Expanded Low-Power, Open-Frame AC-DC Power Supply Series

CUI recently added four low-power, open-frame AC-DC power supply series to its VOF product family. The VOF‑6B, VOF‑10B, VOF‑15B, and VOF‑20B series are 6-, 10-, 15-, and 20-W power additions to CUI’s general-purpose AC-DC power supply portfolio that currently ranges from 6 to 300 W. Well suited for space-constrained, low-power ITE, industrial, and consumer applications, the new models are housed in compact, board-mount packages measuring as small as 1.913″ × 0.917″ × 0.638″ (48.6 × 23.3 × 16.2 mm). They feature industry-standard pinouts, 4-kVAC isolation, and no-load power consumption less than 100 mW.CUI low_power_open_frame

The 6-to-20-W modules feature a wide universal input voltage range of 85 to 264 VAC with single output voltages of 5, 9, 12, 15, 24, and 48 VDC, depending on the series. Operating temperatures at full load range from –25° to 50°C, derating to 50% load at 70°C. All of the models carry UL/cUL and TUV 60950-1 safety certifications and meet EN 55032 Class B and FCC Class B limits for radiated emissions. Protections for short circuit, over current, and over voltage come standard. The series also carry a minimum MTBF of 300,000 h at 115 VAC at 25°C ambient, calculated per MIL‑HDBK‑217F.

Prices for the VOF‑6B, VOF‑10B, VOF‑15B, and VOF‑20B series start at $7.57 per unit in 100-piece quantities.

Source: CUI, Inc.

Evaluating Oscilloscopes (Part 4)

In this final installment of my four-part mini-series about selecting an oscilloscope, I’ll look at triggering, waveform generators, and clock synchronization, and I’ll wrap up with a series summary.

My previous posts have included Part 1, which discusses probes and physical characteristics of stand-alone vs. PC-based oscilloscopes; Part 2, which examines core specifications such as bandwidth, sample rate, and ADC resolution; and Part 3, which focuses on software. My posts are more a “collection of notes” based on my own research rather than a completely thorough guide. But I hope they are useful and cover some points you might not have otherwise considered before choosing an oscilloscope.

This is a screenshot from Colin O'Flynn's YouTube video "Using PicoScope AWG for Testing Serial Data Limits."

This is a screenshot from Colin O’Flynn’s YouTube video “Using PicoScope AWG for Testing Serial Data Limits.”

Topic 1: Triggering Methods
Triggering your oscilloscope properly can make a huge difference in being able to capture useful waveforms. The most basic triggering method is just a “rising” or “falling” edge, which almost everyone is (or should be) familiar with.

Whether you need a more advanced trigger method will depend greatly on your usage scenario and a bit on other details of your oscilloscope. If you have a very long buffer length or ability to rapid-fire record a number of waveforms, you might be able to live with a simple trigger since you can easily throw away data that isn’t what you are looking for. If your oscilloscope has a more limited buffer length, you’ll need to trigger on the exact moment of interest.

Before I detail some of the other methods, I want to mention that you can sometimes use external instruments for triggering. For example, you might have a logic analyzer with an extremely advanced triggering mechanism.  If that logic analyzer has a “trigger out,” you can trigger the oscilloscope from your logic analyzer.

On to the trigger methods! There are a number of them related to finding “odd” pulses: for example, finding glitches shorter or wider than some length or finding a pulse that is lower than the regular height (called a “runt pulse”). By knowing your scope triggers and having a bit of creativity, you can perform some more advanced troubleshooting. For example, when troubleshooting an embedded microcontroller, you can have it toggle an I/O pin when a task runs. Using a trigger to detect a “pulse dropout,” you can trigger your oscilloscope when the system crashes—thus trying to see if the problem is a power supply glitch, for example.

If you are dealing with digital systems, be on the lookout for triggers that can function on serial protocols. For example, the Rigol Technologies stand-alone units have this ability, although you’ll also need an add-on to decode the protocols! In fact, most of the serious stand-alone oscilloscopes seem to have this ability (e.g., those from Agilent, Tektronix, and Teledyne LeCroy); you may just need to pay extra to enable it.

Topic 2: External Trigger Input
Most oscilloscopes also have an “external trigger input.”  This external input doesn’t display on the screen but can be used for triggering. Specifically, this means your trigger channel doesn’t count against your “ADC channels.” So if you need the full sample rate on one channel but want to trigger on another, you can use the “ext in” as the trigger.
Oscilloscopes that include this feature on the front panel make it slightly easier to use; otherwise, you’re reaching around behind the instrument to find the trigger input.

Topic 3: Arbitrary Waveform Generator
This isn’t strictly an oscilloscope-related function, but since enough oscilloscopes include some sort of function generator it’s worth mentioning. This may be a standard “signal generator,” which can generate waveforms such as sine, square, triangle, etc. A more advanced feature, called an arbitrary waveform generator (AWG), enables you to generate any waveform you want.

I previously had a (now very old) TiePie engineering HS801 that included an AWG function. The control software made it easy to generate sine, square, triangle, and a few other waveforms. But the only method of generating an arbitrary waveform was to load a file you created in another application, which meant I almost never used the “arbitrary” portion of the AWG. The lesson here is that if you are going to invest in an AWG, make sure the software is reasonable to use.

