing repetitive signals.

Finally, when evaluating MSOs, users should consider whether or not the oscilloscope can trigger on a certain address as well as data transmissions of serial I/O, which is very prevalent nowadays in embedded designs, like SPI and I2C.

Typical measurement applications of Mixed Signal Oscilloscopes

Aside from capturing digital and analog signals on mixed signal devices, the primary measurement application of mixed-signal oscilloscopes (MSO) involve verifying and debugging microcontrollers (MCU)/digital signal processors (DSP)-based mixed-signal with data buses and embedded address.

Generally, today’s MSOs offer 16 channels of digital acquisition, leading to the mistaken assumption by engineers that MSOs are limited to eight-bit processing applications. It has to be noted that MSOs are used primarily to monitor digital and analog I/O, which consist of all the signals available in DSP- and MCU-based designs. Moreover, users should not get into the habit of relating the MSO’s number of digital channels of acquisition with the number of bits of processing within an internal bus-based DSP or MCU, as it is usually irrelevant. Having sixteen digital channels and two to four analog channels is more than adequate for users to verify and monitor dedicated/specific functions of eight-bit, 16-bit or even 32-bit DSP/MCU-based designs.

Monitoring data lines and parallel address in an external bus-based design, like a 32-bit microprocessor computer, is not the MSO’s primary measurement application. This could be best addressed with a logic analyzer. In addition, if users need to simultaneously time-correlate analog signals and/or analog characteristics of digital signals, multiple vendors offer a two-box solution of oscilloscope and logic analyzer. With this type of solution, users must accept the logic analyzer’s more complex use-model including its single-shot or slow waveform update rates.

An MSO offering 16-logic channels with two to four analog channels is enough to measure critical timing parameters even in 32-bit systems that feature external memory devices.

The MSO’s digital and analog acquisition performance is more important than the number of channels. The most basic specifications of the analog acquisition performance of the oscilloscope are sample rate and bandwidth.

The bandwidth of the oscilloscope should be approximately five times higher than its system’s highest clock rate. For singleshot/real-time measurements, the sample rate of the oscilloscope should be at least four times more than its bandwidth, or faster.

However, some logic analyzer and oscilloscope users do not fully understand the required acquisition performance of logic analyzers and MSOs. The digital acquisition performance of an MSO should be commensurate with its analog acquisition performance, and combining a low-performance logic analyzer with a high-performance oscilloscope does not make sense.

When using digital/logic acquisition channels, the measurement resolution of the device is restricted to plus or minus one sample period. Thus, if a user attempts to capture digital signals with up to 200 MHz toggle/clock rate, each of its high or low pulse could be as narrow as 2.5 ns. This implies that if the digital acquisition system of the MSO samples at up to two GSa/s, the timing measurements per edge of the pulse could be in error by ±500 ps, which translates to 40 percent error on a 2.5 ns pulse. This explains why digital channel acquisition sample rates must be at least twice the oscilloscope’s bandwidth or higher.

Another important specification of an MSO is probing bandwidth, which includes both the digital and analog system probing.

Mixed Signal Oscilloscope Explained

An MSO (mixed signal oscilloscope) is a hybrid test device that seamlessly combines some of the measurement capabilities found in a logic analyzer with the measurement capabilities found in a DSO (digital storage oscilloscope), such as trigger holdoff, autoscale, probe/channel de-skew and infinitepersistence on digital and analog channels — in one compact instrument. An MSO allows users to view multiple time-aligned digital and analog waveforms on a single display.

Compared to a full-fledged logic analyzer, an MSO does not have large number of digital acquisition channels. It also lacks most of the advanced digital measurement functions offered by logic analyzers. Despite this, an MSO still offers some unique advantages over both logic analyzers and traditional oscilloscopes.

One of its primary advantages is its use model. An MSO can be used in almost the same manner that users use an oscilloscope. Because of the complexity and time needed to learn or relearn a logic analyzer, design and test engineers generally avoid using one. Another reason why engineers avoid a logic analyzer is the much longer time needed to set one up to make measurements. Moreover, the logic analyzer’s advanced measurement capabilities add complexity and are commonly regarded as an overkill for most of MCU- (microcontrollers) and DSP-based (digital signal processors) designs.

As one of R&D’s most commonly utilized test instruments, embedded hardware design engineers must have a basic knowledge on how to operate an oscilloscope to achieve signal-quality and timing measurements. However, the measurements of dual-channel and four-channel oscilloscope are insufficient to test and monitor critical timing interactions between digital and analog signals. This is the time when an MSO proves to be of much help.

Since an MSO offers “just enough” logic analyzer measurement capability, minus the complexity, it is usually regarded as the appropriate tool for debugging embedded designs. With the use-model similar to that of an oscilloscope, an MSO can also be thought of as a multi-channel oscilloscope with some channels (logic/digital) offering low-resolution measurements (one bit), while several channels (analog) offers lots of vertical resolution, usually eight-bits.

