Q. Please provide a block diagram sketch showing the trigger sources.

a. Distinguish between analog trigger processing and further digital processing such as delaying and counting.

b. Include triggering on aspects of acquired data.

c. Indicate which advanced trigger functions are software derived and those that are generated in hardware or either such as bus triggering.

Triggering Diagram

A. In the above diagram, the oscilloscope input channels (INPn) and external input (EXT IN) are analog signals that are converted to digital signals in threshold comparators.  All subsequent trigger processing is accomplished within digital circuitry.  The digital circuitry has programmable triggering parameters such as the upper (HLIM) and lower (LLIM) time limits for pulse with triggering.  These parameters can be adjusted in software for more complex triggering modes.  For example, in video triggering, software sets up pulse width triggering to trigger on the vertical sync pulse for the specified standard (PAL, NTSC, etc.) and adjusts the trigger delay to position the horizontal capture settings for the requested video line.

Q. Please discuss the pros and cons of analog vs. digital triggering in oscilloscopes. Which approach does your chosen scope use, and what are its specific advantages?

A. ZTEC oscilloscopes use analog threshold comparators and digital post-processing logic for all trigger processing.  Analog threshold comparators have some advantages such as (1) ability to capture transient pulses that are less than one sample interval, (2) ability to add analog trigger time interpolation for time accuracy of less than one sample interval, and (2) ability to trigger at levels exceeding the vertical data window.  Digital threshold comparators provide the advantages of (1) perfect noise-free vertical and horizontal accuracy and precision relative to the ADC data, (2) programmability and flexibility of digital hysteresis, and (3) fewer electronic components to save power, cost and complexity.

Q. Sometimes, subsystems within a scope may not be totally compatible with each other under all conditions. For example, a special acquisition or display mode may not support the full range of trigger capabilities. Please discuss the exceptions affecting triggering in your scope model.

A. ZTEC oscilloscopes have very few subsystem incompatibilities.  The various trigger modes are available for all configurations with the following exceptions:

(1)    the input signal conditioning must be identical to the trigger signal conditioning.  For example, if the input signal is AC coupled, the trigger on that input will also be AC coupled.

(2)    trigger time interpolation for equivalent-time sampling is only available on the analog input signals.  Equivalent-time sampling is incompatible with trigger sources from the EXT IN or the VXIbus/PXI backplane.

Q. Scopes with a high waveform update rate have become popular because they can help identify infrequent events or metastable states. Please describe how the architecture of your scope supports fast, triggered waveform update.

A. ZTEC oscilloscopes are architected for fast sequential capture of multiple waveforms.  Fast rearm (in as fast as a few hundred nanoseconds) is accomplished using segmented memory and fast acquisition mode.  In this acquisition mode, the oscilloscope’s deep memory is segmented into up to 32,768 smaller blocks of memory.  After each waveform acquisition, the oscilloscope increments to the next memory segment and rapidly rearms to wait for another trigger event.  Acquisition stops when the user disarms acquisition, or when a programmed number of waveforms have been acquired.

Segmented memory is also used for multi-waveform acquisition modes such as envelope or averaging.  For example, in an averaged waveform where 256 subsequent waveforms are averaged together, ZTEC oscilloscopes allow the user to selectively view the 256 individual component waveforms that make up the average waveform.

Q. What new or improved oscilloscope triggering features has your company introduced within the last 12 months? Please send press releases, datasheets, and photos.

A. A digital noise-reject trigger circuit was added to the trigger logic on ZTEC’s M-Class oscilloscopes with the release of the ZT462x in 2010.  The M-Class includes the ZT46xx, ZT42xx and ZT44xx series ranging from 500 MS/s to 4 GS/s with 8 to 14 bits of ADC resolution.

Listed below are some of our answers…. and be sure to check out our waveform generator product listing for more information!

Q. Please describe in detail at least one actual customer application that was addressed by your Arbs. How was the Arb controlled? What special features were critical to the application solution? Include waveforms if possible.