The AWG may have a few different specifications; look for the maximum analog bandwidth along with the sample rate. Be careful of outlandish claims: a 200 MS/s digital to analog converter (DAC) could hypothetically have a 100-MHz analog bandwidth, but the signal would be almost useless. You could only generate some sort of sine wave at that frequency, which would probably be full of harmonics. Even if you generated a lower-frequency sine wave (e.g., 10 MHz), it would likely contain a fair amount of harmonics since the DAC’s output filter has a roll-off at such a high frequency.

Better systems will have a low-pass analog filter to reduce harmonics, with the DAC’s sample rate being several times higher than the output filter roll-off. The Pico Technology PicoScope 6403D oscilloscope I’m using can generate a 20-MHz signal but has a 200 MS/s sample rate on the DAC. Similarly, the TiePie engineering HS5-530 has a 30-MHz signal bandwidth, and similarly uses a 240 MS/s sample rate. A sample rate of around five to 10 times the analog bandwidth seems about standard.

Having the AWG integrated into the oscilloscope opens up a few useful features. When implementing a serial protocol decoder, you may want to know what happens if the baud rate is slightly off from the expected rate. You can quickly perform this test by recording a serial data packet on the oscilloscope, copying it to the AWG, and adjusting the AWG sample rate to slightly raise or lower the baud rate. I illustrate this in the following video.

Topic 4: Clock Synchronization

One final issue of interest: In certain applications, you may need to synchronize the sample rate to an external device. Oscilloscopes will often have two features for doing this. One will output a clock from the oscilloscope, the other will allow you to feed an external clock into the oscilloscope.

The obvious application is synchronizing a capture between multiple oscilloscopes. You can, however, use this for any application where you wish to use a synchronous capture methodology. For example, if you wish to use the oscilloscope as part of a software-defined radio (SDR), you may want to ensure the sampling happens synchronous to a recovered clock.

The input frequency of this clock is typically 10 MHz, although some devices enable you to select between several allowed frequencies. If the source of this clock is anything besides another instrument, you may have to do some clock conditioning to convert it into one of the valid clock source ranges.

Summary and Closing Comments
That’s it! Over the past four weeks I’ve tried to raise a number of issues to consider when selecting an oscilloscope. As previously mentioned, the examples were often PicoScope-heavy simply because it is the oscilloscope I own. But all the topics have been relevant to any other oscilloscope you may have.

You can check out my YouTube playlist dealing with oscilloscope selection and review.  Some topics might suggest further questions to ask.

I’ve probably overlooked a few issues, but I can’t cover every possible oscilloscope and option. When selecting a device, my final piece of advice is to download the user manual and study it carefully, especially for features you find most important. Although the datasheet may gloss over some details, the user manual will typically address the limitations you’ll run into, such as FFT length or the memory depths you can configure.

Author’s note: Every reasonable effort has been made to ensure example specifications are accurate. There may, however, be errors or omissions in this article. Please confirm all referenced specifications with the device vendor.

Evaluating Oscilloscopes (Part 3)

In Part 3 of my series on selecting an oscilloscope, I look at the software running the oscilloscope and details such as remote control, fast Fourier transform (FFT) features, digital decoding, and buffer types.

Two weeks ago, I covered the differences between PC-based and stand-alone oscilloscopes and discussed the physical probe characteristics. Last week I discussed the “core” specifications: analog bandwidth, sample rate, and analog-to-digital converter (ADC) resolution. Next week, I will look into a few remaining features such as external trigger and clock synchronization, and I will summarize all the material I’ve covered.

Topic 1: Memory Depth
The digital oscilloscope works by sampling an ADC and then stores these samples somewhere. Thus an important consideration will be how many samples it can actually store. This especially becomes apparent at higher sample rates—at 5 gigasamples per second (GS/s), for example, even 1 million samples (i.e., 1 megasample or 1 MS) means 200 µs of data. If you are looking at very low-cost oscilloscopes, be aware that many of them have very small buffers. Searching on eBay, you can find an oscilloscope such as the Hantek DSO5202P, which has a 1 GS/s sample rate and costs only $400. The record length is only 24 kilosamples (KS) however, which would be 24 µs of data. You can find even smaller buffers:  the Tektronix TDS2000C series has only a 2,500-sample (2.5 KS) buffer length. If you only want to look around the trigger signal, you can live with a small buffer. Unfortunately, when it comes to troubleshooting you rarely have a perfect trigger, and you may need to do a fair amount of “exploration.”  A small buffer means the somewhat frustrating experience of trying to capture the signal of interest within your tiny window of opportunity.

Even if the buffer space is advertised as being huge, you may not be able to easily access the entire space. The Pico Technology PicoScope PS6403D advertises a 1-GS buffer space, one of the largest available. With the PC-based software you can configure a number of parameters; however, it always seems to limit the sample buffer to about 500 MS.  I do admit it’s fairly impressive that this still works at the 5 GS/s sample rate, since that suggests a memory bandwidth of 40 Gb/s! Using the segmented buffer (discussed later in this article) enables use of the full sample memory, but it cannot record a full continuous 1 GS trace, which you might expect based on the sales pitch.

Topic 2: FFT Length
Oscilloscope advertisements often allude to their ability to perform in a “spectrum analyzer” mode. In reality, what the oscilloscope is doing is performing an FFT of the measured signal. One critical difference is that a spectrum analyzer typically has a “center frequency” and you are able to measure a certain bandwidth amount to either side of that center frequency. By sweeping the center frequency, you can get a graph of the power present in the frequency system over a very wide range.