Unlike a loosely-tethered two-box, mixed-signal measurement solution, a highly integrated MSO is user-friendly, delivers fast waveform update rates while operating more like an oscilloscope and not like a logic analyzer.

Waveform update is one of the important characteristics of an oscilloscope since it directly impacts the instrument’s usability. With sluggish response limiting the usability, users may find it frustrating to operate an unresponsive and slow oscilloscope. This applies not only to DSOs but to MSOs as well. Thus, oscilloscope vendors should ensure that waveform update rate is not compromised when they create an MSO by porting logic acquisition channels into a DSO. Otherwise, this would lead to sacrificing the use-model of traditional oscilloscope. Moreover, mixed-signal measurement solutions that are based on external logic pods and/or two-box solutions connected through an external communication bus like USB are generally difficult to use and unresponsive. On the other hand, MSOs that are based on highly integrated hardware architecture are easier to use and more responsive.

Tektronix Enhances Bench Oscilloscope Family

Tektronix, Inc. announced a series of new models, options and enhancements to its popular MSO/DPO4000B and MSO/DPO3000 mixed signal oscilloscope series, helping to address a broader range of embedded system test and debug needs at more aggressive price points.

With the new models and enhancements to its bench oscilloscope family, Tektronix is making it possible for engineers to avoid compromising on performance and accuracy in order to stay within tight budget constraints. While embedded designs continue to grow in complexity, budget levels in many cases have stayed constant or gone down. With these introductions, Tektronix is adding more pricing and configuration flexibility to help engineers configure affordable test solutions to meet their needs.

Six new MSO/DPO4000B oscilloscope models

With high-speed buses like USB 2.0 and Ethernet now being implemented in mainstream embedded designs, faster, more capable oscilloscopes with at least 1 GHz bandwidth are becoming the norm. This in turn has created a need for more flexibility in terms of number of channels and record length at this level of performance.

To meet this need, Tektronix is introducing six new MSO/DPO4000B oscilloscopes with 1 GHz performance. The company will offer two channel models with 20 Mpoint record lengths and two and four channel “lite” versions with 5 Mpoint record length. New “lite” or “L” models such as the DPO4102B-L drop the starting price for the series to under $10,000, with further flexibility across the full product range.

All 1 GHz oscilloscopes in the MSO/DPO4000B series include one TPP1000 1 GHz passive probe per analog channel. This general-purpose probe features extremely low 3.9 pF capacitive loading for visibility into the high-frequency signal details found in USB 2.0 and Ethernet devices. In contrast, competitive 1 GHz oscilloscopes typically come with 500 MHz probes, requiring additional investment for testing higher-speed signals.

Bandwidth upgrades for MSO/DPO3000, more serial bus support

Project requirements can change over time, creating a need for improved oscilloscope performance. With the addition of new bandwidth upgrade products for the MSO/DPO3000 series oscilloscopes, engineers can purchase the bandwidth they need now, and simply upgrade it (up to 500MHz) when project requirements change – without purchasing a whole new instrument. These oscilloscopes are ideal for general purpose debug, power analysis or serial and parallel bus analysis.

In addition to bandwidth upgrades, the MSO/DPO3000 series oscilloscopes now offer comprehensive support for MIL-STD-1553 and FlexRay serial buses popular in the aerospace and automotive industries respectively. Both the DPO3AERO and DPO3FLEX modules enable triggering on packet-level information as well as analytical tools such as digital views of the signals, bus views, packet decoding, search tools, and packet decode tables with time-stamp information. Further broadening the range of serial bus support that includes I2C, SPI, CAN, LIN, RS232/422/485/UART and I2S/LJ/RJ/TDM.

Tektronix bench oscilloscopes

Tektronix bench oscilloscopes deliver innovative features to help engineers complete debug and analysis jobs quickly and efficiently. These oscilloscopes are delivered with probes reducing total purchase price. They offer extensive triggers to identify elusive anomalies and comprehensive Wave Inspector tools to navigate waveforms and track down signal problems.

Tektronix, Inc.
www.tektronix.com

PicoScope 2205 Mixed-Signal Oscilloscope

Pico Technology (www.picotech.com) has released a dual channel Mixed-Signal Oscilloscope (MSO) that allows users to simultaneously measure both digital and analogue signals and view the digital data and analogue waveforms on the screen.

The 25 MHz PicoScope 2205 MSO offers 16 digital channels, a mixed signal sampling rate of 200 MS/s, a buffer memory of 48 kS and a vertical resolution of eight bits, making it ideally suited for circuit design as well as testing and troubleshooting.