A. In the Military/Aerospace test market, ZTEC’s Arbitrary Waveform Generators (AWG) are often used as the baseband modulation sources for RF generators within radar and radio test applications.  For these customers, having multiple channels and comprehensive functionality is necessary to meet a variety of test requirements.  For example, Raytheon Missile Test Systems uses the 4-channel ZT5212VXI AWG in the RF test configuration of its common core tester.  The ZT5212VXI provides both common and independent clocking topologies.  When clocked commonly, some or all of the four AWG outputs are synchronized and phase coherent for applications such as I/Q modulation.  When independently clocked, the AWG outputs are completely autonomous for generating signals with different timing and sequencing.  In a third clock topology, one AWG channel is used as the modulation source for the carrier supplied by a second AWG channel.

Q. What new capabilities are provided in your company’s latest Arbs? Please describe new technical features that have been developed to support these capabilities. For example, some Arbs now maintain fine frequency resolution but avoid the small periodic jitter inherent in traditional DDS implementations.

A. Although ZTEC continues to develop AWGs using the latest chip sets to provide higher digital to analog converter (DAC) sample rates and bits of resolution, we have found that supporting legacy functionality is equally important to our Military/Aerospace test customers.  The high channel density and comprehensive AWG functionality of the ZT5210 series covers the majority of test requirements in the general-purpose DC to 50 MHz frequency range.  In addition to baseband, IF and video test applications, the 28Vpp voltage range of the ZT5210 series allows it to address applications such as power supply and transient testing.

Q. What technological trends are driving the Arb industry? For example, several manufacturers now offer Arbs with sufficiently high sample rates to directly generate modulated RF waveforms.

A. New high-speed DACs provide up to 16-bit resolution at sample rates in excess of 1 GS/s.  These devices provide the foundation for an AWG with the bandwidth and dynamic range to address modern radio and communication applications.  In combination with a quadrature modulator and advanced digital signal processing, high-speed DACs can be applied to create a full-featured vector signal generator with very high modulation bandwidth.  Example applications include commercial wireless standards such as Wi-Fi (IEEE 802.11), WiMAX (IEEE 802.16) and LTE, in addition to military standards such as those specified in the Joint Tactical Radio System (JTRS) initiative.  Also, broad modulation bandwidth allows multi-carrier signal generation, necessary for testing receiver adjacent channel rejection.  In summary, new technology will allow ZTEC to expand the applications for its AWG product line into RF test markets.

By Dr. Matthew Hunter, Chief Technical Officer

In addition to being the CTO at ZTEC, I am also a Research Professor in the Electrical Engineering Department at the University of Central Florida, specializing in DSP.  This means that I have the exciting opportunity to help graduate students learn about real-world signal processing.

Recently, I had the pleasure of helping one of the students prove out the applicability and performance of an adaptive algorithm using ZTEC’s new ZT8441 PXI RF/IF Digitizer .  The goal was to use the algorithm in an equalizer and measure the ability of the algorithm to correct for linear, frequency dependent distortion.

An equalizer is a type of adaptive system used in digital communications to correct for signal distortion in a wireless or wire line channel.  Distortion comes from many sources including band-limiting filters and multi-path fading, and without correction can cause bit errors in a communication system to increase.  A high level block diagram of the adaptive equalization process is shown in the figure below.  The system uses the desired signal and the output of the equalizer block to form an error signal. The error signal is used by the adaptive algorithm to adjust the equalizer such that the error is minimized.

In this experiment, we transmitted a QPSK modulated signal through a band limited channel (70 MHz band pass filter), received it with the ZT8441 and recovered the information symbols.  The channel frequency response over the transmitted signal band is given in the figure below.

A distortionless channel would have a flat magnitude and group delay.  As can be seen from the figure, the channel used in the experiment has significant variation over the signal band, so we expected significant distortion of the transmitted signal.  This was indeed the case as can be seen from the figure below.

Ideally, the symbols (shown as blue circles in the plot) would be points appearing at the coordinates (±0.707, ±0.707) only; clearly this is not the case.

Next, we tested the adaptive equalizer.  The corrected QPSK signal after equalization is shown in the figure below.  The equalizer output symbols are tightly grouped around the ideal coordinates, demonstrating the equalizer’s ability to correct for the distortion induced by the bandpass filter.