Using the oscilloscope’s FFT mode, there is no such thing as the center frequency. Instead you are always measuring from 0 Hz up to some limit, which is usually user-adjustable. The limit is, at most, half the oscilloscope’s sample rate but may be further limited by the oscilloscope’s analog bandwidth. Now here is the trick—the oscilloscope will specify a certain “FFT length,” which is how many points are used in calculating the FFT. This will also define the number of “bins” (i.e., horizontal frequency resolution) in the output graph. Certain benchtop oscilloscopes may have very limited FFT lengths, such as those containing only 2,048 points.  This may seem fine for viewing the entire spectrum from 0–100 MHz. But what if you want to zoom in on the 95–98 MHz range? Since the oscilloscope is actually calculating the FFT from 0 Hz, it will have only ~60 points it can display in that range. It suddenly becomes apparent why you want very long FFT lengths—it allows you to zoom in and still obtain accurate results. You can set the oscilloscope sample rate down to zoom in on frequencies around 0 Hz. So, for example, if you want to accurately do some measurements at 1–10 kHz, it’s not a big issue since you can set a low enough sample rate so that the 2,048 points are distributed between 0–20 kHz or similar. And when you zoom in you’ve got lots of detail.

In addition to the improved horizontal detail, longer FFT lengths push down the noise floor.  If you do wish to use the oscilloscope for frequency analysis, having a long FFT length can be a huge asset. This is shown in Figure 1, which compares an FFT taken using a magnetic field probe of a microcontroller board. Here I’ve zoomed in on a portion of the spectrum, with the left FFT having 2,048 points, the right FFT having 131,072 points.

Figure 1: When zooming in on a portion of the fast Fourier transform (FFT), having a larger number of points for the original calculation becomes a huge asset. Also, notice the lower noise floor for the figure on the right, calculated with 131,072 points, compared to the 2,048 used for the figure on the left.

Figure 1: When zooming in on a portion of the fast Fourier transform (FFT), having a larger number of points for the original calculation becomes a huge asset. Also, notice the lower noise floor for the figure on the right, calculated with 131,072 points, compared to the 2,048 used for the figure on the left.

A note on selecting a unit: The very low-cost oscilloscopes with small data buffers will obviously use a very small FFT length. But specifications for some of the larger memory depth oscilloscopes, such as the Rigol Technologies DS2000, DS4000, and DS6000 models, show they use smaller FFT lengths.  These models use only 2,048 points, according to a document posted on Rigol’s website, despite their large memory (131 MS).  PC-based oscilloscopes seem to be the best, as they can perform the FFT on a powerful desktop PC, rather than requiring it be done in an embedded digital signal processor (DSP) or field-programmable gate array (FPGA). For example, the PicoScope 6403D allows the FFT length to be up to 1,048,576 points.

Topic 3: Segmented Buffer
A feature I consider almost a “must-have” is a segmented buffer. This means you can configure the oscilloscope to trigger on a certain event, and it will record a number of waveforms of a certain length. For glitches that occur only occasionally (which is, 90% of the time, why you are troubleshooting in the first place), this can speed up your ability to find details of what the system is doing during a glitch.

Figure 2 shows an example of the segmented buffer viewer on the PicoScope software, where the number of buffers can be configured up to 10,000. Similar features exist in the Rigol DS4000 and DS6000, which call each segment a “frame” and can record up to 200,000 frames! Once you have a number of segments/frames, you can either manually flip through looking for the glitch, or use features such as mask limit testing to highlight segments/frames that differ from the “usual.”

Figure 2

Figure 2: Segmented buffers allow you to capture a number of traces and then flip through them looking for some specific feature. Using mask-based testing will also speed this up, since you can quickly find “odd man out”-type waveforms.

Certain oscilloscopes might make the segmented buffer an add-on. For example, only certain Agilent Technologies 3000 X-Series models contain segmented buffers by default; others in that same family require you to purchase this feature for an extra $800! Of course, always review any promotional offers—Agilent has recently advertised that it will enable all features on that oscilloscope model for the price of a single option.

Topic 4: Remote Control/Streaming
One more advanced feature is controlling the oscilloscope from your computer. If you wish to use the oscilloscope in applications beyond electronics troubleshooting, you should seriously consider the features different oscilloscopes provide.

PC-based oscilloscopes tend to have a considerable advantage here, as they are typically designed to interface to the computer. It seems most PC-based oscilloscopes from popular suppliers come with nice application programming interfaces (APIs) for most languages: I’ve found examples in C, C#, C++, MATLAB, Python, LabVIEW, and Delphi for most PC-based oscilloscopes. Some of the “no-name” PC-based oscilloscopes you find on eBay do not have an API, so always check closely for your specific device.

Most of the stand-alone oscilloscopes also have a method of sending commands, typically using a standard such as the Virtual Instrument Software Architecture (VISA). However, I’ve found these stand-alone oscilloscopes seem to have a considerably slower interface compared to a PC-based oscilloscope. Presumably for the PC-based oscilloscope, this interface is critical to overall performance, whereas for the stand-alone it’s simply an “add-on” feature. This isn’t a sure thing, of course—for example, see the PC interface for the Teledyne LeCroy oscilloscope, as described in a company blog post. It looks to give you access to features similar to those of PC-based oscilloscopes (multiple windows, etc.).

