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Efficiency is often the key factor in power converters, where efficiencies above 90% are required. This is true for battery operated IoT devices to get the most out of the battery, and it is also true for small DCDC converters supplied by a DC rail. Highly accurate power measurements are necessary to optimize the converter.
Designers need the capability of highly accurate power measurements to be able to improve converter efficiency during the design process. Improved efficiency results in a smaller battery, which means the converter size and overall system cost can be reduced. This allows developing a highly efficient converter design that can be released to production. To measure the efficiency of the converter, it is necessary to measure the input and output power with high accuracy.
A designer can follow an incremental process to increase the efficiency of the design. This incremental process consists of several small steps where the designer has to evaluate the improvement in efficiency after each design modification. The evaluation of the efficiency value is a challenging task because the improvement of the efficiency is the sum of several relatively small changes in the design. That is the reason why it is essential to have equipment with highest accuracy for power measurements. Rohde and Schwarz offers specialty power supplies that are perfect for challenging small power converter applications.
The R&S
NGM202 and R&SNGL202 provide great functionality and performance to measure, evaluate and optimize the important DCDC converter efficiency with just one instrument. The two-quadrant architecture allows them to function both, as a source and sink to provide highest flexibility. The highly precise read-back measurement capability for voltages and currents at the input and output offers the designer a very simple solution where only one device is required to measure the efficiency. The efficiency measurement setup of a DC-DC switching converter hence only consists of the power supply and the DUT connected to the two channels. Optional remote sensing connections increase the accuracy at higher currents.
Channel 1 is configured to work as a constant voltage source that supplies the converter with the required voltage and current (source). Channel 2 is configured to operate as a load in constant current mode (sink) to load the converter with a valid operational current based on the converter specification. A reasonable overcurrent protection level of the source as well as the prevention of the DUT’s overcurrent detection need to be considered in the configuration of the device. The voltage and current at the input and output are measured internally, and therefore the input and output power can be calculated and displayed on the screen.
The efficiency measurements at different load conditions shown in the table below indicate that the converter is already an efficiency-optimized converter. The R&SNGM202 or R&SNGL202 let you determine the efficiency of your individual circuitries and layouts. This means that in addition to going through the discussed optimization process to improve efficiency, the designer has to perform multiple measurements to validate the efficiency under all circumstances. This effort can be reduced tremendously by using the remote control functionality that allows to automatically create efficiency traces with an external script and a piece of software.
Oscilloscopes are everyday instruments for engineers and electricians. Maintenance tasks, however, sometimes require very specific measurements that are not available as standard functionality or are difficult to set up manually. For instance, the R&SRTH-K38 user scripting option solves one of such non-conventional requirements.
As are a railway engineer, a user is definitely dealing with the task of verifying the quality of electric communications signals, for example to determine the position of a train on its track. This is usually done by dividing the track into sections of rail with alternating frequencies, typically 95 Hz and 105 Hz. When a train is located within a specific section, the wheels short circuit the signal, indicating the position of the train to the receiver.
Such a specific measurement is certainly not a standard functionality on any handheld oscilloscope. Sometimes automatically executed setup on the device, a display of the maximum values of the currents and a graphical representation are requested in order to make operation as simple as possible for the engineers.
The R&SRTH-K38 user scripting software option makes the R&SScope Rider RTH handheld oscilloscope a powerful tool for automated or guided non-standard measurements in maintenance and service applications.
The option allows users to run individual measurement scripts on the device using the built-in web browser, JavaScript and the full functionality of the instrument via SCPI commands. It provides an easy-to-program and easy-to-use HTML user interface for fast measurement in the field. The user script is a combination of HTML to for the user interface and JavaScript to control the instrument via SCPI commands. Besides, a simple user interface can be designed with the help of this option.
To measure the railway isolation, an R&SRT-ZC03 current clamp is connected to the railway track and channel 1 of the R&SRTH. Then the R&SRTH-K38 user script option is activated. Overall, it is an extremely simple process and only requires three interactions.
The user script automatically configures the instruments into spectrum mode, sets the cursor to the defined frequencies and reads out the spectral amplitude at the respective frequencies. The currents for the four defined frequencies are converted into Ampere from the dBA values in spectrum mode as follows:
The current values are displayed in A, mA or μA in an HTML based browser window of the oscilloscope. The script not only automates the entire measurement procedure, it also makes it possible to perform sequenced cursor measurements at more than two frequencies.
