Importance of a deep memory in oscilloscopes

Regardless of the application, an oscilloscope with deep memory offers numerous advantages that are difficult to live without. Thus, it is vital for users to understand the importance of a deep memory.

The sample rate of an oscilloscope only indicates the maximum sample rate that can be achieved. To determine the sample rate, users should know the memory depth of the oscilloscope. Given the oscilloscope’s memory depth and its typical time base settings, users can then calculate its sample rate.

Oscilloscopes stores samples into memory. The bigger the memory, the more samples can be stored, and the more samples are stored, the higher the sample rate. This implies that deeper memory allows users to sustain the oscilloscope’s maximum sample rate across a vast array of timebase settings. With the higher sustained sample rate, deeper memory also offers more reliable and accurate measurements.

One of the common challenge for oscilloscope users is how to effectively capture adequate cycles of both fast and slow signals simultaneously and maintain enough resolution to zoom in and view signal details. Insufficient resolution between points, leave users in the dark of what is really going on with their design while running the risk of completely missing events like glitches or anomalies. Without a fast deep memory oscilloscope, serious problems such as these can take hours or even days to finally discover.

Also, a shallower-memory oscilloscope compromises sample rate, providing an incomplete view of the digital and analog interaction in the design.

When signals behave badly during power up, even the most powerful triggering capability of the oscilloscope won’t solve the mystery of where to start looking for the cause. The only solution to the problem would be a deep memory, which provides users the ability to observe a full-start-up cycle with high resolution at longer periods of time. This effectively enables users to trace the path between the symptom as well as the root cause.

Deep memory also plays a critical role in analyzing the spectrum of signals. The frequency resolution is related directly to the amount of time displayed on the screen, with more time offering finer resolution. In addition, the maximum frequency that users can view is tied directly to sample rate — higher sample rate enables users to observe at a higher maximum frequency. Deep memory is required in capturing and viewing at longer periods of time and at higher resolution.

Overall, deep memory offers various things that users are looking for in an oscilloscope, such as the confidence that nothing is missed. An oscilloscope with deep memory delivers high resolution waveform capture attributed to its high sustained sample rate, the ability to trace symptoms back to its main cause when a good trigger event cannot be defined, and the ability to view at longer periods of time, which is especially useful when simultaneously viewing both digital and analog signals.

Categories of oscilloscope measurements

Digital oscilloscopes enable users to perform various types of measurements on the waveform. The range and complexity of measurements offered depend on the feature set of the oscilloscope.

Oscilloscope measurements can be divided into three different categories – the vertical-axis, horizontal axis and the frequency domain.

Analyzing the vertical component of the applied signal, vertical-axis measurements depict a signal in terms of a voltage level. They can also correspond to power, current or any other physical phenomena converted to voltage through a transducer or probe.

Some common vertical-axis measurements include peak-to-peak, amplitude and RMS voltage.

Peak-to-peak and amplitude are two vertical measurements that users are often confused with. This is because they are similar for all kinds of signals, except for pulse signal.

Peak-to-peak determines the voltage difference between the high voltage and the low voltage of a cycle on a waveform, while amplitude calculates the difference between where the pulse settles at the high voltage and low voltage of the signal.

RMS calculates the waveform’s RMS voltage, a quantity that can be utilized to compute the power.

The oscilloscope’s horizontal-axis measurements enable users to analyze the applied signal’s horizontal time axis, and include measurements such as Rise Time, Pulse Width, Period and Frequency. Although the value returned is usually expressed in time, it can also be expressed as a radian, ratio or in Hertz.

Rise time calculates the amount of time needed by a signal to travel from a low voltage to a high voltage, and is determined by computing the period of time needed to go from 10 percent to 90 percent of the peak-to-peak voltage.

A positive pulse width measurement determines the width of a pulse by calculating the time needed by the wave to go from 50 percent of the peak-to-peak to the maximum voltage and back again to the 50 percent mark. Meanwhile, a negative pulse width measurement determines the width of a pulse by measuring the time spent by the wave to go from 50 percent of the peak-to-peak to the minimum voltage and back again to the 50 percent mark.

Utilizing the entire waveform in the capture window, the period determines the average time for a cycle to complete, while the frequency function measures the frequency of the waveform.