Beyond just controlling the oscilloscope, another interesting feature is streaming mode. In streaming mode data is not downloaded to an internal buffer on the oscilloscope. Instead it streams directly over the PC interface (typically USB or Ethernet). This feature is considerably more complex to work with than simple PC-based control, as achieving fast streams via USB is not trivial. However, using streaming mode opens up many interesting features. For example, you could use your oscilloscope as part of a software defined radio (SDR). If you wish to use such a feature, be sure to carefully read the specification sheets for the streaming mode limitations.

Topic 5: Decoding Serial Protocols
Decoding of serial protocols is another useful feature. If you have a digital logic analyzer, it will almost certainly include the ability to decode serial protocols. But it can be helpful to have this feature in the oscilloscope as well. If you are chasing down an occasional parity error, you can use the oscilloscope’s analog display to see if the issue is simply a weak or noisy signal.

While most oscilloscopes seem to support this feature, many require you to pay for it. Typically PC-based oscilloscopes will include it for free, but stand-alone oscilloscopes require you to purchase it. For example, this feature costs $500 for the Rigol Technologies DS4000 series, $800 for the Agilent Technologies 3000X, and $1,100 for the Tektronix DPO/MSO3000 series. Depending on the vendor, it may include multiple protocols or only one. But if you wish to enable all available protocols, it could cost more than your oscilloscope! It would typically be cheaper to purchase a PC-based logic analyzer than it would be to buy the software module for your oscilloscope.

This is one of the major reasons I prefer PC-based oscilloscopes: There tends to be no additional cost for extra features! Without the decoding you can look at the signal and see if it “looks” noisy, but having the decoding built-in means you can easily point to the specific moment when the error occurs. I’ve got some examples of such serial decoding in my video below.

Topic 6: Software Features
I’ve already mentioned it a few times in passing, but you should always check to see what software features are actually included. You may be surprised to find out some features require payment—even some models adding the FFT or other “advanced math” features require payment of a substantial fee.

There is hope on the horizon for getting access to all features in stand-alone oscilloscopes at a reasonable cost. As I mentioned earlier, Agilent Technologies recently announced it would be providing access to all software features for the cost of one module in the X-2000, X-3000, and X-4000 series. Once this goes into effect, it means that it’s really just $500–$1,500 for decoding of all serial protocols and all math features, depending on your oscilloscope. They sell this as saving you up to $16,500. (Which to me just shows how insanely expensive all these software add-ons really are!) With luck, other vendors will follow suit, and perhaps even finally include these software options in the selling price.

If you’re looking at PC-based oscilloscopes, you’ll often be allowed to download the software and play with it, even if you don’t have an instrument. This can give you an idea of how “polished” the user interface is. Considering how long you’ll spend inside this user interface, it’s good to know about it!

Closing Comments
This week I covered a number of features revolving around the software running the oscilloscope. Next week I’ll be looking into a few remaining features such as external trigger and clock synchronization, which will round out this guide.

Author’s note: Every reasonable effort has been made to ensure example specifications are accurate. There may, however, be errors or omissions in this article. Please confirm all referenced specifications with the device vendor.

Evaluating Oscilloscopes (Part 2)

This is Part 2 of my mini-series on selecting an oscilloscope. Rather than a completely thorough guide, it’s more a “collection of notes” based on my own research. But I hope you find it useful, and it might cover a few areas you hadn’t considered.

Last week I mentioned the differences between PC-based and stand-alone oscilloscopes and discussed the physical probe’s characteristics. This week I’ll be discussing the “core” specifications: analog bandwidth, sample rate, and analog-to-digital converter (ADC) resolution.

Topic 1: Analog Bandwidth
Many useful articles online discuss the analog oscilloscope bandwidth, so I won’t dedicate too much time to it. Briefly, the analog bandwidth is typically measured as the “half-power” or -3 dB point, as shown in Figure 1. Half the power means 1/√2 of the voltage. Assume you put a 10-MHz, 1-V sine wave into your 100-MHz bandwidth oscilloscope. You expect to see a 1-V sine wave on the oscilloscope. As you increase the frequency of the sine wave, you would instead expect to see around 0.707 V when you pass a 100-MHz sine wave. If you want to see this in action, watch my video in which I sweep the input frequency to an oscilloscope through the -3 dB point.

Figure 1: The bandwidth refers to the "half-power" or -3 dB  point. If we drove a sine wave of constant amplitude and increasing frequency into the probe, the -3 dB point would be when the amplitude measured in the scope was 0.707 times the initial amplitude.

Figure 1: The bandwidth refers to the “half-power” or -3 dB point. If we drive a sine wave of constant amplitude and increasing frequency into the probe, the -3 dB point would be when the amplitude measured in the scope is 0.707 times the initial amplitude.

Unfortunately, you are likely to be measuring square waves (e.g., in digital systems) and not sine waves. Square waves contain high-frequency components well beyond the fundamental frequency of the wave. For this reason the “rule of thumb”  is to select an oscilloscope with five times the analog bandwidth of the highest–frequency digital signal you would be measuring. Thus, a 66-MHz clock would require a 330-MHz bandwidth oscilloscope.

If you are interested in more details about bandwidth selection, I encourage you to see one of the many excellent guides. Adafruit has a blog post “Why Oscilloscope Bandwidth Matters” that offers more information, along with links to guides from Agilent Technologies and Tektronix.

If you want to play around yourself, I’ve got a Python script that applies analog filtering to a square wave and plots the results, available here. Figure 2 shows an example of a 50-MHz square wave with 50-MHz, 100-MHz, 250-MHz, and 500-MHz analog bandwidth.