In the JavaScript program, four additional variables are used to track the maximum current for each frequency and to display this information. In addition, a trend plot displays and logs the current values over time with automatic adjustment of the vertical scale of the graph. To reset the maximum value and restart the measurement, a counter and a “Reset Max Values” button were added. Finally, an Autorange function automatically sets the vertical scaling of the oscilloscope to match the current values and avoid overranging.
You can find an exemplary display screenshot below:
Detailed instructions on how to generate a user script for the R&SRTH-K38 option and how to load it onto the device can be found in the R&SScope Rider RTH user manual.
The correction of a bad circuit can be difficult with conventional edge triggers because the error state cannot be selected precisely. That is the reason why modern oscilloscopes offer various digital triggers that are specialized to address specific problems.
A digital trigger is a very unique and innovative concept. The benefit of this is that you are actually triggering on the same waveform that you are viewing on the screen. This means that the sensitivity of the trigger circuit precisely matches that of the scope, as well as the noise, the raise time and all the other characteristics of the trigger circuit precisely match the scope. Therefore, there is essentially zero trigger jitter. More importantly, one can always trigger on any signal that can be viewed.
The specialized digital triggers from Rohde & Schwarz are extremely accurate because they directly access the acquired samples and support a large selection of trigger conditions. These permit targeted debugging of recurring development tasks. In addition to the standard settings, additional qualifiers such as >, <, = and ≠ are available to expand the scope of application. Most triggers can be used on both analog and digital channels.
Below, a selection of specialized digital trigger types should be explained briefly. For a better understanding, some pictures were added in order to explain the specific functionality more clearly.
Width & glitch. The width trigger acts directly on the duration of a positive or negative pulse. Very short pulse widths are referred to as glitches. These triggers are used during the analysis of pulse width modulations, for example with rotary encoders. They are also important in the analysis of logic circuits where missing clock pulses can lead to very large pulse widths, or glitches can interfere with the circuit.
Timeout & interval. These two trigger modes expand the pulse width trigger functionality in two directions. The timeout trigger checks whether or not a pulse is followed by another pulse within a defined time window. The interval trigger checks the distance between two pulses of the same polarity. This makes it easy to find any missing clock pulses.
Pattern & state. The pattern trigger is used for measurements on parallel buses because it makes it possible to logically link pulse width triggers on multiple channels. The state trigger is different in that it references the pattern to a clock edge. Both triggers permit targeted isolation of complex circuit states, such as those that occur on parallel buses.
Data2Clock & setup-and-hold. The Data2Clock or setup-and-hold trigger checks two special timings on the data line as a function of the circuit clock pulse. A violation of these time relationships can easily perpetuate in logic circuits and must be avoided at all costs. This is critical for memory ports, for example.
Rise time. A faulty rise time for a signal can lead to timing problems during on/off switching operations of DC power supply units. These problems can easily be isolated using the rise time trigger. This trigger determines whether the level of a signal reaches a target threshold value within the defined time window.
Runt. A rise time that is too slow can lead to a runt, i.e. a pulse that is too low. The runt trigger can be used to define the lower and the upper pulse height limits as well as the pulse length limits. This makes it possible to specifically isolate metastable states in circuits.
Window. The window trigger checks whether the signal is inside or outside a defined voltage range. This check is performed with a time limit for timed segments. The window trigger is used to analyze voltage deviations in power supply units.
TV/video. The TV/video triggers represent a special class of triggers that resemble the protocol triggers. These triggers can be linked to specific components, such as the lines and frames of various video standards, including PAL, NTSC and HD 1080p.
Oscilloscopes are widely used for electrical designing as well as for testing and debugging almost anything that runs electricity. They are primarily used to measure and display voltage versus time for periodic or repeating waveforms. Modern oscilloscopes, however, can also easily display and hold non-periodic waveforms. Besides, they have several other functions such as the automatic measurement of parameters like peak-to-peak voltage or frequency, ability to look at serial buses and mixed-signal analysis and to do frequency domain analysis for signals – similar to a spectrum analyzer.
To explain the operating principle of an oscilloscope, typically four basic elements are used. In the following, these four elements will be explained in detail.
The vertical section controls the magnitude (amplitude) of the signal under test. A very common task when using an oscilloscope is scaling the displayed waveform using the “volts/div” control. This setting controls the amplification or attenuation of the input signal. If the “volts per division” control is being increased, the waveform shrinks and if it is being decreased, the waveform grows. The “offset” control is used to change the vertical position of the signal, i.e. to move the waveform up or down on the screen. The most important thing to keep in mind when configuring the vertical system of a digital oscilloscope is to use the volts per division control in such a way that the waveform is maximized and fills the complete display vertically. In other words, the positive and negative peaks should be as close to the top and bottom as possible, without clipping the waveform. This is necessary to use all available bits of the oscilloscope’s ADC (analog-to-digital converter) which results in an optimized quantization of the signal.