The oscilloscope’s frequency domain measurements translate a time-domain waveform using a Fast Fourier Transform (FFT), and then measuring the frequency domain’s distortion and noise characteristics. Frequency domain measurements offer phase and magnitude characteristics versus frequency.

Aside from measurements, various mathematical operations can also be performed on the waveforms, including absolute value, subtraction or addition integration and fourier transform.

Absolute value indicates the absolute value of the waveform in terms of voltage, while subtraction or addition allows users to subtract or add multiple waveforms and show the resulting signal on the screen. Integration computes the integral of the waveform, while fourier transform allows users to view the frequencies that comprise the signal.

LeCroy WavePro 760Zi-A Oscilloscope

LeCroy (www.lecroy.com) has introduced a four channel oscilloscope that combines high bandwidth edge with 10 different SMART triggers, allowing users to quickly isolate problems and start focusing on the cause.

Offering six GHz bandwidth, the WavePro 760Zi-A comes with a large 15.4-inch WXGA color display, a sampling rate of up to 20 GS/s as well as 50 Ω and 1 MΩ input capability. The oscilloscope also include both ProLink and ProBus input types, enabling eight probes to be attached and multiplexed by remote control or from the front panel.

The WavePro 760Zi-A features TriggerScan, which employs high-speed hardware triggering capability to provide users with up to 100X faster answers while capturing only the signals of interest. Unlike conventional fast display update modes that operate best on frequent events on slow edge rates, TriggerScan works best in locating infrequent events occurring on fast edge rates.

Since the best trigger is inadequate to locate all unusual events, WaveScan offers the ability to find unusual events in just a single capture or “scan” for a particular event in various acquisitions over longer periods of time. Users can choose from over 20 search modes, such as rise time, frequency, duty cycle and runt. Whenever an event is identified, WaveScan highlights the error on the display, showing a table listing of the errors found.

The oscilloscope’s proprietary X-Stream II architecture effectively made long acquisition memory seamless and easy, as it supports measuring, zooming, capturing and analyzing multiple waveforms at 256 Mpts deep.

New technology helps GDS-1152A oscilloscope overcome memory constraints

A 150 MHz oscilloscope from GW Instek’s (www.gwinstek.com) GDS-1000A Series overcome problems related to memory constraints with its MemoryPrime technology. The GDS-1152A is a dual channel digital oscilloscope that delivers a maximum real-time sampling rate of 1 GSa/s and an equivalent sample rate of up to 25 GSa/s.

Its integrated MemoryPrime technology enables the oscilloscope to capture up to 2 M points of waveform data. To allow engineers to take full advantage of its deep memory and to help them analyze waveforms faster, the oscilloscope also features Set Time Mark and Horizontal Page Skip functionalities.

This feature-rich oscilloscope comes with SD memory card support, high resolution, 5.6-inch color TFT display, USB remote control and user-friendly interface. It even offers a lifetime warranty program.

Its integrated Autoset function provides engineers with remarkable convenience. Since conventional auto measurement information is insufficient for modern measurement needs, the GDS-1152A features a Cursor Gating function that allows users to mark a specific area with the auto measurement’s cursor.

With PictBridge, the GDS-1152A oscilloscope enables users to print directly from printers with complex configuration.

In addition, the digital oscilloscope’s FreeWave remote monitoring software allows users to easily and conveniently save screenshots as an image file in jpg and bmp formats, log waveform data, and record movie files in real-time. The software also enables the oscilloscope to record and monitor waveforms over a longer period of time, while enabling previously recorded waveforms to be observed.

Oscilloscope Controls

Oscilloscopes are operated using the front-panel controls, which are divided into four main groups — the horizontal and vertical controls, input controls and the triggering controls.

Found in the front-panel section marked Horizontal, the horizontal controls of the oscilloscope allow users to adjust the display’s horizontal scale. This section includes the control for the horizontal delay (offset) as well as the control that indicates the time per division on the x-axis. The first control allows users to scan through a range of time, while the latter enables users to zoom in on a particular range of time by decreasing the time per division.