Figure 2: This shows sampling a 50-MHz square wave with 50, 100, 250, and 500-MHz of analog bandwidth.

Figure 2: This shows sampling a 50-MHz square wave with 50, 100, 250, and 500 MHz of analog bandwidth.

Topic 2: Sample Rate
Beyond the analog bandwidth, oscilloscopes also prominently advertise the sample rate. Typically, this is in MS/s (megasamples per second) or GS/s (gigasamples per second). The advertised rate is nearly always the maximum if using a single channel. If you are using both channels on a two-channel oscilloscope that advertises 1 GS/s, typically the maximum rate is actually 500 MS/s for both channels.

So what rate do you need? If you are familiar with the Nyquist criterion, you might simply think you should have a sample rate two times the analog bandwidth. Unfortunately, we tend to work in the time domain (e.g., looking at the oscilloscope screen) and not the frequency domain. So you can’t simply apply that idea. Instead, it’s useful to have a considerably higher sample rate compared to analog bandwidth, say, a five times higher sample rate. To illustrate why, see Figure 3. It shows a 25.3-MHz square wave, which I’ve sampled with an oscilloscope with 50-MHz analog bandwidth. As you would expect, the signal rounds off considerably. However, if I only sample it at 100 MS/s, at first sight the signal is almost unrecognizable! Compare that with the 500 MS/s sample rate, which more clearly looks like a square wave (but rounded off due to analog bandwidth limitation).

Again, these figures both come from my Python script, so they are based purely on “theoretical” limits of sample rate. You can play around with sample rate and bandwidth to get an idea of how a signal might look.

Figure 3

Figure 3: This shows sampling a 25.3-MHz square wave at 100 MS/s results in a signal that looks considerably different than you might expect! Sampling at 500 MS/s results in a much more “proper” looking wave.

Topic 3: Equivalent Time Sampling
Certain oscilloscopes have an equivalent time sampling (ETS) mode, which advertises an insanely fast sample rate. For example, the PicoScope 6000 series, which has a 5 GS/s sample rate, can use ETS mode and achieve 200 GS/s on a single channel, or 50 GS/s on all channels.

The caveat is that this high sample rate is achieved by doing careful phase shifts of the A/D sampling clock to sample “in between” the regular intervals. This requires your input waveform be periodic and very stable, since the waveform will actually be “built up” over a longer time interval.

So what does this mean to you? Luckily, many actual waveforms are periodic, and you might find ETS mode very useful. For example, if you want to measure the phase shift in two clocks through a field-programmable gate array (FPGA), you can do this with ETS. At 50 GS/s, you would have 20 ps resolution on the measurement! In fact, that resolution is so high you could measure the phase difference due to a few centimeters difference in PCB trace.

To demonstrate this, I can show you a few videos. To start with, the simple video below shows moving the probes around while looking at the phase difference.

A more practical demonstration, available in the following video, measures the phase shift of two paths routed through an FPGA.

Finally, if you just want to see a sine wave using ETS you can check out the bandwdith demonstration  I referred to earlier in the this article. The video (see below) includes a portion using ETS mode.


Topic 4: ADC Resolution
A less prominently advertised feature of certain oscilloscopes is the ADC bit resolution in the front end. Briefly, the ADC resolution tells you how the analog waveform will get mapped to the digital domain. If you have an 8-bit ADC, this means you have 28 = 256 possible numbers the digital waveform can represent. Say you have a ±5 V range on the oscilloscope—a total span of 10 V. This means the ADC can resolve 10 V / 256 = 39.06 mV difference on the input voltage.

This should tell you one fact about digital oscilloscopes: You should always use the smallest possible range to get the finest granularity. That same 8-bit ADC on a ±1 V range would resolve 7.813 mV. However, what often happens is your signal contains multiple components—say, spiking to 7 V during a load switch, and then settling to 0.5 V. This precludes you from using the smaller range on the input, since you want to capture the amplitude of that 7-V spike.

If, however, you had a 12-bit ADC, that 10 V span (+5 V to -5 V) would be split into 212 = 4,096 numbers, meaning the resolution is now 2.551 mV.  If you had a 16-bit ADC, that 10-V range would give you 216 = 65,536 numbers, meaning you could resolve down to 0.1526 mV. Most of the time, you have to choose between a faster ADC with lower (typically 8-bit) resolution or a slower ADC with higher resolution. The only exception to this I’m aware of is the Pico Technology FlexRes 5000 series devices, which allow you to dynamically switch between 8/12/14/15/16 bits with varying changes to the number of channels and sample rate.

While the typical ADC resolution seems to be 8 bits for most scopes, there are higher-resolution models too. As mentioned, these devices are permanently in high-resolution mode, so you have to decide at purchasing time if you want a very high sample rate, or a very high resolution. For example, Cleverscope has always advertised higher resolutions, and their devices are available in 10, 12, or 14 bits. Cleverscope seems to sell the “digitizer” board separately, giving you some flexibility in upgrading to a higher-resolution ADC. TiePie engineering has devices available from 8–14 bits with various sample rate options. Besides the FlexRes device I mentioned, Pico Technology offers some fixed resolution devices in higher 14-bit resolution. Some of the larger manufacturers also have higher-resolution devices, for example Teledyne LeCroy has its High Resolution Oscilloscope (HRO), which is a fixed 12-bit device.