The horizontal section of an oscilloscope controls the time base of the measured signal, whereas the time corresponds to the horizontal axis of the signal display. The control is used to scale and position the waveform horizontally - similar to the vertical system. The “seconds per division” changes the horizontal scaling of the signal and the control “horizontal position” moves the signal to left or right. The sampling rate is one important parameter to analyze a signal using an oscilloscope. The oscilloscope digitizes the input signal at a given sample rate – usually noted as “samples per second”. These samples are stored in memory and together these make up a so-called waveform record. As the sample rate is being increased, the horizontal (time) resolution of the signal increases which helps to capture fast signal changes with more details. This also increases the probability of seeing or catching infrequent events. Higher sample rates however, create greater storage requirements.
This system is very important since triggering is needed for almost all oscilloscope measurements. Essentially, a trigger defines the conditions that have to be met before the oscilloscope begins an acquisition or begins taking samples. The trigger condition could be as simple as a defined threshold level that the signal amplitude crosses, or more complex like a specific frame in a communication signal. The correct trigger can stabilize a repeating or periodic signal, such as a sign wave, by causing each sweep to start at a given point on the signal. A trigger can also be used to capture non-periodic single events like a single pulse or a burst, etc. Depending on the signal to be measured, it is crucial to set the trigger properly. There are many different trigger types. They can be both, analog or digital. Modern scopes can trigger on things like pulse widths, runts, glitches, etc. A commonly used trigger, however, is the so-called edge triggering. In edge triggering, the user defines a voltage value and the trigger occurs when that threshold is crossed, either on the rising edge or on the falling edge on a waveform.
Once the signal is recorded as described before, it is shown on the display section of the oscilloscope. Modern digital oscilloscopes have touchscreens that allow straightforward access to helpful measurement functions and signal settings, such as zooming in and out of a signal and using cursors or markers to make manual measurements. Besides, there is also a large number of automated functions for analyzing or measuring the acquired waveforms like peak or peak-to-peak voltage, frequency, rise and fall times, slew rate, crest factor or pulse counts etc.
Oscilloscopes enable their users to perform an extremely broad variety of measurements, ranging from general purpose tests to compliance tests of specific industry standards. Rohde & Schwarz oscilloscopes have outstanding features like e.g. digital trigger, deep memory, frequency response analysis (Bode plot), real-time de-embedding, fast update rates, and unique low noise.
Explore the Rohde & Schwarz oscilloscope portfolio including the R&SScope Rider handheld oscilloscope, entry level oscilloscopes such as R&SRTC1000 or R&SRTB2000 as well as mid-class oscilloscopes such as R&SRTM3000 and find the right solution that matches your needs.
The new era of performance power supplies from Rohde & Schwarz has now begun with the launch of the R&SNGP800 series. These power supplies are designed for versatile applications. They are ideal when speed and advanced programming features are deciding factors in test performance.
The R&SNGP800 power supply series, comprising five powerful models with 400 or 800 W, provides maximum power at a variety of operating points. The new generation of power supplies provides two or four output channels which can each supply maximum output power up to 200 W, maximum voltage up to 64 V or maximum current up to 20 A. Electrically equivalent and galvanically isolated outputs can be wired in series or parallel for up to 250 V or 80 A. The large high-resolution touchscreen and the intuitive operating concept allow you to enter values much faster and to display statistics in realtime.
There are different classes of power supplies, while the R&SNGP800 power supplies belong to the performance class. These kinds of instruments are typically used in labs, ATE applications and production lines. Features such as DUT protection, fast programming and command processing times and downloadable V and I sequences are distinguishing and make these instruments great on the bench or in an automated test system.