By Candy Martinez, Lead Software Engineer

After developing ZTEC’s latest Arbitrary Waveform Generator (AWG), the ZT5210, it seemed clear that the waveform library sequencing capabilities were extremely powerful.  To put this to the test, I wrote a fun, but challenging, demo to exercise this functionality.

I figured that since sound is just a sine wave at a specific frequency, the instrument’s output could drive a speaker.  Once I confirmed this, I decided to use the sequencing capabilities to play a song.  Though this initially didn’t seem too difficult, it quickly became apparent that converting music to the programmable AWG was not as trivial as it seemed at first glance.

The first difficulty is that the instrument is only able to play a sequence at a single clock frequency.  This meant that to achieve separate tones, I had to load sine waves of different lengths whose points would be played at a constant interval. See Figure 1.

ZWave

Figure 1: Waveforms of different frequencies

To make it simple, I did a simple 3-note song to start: Hot Cross Buns.  I loaded the three notes and created a quick sequence.  It became quite apparent that each note would have to be sustained for many cycles; though a little testing, I ended up with 1000 periods for the longer notes.  This is a consideration; the final waveform sequence generated was 1,500,000 points long. Fortunately the 5210 is capable of storing waveforms of over 32 million points.

Once the song was created, it also became clear that it was impossible to distinguish individual notes of the same tone.  To achieve this distinction, I had to add a DC wave to use as a breath, or pause, between notes.

In the end, the test worked perfectly.  Though the 5210 may not be designed for musicality, I was able to use the versatility of the sequencing to make it do what I wanted.  I’m more convinced than ever that the AWG can output anything that one can imagine.

The example code is attached here ztwaveM_music_example

Evaluating new test and measurement instrumentation is typically fun for us engineers as we get to see what the latest products have to offer and hopefully find a solution to our test problems. However, there are also invariably frustrations with the whole evaluation process.

First off, the evaluation may begin with a visit from your local sales rep. For some, this can be akin to getting a root canal as you sit through their 30 slide PowerPoint presentation when all you want to do is get your hands on the instrument and see for yourself what it can do. Next you have to arrange for a specific period of time that you can use the instrument based on the vendor’s loaner pool availability and your schedule. If you are at a larger company and receive a loaner instrument, you may need to log it in as a borrowed asset to avoid the time and frustration of explaining why you are shipping out the instrument when it is time to return it. Then there is actually finding the time to use the loaner instrument. You may have the best intentions of evaluating the instrument right after you receive it, but then something comes up and all of a sudden it’s two weeks later, you haven’t touched the instrument, and the sales rep is calling you and asking you to send it back.

Today, with many instruments having LAN/Ethernet ports, including LXI instruments (LAN eXtensions for Instrumentation), it is much easier to evaluate instruments remotely, at your convenience and in the comfort of your own office/lab/home. Plus, you don’t have to sit through the 30 slide presentation about why the product is so wonderful and you avoid the time and costs of arranging to receive and ship the instrument!

At ZTEC we make available our LXI oscilloscopes, digitizers, signal generators, arbitrary waveform generators and EPICS oscilloscopes to people who want to ‘test drive’ them remotely. Anyone interested in remotely evaluating our LXI instruments can contact us at http://www.ztecinstruments.com/contact/. Please note that these remote evaluations are available for anyone, anywhere. In fact, people in Europe and in Asia have remotely evaluated instruments set up here at our factory in Albuquerque.

For anyone who is interested, we provide information on how to connect to the units after downloading our free ZScope and ZWave applications which are available in Windows and Linux. Our evaluation setup consists of a digital oscilloscope and a function generator / arbitrary waveform generator so users can generate their desired signals, capture and analyze them using the oscilloscope; all while becoming familiar with our intuitive ZScope and ZWave applications.

People who want to remotely evaluate ZTEC’s EPICS oscilloscopes can request a demo at: http://www.ztecinstruments.com/contact/. ZTEC will then provide the user with the necessary EDM and MEDM panels and instructions on how to configure their Chanel Access (CA) settings to communicate with the instrument. Evaluators of the EPICS scope will have complete access to the instrument via EPICS/CA using the instrument’s 900+ process variables (PVs).