Note that many devices will advertise either an “effective” or “software enhanced” bit resolution higher than the actual ADC resolution. Be careful with this: software enhancement is done via filtering, and you need to be aware of the possible resulting changes to your measurement bandwidth. Two resources with more details on this mode include the ECN magazine article “How To Get More than 8 Bits from Your 8-bit Scope” and the Teledyne LeCroy application note “Enhanced Resolution.” Remember that a 12-bit, 100-MHz bandwidth oscilloscope is not the same as an 8-bit, 100-MHz bandwidth oscilloscope with resolution enhancement!

Using the oscilloscope’s fast Fourier transform (FFT) mode (normally advertised as the spectrum analyzer mode), we can see the difference a higher-resolution ADC makes. When looking at a waveform on the screen, you may think that you don’t care at all about 14-bit accuracy or something similar. However, if you plan to do measurements such as total harmonic distortion (THD), or otherwise need accurate information about frequency components, having high resolution may be extremely important to achieve a reasonable dynamic range.

As a theoretical example I’m using my script mentioned earlier, which will digitize a perfect sine wave and then display the frequency spectrum. The number of bits in the ADC (e.g., quantization) is adjustable, so the harmonic component is solely due to quantization error. This is shown in Figure 4. If you want to see a version of this using a real instrument, I conduct a similar demonstration in this video.

Certain applications may find the higher bit resolution a necessity. For example, if you are working in high-fidelity audio applications, you won’t be too worried about an extremely high sample rate, but you will need the high resolution.

Figure 4: In the frequency domain, the effect of limited quantization bits is much more apparent. Here a 10-MHz pure sine wave frequency spectrum is taken using a different number of bits during the quantization process.

Figure 4: In the frequency domain, the effect of limited quantization bits is much more apparent. Here a 10-MHz pure sine wave frequency spectrum is taken using a different number of bits during the quantization process. (CLICK TO ZOOM)

Coming Up
This week I’ve taken a look at some of the core specifications. I hope the questions to ask when purchasing an oscilloscope are becoming clearer! Next week, I’ll be looking at the software running the oscilloscope, and details such as remote control, FFT features, digital decoding, and buffer types. The fourth and final week will delve into a few remaining features such as external trigger and clock synchronization and will summarize all the material I’ve covered in this series.

Author’s note: Every reasonable effort has been made to ensure example specifications are accurate. There may, however, be errors or omissions in this article. Please confirm all referenced specifications with the device vendor.

Evaluating Oscilloscopes (Part 1)

Recently, I was in the market for a new oscilloscope. There’s a good selection of devices for sale, but which should you choose? It’s clear from the ads that the “scope bandwidth” and “sample rate” are two important parameters. But are there other things hidden in the specification sheet you should take a look at?

I’ve compiled notes from my own oscilloscope-selection experience and wanted to share them with you. I’ll be pulling in specifications and examples from a few different oscilloscopes. Personally, I ended up selecting a PicoScope device, so I will be featuring it more prominently in my comparisons. But that’s simply because I don’t have a lab full of oscilloscopes to photograph! I don’t work for Pico Technology or have any affiliation with it, and will be attempting to pull in other manufacturers for this online series to provide some balance.

This “mini-series” will consist of four posts over four weeks. I won’t be discussing bandwidth and sample rate until next week. In this first post, I’ll cover some physical characteristics: stand-alone vs PC-based probe types and digital inputs. Next week I’ll discuss the “core” specifications, in particular the bandwidth, sample rate, and analog-to-digital converter resolution. The  third week will look at the software running the oscilloscope, and details such as remote control, fast Fourier transform (FFT) features, digital decoding, and buffer types. The final week will consider a few remaining features such as the external trigger and clock synchronization, and will summarize all the material I’ve covered.

I hope you find it useful!

Topic 1: Do You Want a PC-Based or Stand-Alone Instrument?
There are two fundamentally different types of instruments, and you’ll have to decide for yourself which you prefer. Many people like a stand-alone instrument, which you can place on your bench and probe your circuits to your heart’s content. You don’t need to have your computer nearby, and you have something solely dedicated to probing.

Figure 1: PC-based oscilloscopes make it easier to mount on a crowded bench. This PicoScope 6000 unit is velcroed to my desk, you can see the computer monitor to the upper left.

Photo 1: PC-based oscilloscopes make mounting easier on a crowded bench. This PicoScope 6000 unit is velcroed to my desk. You can see the computer monitor to the upper left.

The other option is a PC-based instrument, which today generally means it plugs in via USB. I’ve always preferred this type for a few reasons. The first is the minimal desk space needed. I can place an oscilloscope vertically and lose little space (see Photo 1). The second is I find it easier to interact with a standard keyboard and mouse, especially if you’re using more advanced features. In addition, you can easily save screenshots or data from the scope without having to transfer them using a USB key or something similar.

There are a few downsides to USB-based instruments. The most common complaint is probably the lack of knobs, although that’s fixable. In Photo 2, you can see a USB-based “knob board” I built, which pretends to be a USB key. Each turn of the knob sends a keystroke and, as long as your PC-based oscilloscope software lets you set custom keyboard shortcuts, can trigger features such as changing the input range or timebase. Most of the time, I still just use the regular PC interface, as I find it easier than knobs. If you’re interested in the design, you can find it on my blog Electronics & More.

Photo: A simple USB-based knob board uses mechanical encoders to control the USB scope via a physical panel.