Meanwhile, the oscilloscope’s vertical controls are generally located in a section specifically marked Vertical. The controls found in this section allow users to adjust the display’s vertical aspect, and include the control that indicates the number of volts per division on the display grid’s y-axis. Also found in this section is the control for the waveform’s vertical offset, which translates the waveform up or down the display.

Triggering on the signal helps provide a usable and stable display and enables users to synchronize the oscilloscope’s acquisition on the waveform of interest. The trigger controls of the oscilloscope allow users to choose the vertical trigger level as well as the desired triggering capability. Common triggering types include glitch triggering, edge triggering and pulse-width triggering.

Useful for identifying random errors or glitches, glitch triggering enables users to trigger on a pulse or event whose width is less than or greater than some specified length of time. This triggering mode allows users to capture errors or glitches that do not occur very often, making them very hard to see.

The most famous triggering mode, edge triggering occurs when the voltage exceeds some set threshold value. This mode allows users to choose between triggering on a falling or rising edge.

Although pulse-width triggering is comparable to glitch triggering when users are looking for pulse width, it is, however, more general since it allows users to trigger on pulses of specified width. Users can also select the polarity of the pulses to be triggered and set the trigger’s horizontal position. This enables users to view what occurred during pre-trigger or post-trigger.

The input controls of an oscilloscope commonly comprise two or four analog channels. They are usually numbered and features a button associated with every channel that allows users to turn them on and off. This section may also include a selection that enables users to specify DC or AC coupling. Choosing the DC coupling implies that the entire signal will be input. The AC coupling, on the other hand, blocks the DC component and focuses the waveform around zero volts. Users can also specify the probe impedance of the channels through a selection button. In addition, the input controls allow users to select the type of sampling to be used.

LeCroy unveils High Resolution Oscilloscopes

LeCroy (www.lecroy.com) has proudly announced that its High Resolution Oscilloscope (HRO) models are the world’s lowest-noise and clearest oscilloscopes. Combining true 12-bit ADC’s, the oscilloscopes feature newly designed low-noise front ends that deliver unmatched signal fidelity.

LeCroy’s HRO models offer a shocking contrast to conventional eight-bit oscilloscopes as they deliver crisp, super-thin traces as well as blazing responsiveness and update speed.

In addition, the HRO family provides a powerful feature set that includes a vast array of advanced triggering options to isolate events, application packages, probing options, a user interface specifically developed for fast and easy navigation and lightning-fast performance.

The oscilloscopes’ pristine signal acquisition architecture provides unmatched signal fidelity at low noise. This is augmented by a large offset and timebase delay adjustment to enable easy amplifier performance and signal assessment and zooming on horizontal and vertical signal characteristics.

The models also feature a WavePilot control area, which offers convenient control of Decode, Cursors, History, WaveScan, Spectrum and LabNotebook through their corresponding function button on the front panel.

The oscilloscopes powerfully combine high bandwidth edge with 10 different SMART triggers, measurement trigger, four stage cascading triggering and TriggerScan, allowing users to isolate problems easily and focus on the cause.

The large, high resolution 12.1-inch WXGA screen offers the best view of all types of signal on the display. The screen can be rotated 90° to optimize the display for viewing jitter tracks, digital signals, frequency plots and eye diagrams.

New 89600 VSA software compatible with Agilent oscilloscopes

Agilent Technologies Inc. (www.agilent.com) has unveiled the latest, innovative multi-measurement capability to its 89600 VSA software. Compatible with the company’s oscilloscopes, this advanced software allows simultaneous signal analysis of numerous carriers and signal formats for deeper signal insight and more efficient testing in wireless test.

A premier vector signal analysis solution for R&D, Agilent’s 89600 VSA software offers standards-based and advanced general purpose tools for evaluating signal spectrum, time and modulation characteristics.

The multi-measurement capability of the 89600 VSA software has been specifically designed to provide the power of multiple signal analyzers featuring the convenience of an optimized, single user interface. The advanced architecture of the software allows engineers to simultaneously configure multiple measurements. And since all measurements are stored in the memory, they can be easily called on for coordinated and immediate execution.

Moreover, the new software also enables engineers to sequentially perform measurements when the signals are too far apart to be captured in one acquisition. The results are then displayed on one screen, allowing engineers to do in-depth comparison using user-defined equations and trace overlays.