While remote LAN-based evaluation will suffice for many, for some people it won’t replace evaluating an actual instrument. Over the network, instrument responsiveness may be decreased and update rates can be slower than when directly connected to an instrument. Additionally, in case of an oscilloscope or digitizer, you don’t have the ability to directly connect your DUT or signal source to the instrument to see how it behaves. This latter problem can be solved by using the remotely-accessible ZTEC arbitrary waveform generator (AWG) to load a file representing your ‘real-world’ signal. Using the AWG to play back your signal and outputting it to the oscilloscope, you can display and analyze your signal on the oscilloscope. All of this is accomplished remotely, without ever being in physical contact with either the AWG or the oscilloscope.

The next time you are interested in evaluating a new piece of test and measurement equipment, find out if the vendor can arrange a remote evaluation for you. It may save you time, money and frustration.

One of the strengths of using modular instruments is the ability to write programs to perform an automated set of tasks. Generally this is done though a programming environment and a standard programming language like ANSI-C or COM. Though this may be the norm; there are also other ways to communicate and even quickly program using the standard SCPI string interface.

Using ZTEC’s ZFind command interface, it is easy to type in simple commands and queries:

Some more efficiency can be gained using “Tree-Walking” this lets you send multiple commands/queries on the same line:

Since the interface saves the command history, it is simple to change between a few commands using the up/down arrows on your keyboard. However, this starts to be less efficient with more than a few commands.

The command history can also be saved in its entirety. With the Save History option, you can save all of the commands that have been sent to a simple .txt file.

More advanced functionality is available through the command scripting. This allows the upload of a set of commands in a text file. This can either replay a previously saved command history, or can run though a manually generated list of commands.

Now the instrument can have complex programs run against it, using only a text file instead of compiling a program. The commands are standard SCPI, are provided in the instrument manual, are not case sensitive, and either the full or abbreviated command can be used.

In today’s electronic battlefield, the radar support system is crucial for success. In order to ensure that these systems are prepared for real-world encounters, the system must be thoroughly tested. Threat simulation and response measurements can be accomplished using a RF synthesizer and arbitrary waveform control source.

Background

The goal of threat simulation and response measurements is to replicate the target radar’s characteristics, and to test the target radar susceptibility to foreign signals. There are three main specifications that need to be taken into account when generating control signals:

1. Pulse Repetition Interval (PRI) – Time between output pulses
2. Pulse Width (PW)
3. Scan Rate – The amplitude modulation of the output which simulates the rotation and beam shape of the target radar antenna.

Scan Rate

The scan rate output modulation is independent from the output pulse. This requires a minimum of two output channels to properly stimulate the RF synthesizer. The ZT5210 waveform generator can be used to generate the two signals required from a single instrument. This channel density simplifies the development of software as well as hardware requirements and physical layout.

Scan rate is derived from the antenna beam shape and the rotation of the radar antenna. The simplest example of this is a standard AM modulated waveform (see Figure 2). As the beam shape and rotation of the antenna changes, the amount of time at the highest peak decreases, and the nulls become longer. This can be generated using an uploaded waveform based on actual antenna performance.

Simple Pulse Generation

In addition, the ZT5210 has a specific output mode that is extremely useful for radar simulation. Burst output mode makes puslse generation at a specific width and repetition interval easy to accomplish. This will minimize the development time required for simple radar pulse simulation.

Threat Emulation

Threat emulation is also needed to thoroughly test a radar system. A common threat is a walking target which simulates an object traveling to or from the target radar. This signal can be generated internally on the ZT5210 waveform generator using the built in Serial Data functionality. Serial Data allows the user to send a specific serial digital word (up to 64 bits) to the output. Sixty-four discrete locations for the target can be defined by adjusting any bit up or down. Serial Data can also be used to generate several targets by having 2 or more bits enabled at the same time. In addition, mathematical bit manipulations can simulate multiple targets traveling to and from the radar source.