Photo 2: A simple USB-based knob board uses mechanical encoders to control the USB scope via a physical panel.

Having a PC-based oscilloscope also means you can have a massive screen. A high-end oscilloscope will advertise a “large 12.1″ screen,” but you can purchase a 22″ screen for your computer for $200 or less.  If your PC-based oscilloscope software supports multiple “viewports,” you can more easily set up complex displays such as that in Figure 1.
Again this comes down to personal preference—personally, I like having the oscilloscope display as a window on my computer. You may wish to have a dedicated display separate from your other work, in which case consider a stand-alone device!

Figure 1: PC-based oscilloscopes make it easier for setting up windows in specific positions, due to a combination of much larger screen space and standard mouse/keyboard interaction.

Figure 1: PC-based oscilloscopes make it easier for setting up windows in specific positions, due to a combination of much larger screen space and standard mouse/keyboard interaction.

Topic 2: Where’s the Ground?
One common complaint with the PC-based oscilloscope is that the probe ground connects to USB ground. Thus, you need to ensure there isn’t a voltage difference between the ground of your device under test and the computer.

This is, in fact, a general limitation of most oscilloscopes, be they stand-alone or PC-based. If you check with an ohmmeter, you’ll generally find that the ”probe ground”  in fact connects to system Earth on stand-alone oscilloscopes. Or at least it did on the different Agilent units I tested. Thus the complaint is somewhat unfairly leveled at PC-based devices.

You can get oscilloscopes that have either “differential” or “isolated” inputs, which are designed to eliminate the problem of grounds shorting out between different inputs. They may also give you more measurement flexibility. For example, if you are trying to measure the voltage across a “high-side shunt resistor,” you can do this measurement differentially. The TiePie engineering  HS4 DIFF is one example of a device with this capability. Of course, you can purchase differential probes for any oscilloscope, which accomplish the same goal! Most manufactures make these differential probes (Agilent, Tektronix, Pico Technology, Rigol, etc.).

Topic 3: Input Types
Almost every scope will have either DC-coupled or AC-coupled inputs. You’ll likely want to compare the minimum/maximum voltage ranges the scope has. Don’t be too distracted by either the upper or lower limits unless you have very specific requirements. At the upper end, remember you will mostly be using the 10:1 probe, which means an oscilloscope with ±20 V input range becomes ±200 V with the 10:1 probe.

At the lower end, the noise is going to kill you. If your oscilloscope has a 1 mV/div range, for example, you’ll have to be extremely careful with noise. To probe very small signals, you’ll probably end up needing an active probe with amplification right at the measurement point. This can be something you build yourself, using a differential amplifier chip, for example, if you are attempting to measure current across a shunt.

Besides the actual measurement range, you’ll be interested in the “offset” range too. With the DC-input, most oscilloscopes can subtract a fixed voltage from the input. Thus you can measure a 1.2-V input on a 1-V maximum input range, as the oscilloscope is able to first subtract say 1 V from the signal. This is handy if you have a smaller signal riding on top of some fixed voltage.

Another input type you will encounter is the 50-Ω input. Normally, this means the oscilloscope can switch between AC, DC, and DC 50 input types. The DC 50 means the input is “terminated” with a 50-Ω impedance. This feature is typically found on oscilloscopes with higher analog bandwidth. For example, this allows you to measure a clock signal that is output on a SMA connector expecting a 50-Ω termination. In addition, the 50-Ω input allows you to simplify connection of other lab equipment to your oscilloscope. Want to use a low noise amplifier (LNA) to measure a very small signal? Not a problem, since you can properly terminate the output of that LNA.

If you end up needing DC 50 termination, you can buy “feed-through” terminators for about $15, which operate at up to 1-GHz bandwidth. You simply add those to the front of your oscilloscope to get 50-Ω terminated inputs.

Any given manufacturer will often have a range of inputs for different bandwidths and models. For example, the PicoScope 5000-series, which has up to 200-MHz bandwidth, has DC/AC high-impedance inputs. The 6000-series has DC/AC/DC 50 inputs for 500-MHz bandwidth and below. The 6000 series in 1,000 MHz bandwidth only has 50-Ω input impedance. Other manufacturers seem to follow a similar formula: the highest bandwidth device is 50-Ω input only, medium-bandwidth devices are DC/AC/DC 50, and lower-bandwidth devices will be DC/AC.

Topic 4: Probe Quality and Type
In day-to-day use, nothing will impact you more than the quality of your oscilloscope probe. This is your hands-on interaction with the oscilloscope.

Figure 4: A smaller spring-loaded probe tip is on the left,  and  a standard oscilloscope probe is on the right. Both  probes have removable tips, so if you damage the probe it’s easy to fix them. Not all probes have removable tips, however, meaning if the tip is damaged you may have to throw out the probe.

Photo 3: A smaller spring-loaded probe tip is on the left, and a standard oscilloscope probe is on the right. Both probes have removable tips, so if you damage the probe it’s easy to fix them. Not all probes have removable tips, however, meaning if the tip is damaged you may have to throw out the probe.

Most “standard” oscilloscope probes are of the type pictured to the right in Photo 3. They are normally switchable from 1:1 to 10:1 attenuation, where the 10:1 mode results in a 1/10 scaling of input voltage. It’s important to note that almost every oscilloscope probe has very limited bandwidth in 1:1 mode—often under 10 MHz. Whereas in 10:1 mode it might be 300 MHz! In addition, the 10:1 mode will load the circuit considerably less. Higher bandwidth probes will often only come in 10:1 mode. I assume the physical switch is too much hassle at higher frequencies!