It offers five professional instruments — a logic analyzer, function generator, oscilloscope, arbitrary waveform generator and a function generator — in a single compact package.

PicoScope 2205 MSO offers maths and reference channels, mask limit testing, serial decoding, advanced digital triggering, color persistence display and automatic measurements.

The USB-powered, full-featured oscilloscope has 16 digital inputs that can be individually displayed or in arbitrary groups labeled with decimal, hexadecimal or binary values. A logic threshold ranging between -5 V and +5 V can be defined for every eight-bit input port. A bit pattern and an optional transition on the input can activate the digital trigger, while advanced logic triggers can be set on the digital or analog input channels or both, enabling complex mixed-signal triggering.

The compact, USB–powered design of the oscilloscope implies that it can be used both in the field and on the desktop. Its ability to be used as a function generator, spectrum analyzer and arbitrary waveform generator makes it a complete test and measurement lab.

Saelig Introduces Tiny DIP Oscilloscope Module

Saelig Company, Inc. (www.saelig.com) has introduced Xminilab – a sophisticated miniature combination of three electronic instruments: a mixed signal oscilloscope, an arbitrary waveform generator, and a protocol sniffer. Measuring only 3.3” x 1.75”, it can be mounted directly on a breadboard or pcb for in situ testing and verification. A graphic 2.4” 128×64 pixel OLED display is mounted on the board, displaying the monitored signals with automatic measurements, adjustable persistence, cursors, and grids. The two analog channels can be added, multiplied, inverted, or averaged. Based on Atmel’s ATXMEGA32A4 microcontroller, with 32KB Flash, 4KB SRAM, 1KB EEPROM, Xminilab can also be used as a development board for the AVR’s XMEGA microcontroller.

As a Mixed Signal Oscilloscope, Xminilab offers simultaneous 2MSa/s sampling of 2 analog signals (d.c. to 200kHz) as well as 8 digital lines. Advanced Trigger options include: Normal / Single / Auto / Free, with edge or slope types, rising or falling; adjustable trigger level, and the ability to view signals prior to the trigger. VDC, VPP and frequency can all be displayed too. Xminilab even features an XY Mode for plotting Lissajous figures, V/I curves or for checking the phase difference between two waveforms.

A FFT Spectrum Analyzer offers different windowing options and selectable vertical logarithmic display for signals up to 200kHz, with FFT spectrum frequency plotted as vs. magnitude for each analog channel.

A ±2V 8-bit Arbitrary Waveform Generator with frequency sweep generates signals up to 44kHz. Arbitrary Waveform Generator offers ±2V Sine, Triangle, and Square waves, with control of amplitude, frequency, offset and duty cycle. Xminilab’s Sweep feature increases the frequency of the wave automatically on each screen refresh of the oscilloscope. Since the sweep is synchronized with the oscilloscope, displaying perfect frequency plots is easy.

Protocol Decoding and Sniffing is provided for SPI, I2C, UART, as well as Parallel Decoding, which shows hexadecimal values of the 8 bit digital input lines.

Four onboard tactile switches are provided for function control, and Xminilab can be powered either via external +5V or via the micro-USB connector, which also enables future enhancements.

Saelig Company Inc.
www.saelig.com

First iPhone- based Mixed Signal Oscilloscope unveiled

Saelig Company, Inc. (www.saelig.com) has unveiled the first mixed-signal oscilloscope in the world that moves Apple’s ubiquitous touch-screen interface and iOS devices into the test and measurement world — the iMSO-104.

This revolutionary oscilloscope is an adapter for iPhone, iPod touch and iPad that is easy to use, making it suitable for field service, application and sales engineers as well as hobbyists and students.

With a maximum sampling rate of 12 MSa/s and five MHz bandwidth, iMSO-104 can simultaneously analyze four digital and one analog signals for time-synchronized and versatile troubleshooting. It offers all the usual trigger, input and math features found in high quality oscilloscope, including variable persistence, cursor measurements and integrated 3.3V 1 kHz reference signal.

The oscilloscope also has novel features such as instant emailing of screen captures and computation power. Moreover, simple measurements of period, frequency, reference signal capture and duty cycle are just a touch away. With input voltage display ranging from 50 mV to 2 V/div, the oscilloscope’s timebase range between 2uS and 1S/div.

It is based on Cypress Semiconductor’s PSoC 3, which is a low power, system-on-a-chip mixed-signal IC that handles the proprietary dock interface of Apple for iOS devices while processing incoming digital and analog signals simultaneously. This results to a handy intuitive oscilloscope system that is extremely portable and affordable. It uses intuitive finger movements to adjust trigger level, repositioning channel displays or zooming. Captured signal screenshots can be sent rapidly as a time-saving email image for quick reporting, Sent through other available Apps. In addition, time and current location can be incorporated in the email with a link to Google Maps for distinct logging on-the-job signal information.