Specialized Signals

Additionally, the user can upload an arbitrary waveform and generate any specialized signal that may be required. This upload functionality can also be combined with the waveform sequencer to create specific test patterns and scenarios that need to be tested. For example, a more natural threat path (smoother steps) can be generated. This can be extremely useful when the target radar is using advanced signal processing.

Most conventional digital storage oscilloscopes (DSO) offer 8 bit ADC resolution.  The 8-bit resolution may be sufficient for a visual waveform display, but will not be adequate for many applications that need to detect small changes in large signals.  With 8-bit resolution, the DSO cannot distinguish a signal level less than 0.39% of full-scale (see table). Consequently, an 8-bit DSO is unsuitable for many applications including transient signal capture, communication signal reception, frequency domain analysis, and semiconductor testing. As an alternative, high resolution DSOs offer more than 8 bit resolution to address these applications.

Comparison of specifications related to oscilloscope bit resolution:

Analog specifications such as noise, distortion and accuracy are more relevant for a high resolution DSO. Analog front end signal conditioning must have sufficiently low noise and distortion to not engulf the extra bits of ADC resolution.  Accuracy may also be important for some applications. A high resolution DSO with high accuracy can enable multimeter-like measurements at high speed.

The following lists example applications for high resolution digital oscilloscopes:

1. Transient signal capture: Transient events range from electronic signals to physical phenomena.  Often, transient signals have signal components and structures that must be resolved in the presence of large signals.  For example, a high resolution DSO can be used to simultaneously capture the turn-on transient and the steady-state ripple of a DC power supply.
   
2. Communication signal reception: Modern communication signals often encode digital data into small amplitude and phase changes within a sinusoidal carrier.  A high resolution DSO can be used to resolve the small changes between different symbols in the encoded signal transmission.
   
3. Frequency domain analysis: A Fast Fourier Transform (FFT) is a common mathematic algorithm used to transform a time domain DSO signal into the frequency domain for spectral analysis.  The quantization noise of an 8-bit DSO would limit the ability to resolve signals beyond its 50 dB dynamic range.  High resolution DSOs provide the additional dynamic range necessary for spectral analysis of sound, vibration, noise, audio, video, etc.
   
4. Semiconductor testing: When testing a semiconductor device such as a high-speed DAC, the DSO must have more resolution than the semiconductor device under test.  A high resolution DSO can be used to characterize the dynamic performance of high dynamic range semiconductor devices.

The Agilent / HP E1429B VXIbus oscilloscope is a differential oscilloscope that has been used for years in many ATE systems. Differential inputs are especially useful when input signals have undesirable common-mode components that must be rejected. The E1429B has been obsolete for years and a replacement is not available from Agilent. Fortunately, ZTEC has extensive experience with VXIbus oscilloscopes and the discontinued Agilent instruments in particular. The ZTEC ZT412-50 VXI is a modern VXI oscilloscope that provides extensive functionality, in most cases beyond that of the E1429B. Whereas the Agilent E1429B is a low-sample rate differential 12-bit oscilloscope, the ZT412-50 is a high sample rate pseudo-differential 16-bit oscilloscope. The E1429B has two separate input paths for each of its two ADCs: a single-ended path and a differential path. The ZT412-50 provides pseudo-differential inputs by using a math channel to difference a pair of its four single-ended inputs (using four ADCs and a DSP processor). The resulting differential waveforms for both oscilloscopes will be similar, but the internal architectures are different. Note that the ZT412-50 has an input offset zero self-calibration function that is particularly useful to zero out the common mode error for the pseudo-differential configuration. The table below provides a complete list of the differences between the E1429B and the ZT412-50. Note that the other specifications not listed below will be comparable for both instruments.

Because the instrument functionality, command set, and I/O ranges are different, there is some effort involved with the integration of the ZT412-50 in place of the E1429B. ZTEC’s application engineering team has significant experience with the functional differences between the E1429B and the ZT412-50, as well as the application details of using VXI oscilloscopes in ATE test programs. This experience is invaluable when assisting a test system integrator in successfully modifying an existing ATE system or TPS. Having successfully assisted customers with instrument replacement issues, the team at ZTEC appreciates the effort involved in additional test software development, validation and support required to replace an obsolete instrument.