NGP800 power supply series? NGP800 combines four power supplies in one single instrument. This allows saving costs and valuable space on the bench or in the rack. The large high-resolution touch display makes operation easy. Quick navigation is guaranteed and the home screen provides a clear overview of all channels. Each channel can be selected for a more detailed view, including real-time statistics for power, voltage and current measurements. Besides, the user gets the maximum power at various operating points. In case the application requires more voltage or current, parallel and serial operation is possible by connecting the outputs. NGP800 includes important protection functions, including an OCP, OVP as well as an OPP. These are essential to protect your DUT during limit testing. The electronic fuses can be set individually with programmable response behaviour and sensitivity; fuses can also be linked to other channels with the fuse link function. Using safety limits the power supply can be restricted to values that are not dangerous for the DUT.NGP800 power supplies come with pluggable 8-pin terminal blocks for the rear output connections. The optional digital I/O allows to setup advanced trigger systems that can also be used to synchronize multiple instruments. The output voltages and currents can be controlled directly and much faster with external control voltages from 0 V to 5 V via the optional analogue input interface.Precompliance, as well as debugging tests, are most commonly done with the help of a spectrum analyzer or an oscilloscope. The approach and diagnostic techniques of oscilloscopes were discussed in the last blog post.
This article’s focus is on spectrum analyzers. With built-in CISPR detectors, they offer advanced functions that can simplify EMI debugging. For debugging and locating emission sources using a spectrum analyzer, the R&SFPC1000 and R&SFPC1500 spectrum analyzers offer outstanding performance. Together with the R&SHZ-17 near-field probe set, this is an excellent solution used for locating the source and EMI debugging. The R&SHZ-16 preamplifier improves measurement sensitivity up to 3 GHz, with approx. 20 dB gain and a noise figure of 4.5 dB.
The R&SFPC1500 spectrum analyzer is an affordable, multipurpose instrument. Providing features of a spectrum analyzer, a signal generator and a network analyzer, it is perfect for EMI precompliance measurements. Besides, the instrument is suitable for general development, debugging and verification of electronic designs. A spectrum analyzer offers EMI-specific detectors (quasi-peak, CISPR-average), can easily measure very low amplitudes and high frequencies. Besides, the instruments offer longer gapless recording and wide dynamic ranges for detecting small signals in the vicinity of large signals. Another benefit is the availability of a dual-logarithmic axes display and a documentation PC software. However, a spectrum analyzer is not as versatile and more expensive compared to an oscilloscope.
By testing radiated emissions, you measure the electromagnetic field strength of unintentional emissions generated by your products. These emissions are inherent to any electrical circuit. The R&SFPL high-end as well as the R&SFPH handheld spectrum analyzers are a good choice for locating the source of unwanted emissions.
EMI measures comprise not only radiated emissions but also conducted emissions propagating towards the mains supply. In order to test conducted emissions, you can use the R&SFPC1000 and the R&SFPC1500 spectrum analyzers to analyze the level of RF energy coupled to the mains supply. This, however, requires the RF signal to be separated from the mains supply and stabilized to 50 Ω. This is achieved using a line impedance stabilization network.
Oscilloscopes are the workhorses for power electronics engineers. With powerful and easy-to-use FFT analysis capabilities, their application fields extend to EMI debugging – and that saves a lot of time and money. A typical task is verifying the effectiveness of an EMI filter – early in the development phase.
Rohde & Schwarz oscilloscopes offer a powerful, easy-to-use FFT analysis functionality to measure the magnitude of the frequency component. Users are able to see the time domain related signals at the same time and can therefore correlate unwanted spectral emissions with time domain events. This makes these oscilloscopes powerful standalone instruments for performing early conducted emission tests on power electronics designs. They can easily detect electromagnetic interference from electronic circuits with high speed and accuracy. The basic working principle of an oscilloscope is to capture signals when the input signal exceeds a specific trigger value, which helps to capture the peaks of the noise signal.
Overall, the major benefits of using an oscilloscope can be summarized as follows:
The FFT functionality of Rohde & Schwarz oscilloscopes is a powerful feature that enables designers to debug conducted emissions of power supplies. When using an oscilloscope to test conducted emissions, the R&SRTM3000 plus a line impedance stabilization network (LISN) are an ideal combination for debugging. To measure conducted emissions of a power supply, you need an LISN, for example the R&SHM6050-2, to decouple the device under test (DUT) from the external power supply.
Once the FFT is applied to the signal, and by selecting the center frequency and span, an oscilloscope can show the time domain and the frequency domain traces – comparable to what you can find on a spectrum analyzer. When comparing emission limits, you need to take into account that the signal might be attenuated due to the LISN. The EMI filter of the switched mode power supply is responsible for the reduced EMI spectrum; the noise generated at the input of the DC/DC converter is clearly visible in the left screenshot. With the low-pass-filter, you see that the conducted emissions on the input are effectively attenuated. For some frequencies, up to 30 dB attenuation is visible.