Yokogawa DL9710L Mixed Signal Oscilloscope

Yokogawa Electric (www.yokogawa.com) has unveiled a four channel oscilloscope that is designed to match sample rate and memory depth between the logic and analog channels — the DL9710L mixed signal oscilloscope.

Offering bandwidth of 1GHz, the oscilloscope features a memory length of 6.25 MW/ch and a maximum real-time sampling rate of five GS/s. This lightweight and compact oscilloscope also comes with versatile search and zoom functions.

Unlike other oscilloscopes which show digitally persisted acquisitions in a single display layer, the DL9710L allows users to toggle digital persistence on or off, and with the oscilloscope’s unique “history memory” function users can separate and observe previously acquired data individually.

Aside from updating the display at high speed, the oscilloscope also offers a function for recalling a maximum of 2000 screens worth of past waveforms.

In addition, to take full advantage of the oscilloscope’s full potential; the oscilloscope should not only offer high-speed screen updating. It should also have the ability to analyze and redisplay individual waveforms.

The DL9710L mixed signal oscilloscope permits users to assign 32-bit logic signals to a maximum of five groups. The number of bits assigned for each group is unlimited. Thus, all 32 bits can be assigned to a single group.

For easy and flexible settings, groups are divided using a graphical interface, while analysis such as state display, DA conversion and bus display can be executed on a group-by-group basis.

Featuring a variety of waveform search functions, the DL9710L MSO enables users to find specific serial or parallel data patterns or detect abnormal signals. Its data search types include state search, zone search, serial pattern search, waveform parameter search and waveform window search.

Tektronix “2-box” solution revealed

Tektronix (www.tek.com) has unveiled industry’s only-customer proven and most cost-effective solution for the MIPI Alliance M-PHY testing anchored on the new M-PHY v1.0 specification.

Unlike competitive offerings for M-PHY test that demands a vast array of instruments to cover the entire range of M-PHY test mandates, the Tektronix “2-box” solution requires only an AWG7000 Series arbitrary waveform generator and a DPO/DSA/MSO70000 series oscilloscope.

With just a single set-up for both the lower-speed D-PHY and M-PHY, the solution offers a scope-integrated error detection for receiver reusability and tolerance testing.

“We worked closely with Tektronix to test our high-quality DesignWare MIPI M-PHY solution, giving designers further confidence that the IP is robust and fully compliant to the latest M-PHY v 1.0 specification,” explained Navraj Nandra, Senior Director of Marketing for Mixed-Signal and Analog IP at Synopsys.

“Synopsys used the Tektronix DPO70804 and DSA8200 oscilloscopes to help ensure that the silicon-proven DesignWare MIPI M-PHY met the necessary electrical characteristics and performance requirements.”

A high-speed serial interface to the UniPro, DigRF v4, CSI-3, LLI and MIPI Alliance’s DSI-2 interconnect standards, the M-PHY will be utilized in the development of mobile devices that provide effective power management schemes, increased performance, low RF emission and robustness against RF interferences.

The “2-box” solution covers both Receiver and Transmitter tests, including Error-Detection, comprehensive high-speed tests, Pulse Width Modulation (PWM) signaling, DigRF verification and PSD (Power Spectral Density) measurements.

Option transforms Rohde & Schwarz RTO oscilloscopes into MSO

Rohde & Schwarz (www2.rohde-schwarz.com) has unveiled its latest mixed-signal oscilloscope (MSO) option specifically developed for its RTO oscilloscope that offers 16 digital logic channels while utilizing the base unit for mixed-signal analysis.

Inserted into a slot of the instrument’s rear, the hardware option transforms the instrument into an MSO. This allows the oscilloscope to provide not only two or four analog channels, but 16 digital logic channels as well, with 400 MHz input frequency, while time correlation is offered between the analog and digital sections of the oscilloscope.

The company’s RTO with MSO functionality features a sampling rate of five GSa/s across the 200 Msample memory depth. A time resolution of up to 200 ps allows the oscilloscope to accurately analyze quality and signal content.

The new option comes with hardware-based trigger, acquisition and processing units. Acquisition of more than 200,000 waveforms can be easily achieved, even with the digital channels turned on. The digital trigger of the oscilloscope ensures high precision, while its various trigger types helps pinpoint errors.

Rohde & Schwarz has also included a decoding and trigger option for the FlexRay serial communications interface.

The hardware-based trigger system offers a range of protocol-specific trigger conditions and high acquisition rates, enabling the oscilloscope to deliver flexible debugging and testing approaches. Test dialogs are intuitive while explanatory links and graphics to other settings expedite configuration. Protocol data are compiled in tables while protocol details within the measured waveform are color-coded.

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