“The success of our wireless customers depends heavily on their ability to keep pace with rapidly evolving technologies and standards,” remarked Guy Sene, Vice President and General Manager of Agilent’s Microwave and Communications Division.

“By adding multi-measurement capability to our 89600 VSA software, which supports a wide variety of Agilent instruments, we will be providing the industry’s most flexible multi-measurement solution—a solution that enables engineers to see through the complexity in their wireless designs.”

The new software also runs in PC-based instruments or on Microsoft Windows-based PCs.

Basic properties of waves in an oscilloscope

A powerful tool used for designing and testing electronic devices, the oscilloscope helps engineers determine which components of a system are malfunctioning and which are behaving correctly. It also helps engineers determine whether a newly designed component is functioning in a manner that it has been intended.

The oscilloscope’s main purpose is to display electronic signals. The signals displayed on the screen of the oscilloscope allow users to determine the electronic system’s behavior. In order that users can fully understand the oscilloscope, it is vital that they also know basic signal theory.

Electronic signals are pulses or waves. The wave’s basic properties include amplitude, phase shift, period and frequency.

In engineering applications, amplitude has two main definitions. The first is defined as the magnitude of a disturbance’s maximum displacement, and is also known as the peak amplitude. The second is referred as the root-mean-square (RMS) amplitude. To calculate the waveform’s RMS voltage, users should first square the waveform, then identify its average waveform and take the square root.

The RMS amplitude of a sine wave is equivalent to 0.707 times the peak amplitude.

Another basic property of the wave is phase shift, which is the amount of horizontal translation among two identical waves. It can be measured in radians or degrees. In a sine wave, a cycle is represented by 360 degrees. Thus, if two sine waves differ by half a cycle, then 180 degrees is their relative phase.

In addition, the wave’s period refers to the amount of time needed for a wave to repeat itself, and is measured in terms of units of seconds.

Each periodic wave has a frequency, which is the number of times a wave repeats itself per second. It is also the reciprocal of the period.

Meanwhile, waveform is the representation or shape of a wave. A waveform offers users a lot of information regarding the signal, such as the sudden changes in voltage – whether it varies linearly or remains constant.

There are various standard waveforms, including sine waves, square/rectangular waves, triangular/sawtooth waves, pulses and complex waves.

Usually associated with alternating current (AC) sources, sine waves do not have constant peak amplitude.

A square waveform jumps periodically between two values, such that the lengths of the low segments are equal to the lengths of the high segments, while the lengths of low and high segments are not equal in a rectangular waveform.

In a triangular wave, the edges are referred to as ramps and their voltage linearly changes with time. A sawtooth wave appears similar in that either the back or front edge features a linear voltage response with time, although its opposite edge comes with an almost immediate drop.

A pulse refers to a sudden single disturbance in a constant voltage, while a complex wave refers to a combination of waveforms.

LeCroy WaveJet 312A Oscilloscope

LeCroy (www.lecroy.com) has introduced a two channel oscilloscope that offers 100 MHz bandwidth, a maximum real-time sampling rate of one GS/s and 500 kpts memory.

Featuring a footprint of only four inches with a large, bright 7.5-inch display, this compact and lightweight oscilloscope is easy to carry and ideal for use in work environments where space is a premium.

For additional analysis, the WaveJet 312A oscilloscope offers math capabilities that include difference, sum, product as well as FFT. These allow users to easily make measurements on the calculated waveforms using the cursors or the parameters.

The oscilloscope’s 26 automatic measurement parameters enable users to save time making measurements on the signals. Its min/max statistics function allows users to have a more in-depth look on the signals being measured.

The WaveJet 312A also features a replay mode, which enables users to go back in time and isolate anomalies, measure them with cursors or parameters and easily determine the source of the problem.

Its peak detect as well as equivalent time acquisition modes provide the flexibility needed in capturing and measuring signals. With peak detect, the oscilloscope can easily capture glitches as small as 1 ns, while its equivalent time sampling feature allows it to achieve a maximum sampling rate of 100 GS/s.

Knowing that saving screen images and waveforms is an important aspect of documenting results, LeCroy has specifically developed the Wavejet 312A to offer a front panel and a rear panel USB port for saving data to memory stick and printing hardcopies, respectively.

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.

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