For debugging and locating emission sources using an oscilloscope, a combination of the R&SRTM3000 or the R&SRTA4000 oscilloscope and the R&SHZ-17 near-field probe set can do an excellent job. In addition to that, lab-class oscilloscopes have extended trigger and analysis capabilities that provide valuable tools for analyzing difficult EMI problems. Lab-class oscilloscopes’ ability to define multiple and different types of triggers for time, frequency and digital signals can be useful in examining the cause and effect of the captured signals.
To summarize, compared to medium-class oscilloscopes, lab-class oscilloscopes offer a few very useful features:
EMI debugging revolves around a simple idea – to have a convenient and affordable setup that can be used during product design for verification and early detection of potential problems. Each step of the product development process requires continuous EMI testing that can be performed by different types of test equipment. Most commonly debugging and pre-compliance tests are done with the help of a spectrum analyzer or an oscilloscope with near-field probes.
Oscilloscopes together with spectrum analyzers offer a wide range of diagnostic techniques that can be helpful during any stage of the product developmental cycle – ensuring that the product successfully passes full EMC compliance testing, making it ready for market on time, without investing in additional equipment.
If you are looking to perform EMI pre-compliance tests up to 3 GHz, Rohde & Schwarz offers a portfolio of instruments dedicated to cost-efficient EMI testing and debugging. The instruments tackle EMI problems from various perspectives. Each instrument category offers a different approach and diagnostic techniques that can complement each other at different stages of the product development cycle.
Oscilloscopes are typically already available at the R&D engineer’s bench. Therefore oscilloscopes are often considered as an economically sensible tool. Their ability to perform EMI debugging tasks provides a more cost-effective solution that eliminates the need for additional equipment. State-of-the-art oscilloscopes are ideal tools for EMI debugging because they are able to transform signals from the time domain into the frequency domain (by fast Fourier transform (FFT)). The combination of synchronized time domain and frequency domain analysis with advanced triggers allows quick insight into EMI problems. Besides, EMI debugging with an oscilloscope enables correlation of interfering signals with time domain events. Oscilloscopes can easily detect electromagnetic interference from electronic circuits with high speed and accuracy. The basic working principle of an oscilloscope is to capture signals when the input signal exceeds a specific trigger value, which helps to capture the peaks of the noise signal.
Spectrum analyzers are commonly used in pre-compliance test setups. With built-in CISPR detectors, they offer advanced functions that can simplify EMI debugging. Compared to the use of an oscilloscope, it is much more cost-intensive and a spectrum analyzer is not as versatile. However, there are also some important benefits using a spectrum analyzer. A spectrum analyzer can easily measure very low amplitudes and high frequencies. Spectrum analyzers offer longer gapless recording and provide wide dynamic ranges for detecting small signals in the vicinity of large signals. Besides, spectrum analyzers offer EMI-specific detectors (quasi-peak, CISPR-average). Apart from that, there is a dual-logarithmic axes display available.
Electromagnetic compatibility (EMC) testing is a critical part of any product development journey. EMC is strictly regulated by development and production standards to ensure products’ safe operation next to other electronic devices. The fact is that all electronic devices emit electromagnetic waves while they operate. However, for some devices, it is an undesired byproduct. The emissions can come from many sources and can be strong enough to interfere with other electronic devices. Electromagnetic interference (EMI) is always an unwanted occurrence, whereas EMC is mandatory for all electronic products. EMC is especially important in areas where precise tasks are carried out or where even slight disturbances might cause serious consequences. The overall aim is to eliminate or reduce EMI below certain limits.
EMI as an unwanted occurrence can be continuous, existing constantly in the background, or it can occur for a short period of time. When considering the way EMI is propagating from the source to the device affected by the noise, radiated and conducted emissions can be differentiated. Radiated emissions are emitted by a device, propagate over the air and can affect other devices. In comparison, conducted emissions propagate through electronic connections (e.g. cables) from one device to other directly connected devices.
As illustrated in the figure, pre-compliance and debugging tests should already be performed early in the development process in order to ensure that EMC standards are adhered to. Also, the possibility of having to redesign a product due to EMC testing failures shrinks. This contributes to meeting the development budget and time-to-market.
In most cases, the development process turns out as a sequence of standard steps. Near-field measurements are used to localize the source of interference. After the noise source has been located, the behavior of the interference can be analyzed and corrective measures assessed. A final pre-compliance measurement is performed before going into the compliance stage. Each step requires continuous testing that can be performed by different types of test equipment. While pre-compliance, as well as debugging tests, are mostly done with the help of a spectrum analyzer respectively an oscilloscope, compliance tests are usually done with EMI receivers.