A first thing to check out is if the tip is removable. If you damage the tip, it can be useful to simply replace the tip rather than the entire probe. If you’re probing a PCB, it can be easy to catch a tip in a via, for example. Alternatively, certain probes might come with an adapter, which is designed for use in probing the PCB, rather than just the tip of the regular oscilloscope probe. The older Agilent 1160A probes come with such a tip.

One particular type of probe I really like has the spring-loaded tip shown to the left in Photo 3. This is a much smaller tip than “standard,” and the spring-loaded tip makes it much easier to get a good connection with solder joints. You can apply some pressure to break through the oxide layer, and the spring-loaded aspect keeps the tip right on the joint. In addition, you can even do things such as probe through the solder mask on a via. There are even plastic guard add-ons, which fit standard surface mount device (SMD) sizes (e.g., 1.27 mm, 1 mm, 0.8 mm, 0.5 mm) to probe TQFP/SOIC/TSSOP packages.

The particular probe I’m photographing comes with the PicoScope 6000 series, which is sold separately as part number TA150 (350-MHz bandwidth) or TA133 (500-MHz bandwidth). However, I’ve noticed that Agilent seems to also sell a probe that looks the same—under part number N287xA—right down to accessories. Similarly, Teledyne LeCroy also seems to sell this probe under the PP007 part number, and Rohde & Schwarz sells it under the RTM-ZP10 part number, also with the same accessories. Thus I suspect there is some upstream manufacturer! Depending on your supplier and options, prices range from $200-$400 for the probe if you want to pick it up separately.

Photo 5: The ground spring accessory can be used in a number of ways. If you're lucky, you can insert it into GND  vias on your PCB. If required, you can also solder a small section of wire to the spring.

Photo 4: The ground spring accessory can be used in a number of ways. If you’re lucky, you can insert it into GND vias on your PCB. If required, you can also solder a small section of wire to the spring.

Pomona Electronics sells a similar probe, part numbers 6491 through 6501 (the exact partnumber depending on bandwidth). The 150-MHz version (6493) is available for under $60 from Digi-Key, Mouser, and Newark element14, for example. This probe differs from the previous group of spring-loaded ones, but if you don’t need the higher bandwidth it may be a more reasonable purchase.

If you are dealing with a high-bandwidth probe, you may need to be concerned about the flatness of the frequency response. A probe may be sold with a 1G-Hz bandwidth, for example, which simply means the -3-dB point is at 1GHz. However, shoddy manufacturing may mean not having a very flat frequency response before that point, or not rolling off evenly after the -3-dB point.

When dealing with high bandwidth probes, the grounding will become a serious issue. The classic “alligator clip” probably won’t cut it anymore! The simplest accessory your probe is likely to come with is the spring adapter shown in Photo 4. There may be more advanced accessories available for grounding, too; check documentation for the probe itself. You can see an example of differences in grounding as part of my “probe review”  video.

Don’t be afraid to build your own accessories for the probe. Photo 5 shows a probe holder I built for a $15 adjustable arm. Details of the construction are here.

Here’s a simple 3-D probe holder you can build for $20 or less.

Photo 5: Here’s a simple 3-D probe holder you can build for $20 or less.

Topic 5: Digital Input?
The final item to consider is if you want digital inputs along with analog. This is, again, somewhat of a personal choice: You may wish to have a separate stand-alone digital analyzer, or you may wish to have it built into your oscilloscope.

I personally chose to have a stand-alone digital logic analyzer, which is a PC-based instrument. Digital logic analyzers are available at a fairly low cost from a variety of manufacturers (e.g., Saleae and Intronix). In my experience, the cost of purchasing a separate PC-based logic analyzer was considerably lower than the “incremental cost” of selecting an oscilloscope with logic analyzer capabilities compared to one without. When evaluating this yourself, be sure to look at features such as number of channels, maximum sample rate, buffer size, and what protocols can be decoded by the logic analyzer.

While integrated-device manufacturers claim you should buy a scope/analyzer in one unit to get perfect synchronization between digital and analog, remember many of these devices can output a trigger signal. So if your oscilloscope can output a trigger signal when it starts the analog capture, you can use this to capture the corresponding data on the digital logic analyzer (or vice versa).

Next Week: Core Specifications
This first week I covered physical details of the oscilloscope itself you might want to consider. Next week, I’ll look at the more ‘”core” specifications such as bandwidth, sample rate, and sample resolution.

Author’s note: Every reasonable effort has been made to ensure example specifications are accurate. There may, however, be errors or omissions in this article. Please confirm all referenced specifications with the device vendor.


MCU-Based Projects and Practical Tasks

Circuit Cellar’s January issue presents several microprocessor-based projects that provide useful tools and, in some cases, entertainment for their designers.

Our contributors’ articles in the Embedded Applications issue cover a hand-held PIC IDE, a real-time trailer-monitoring system, and a prize-winning upgrade to a multi-zone audio setup.

Jaromir Sukuba describes designing and building the PP4, a PIC-to-PIC IDE system for programming and debugging a Microchip Technology PIC18. His solar-powered,

The PP4 hand-held PIC-to-PIC programmer

The PP4 hand-held PIC-to-PIC programmer

portable computing device is built around a Digilent chipKIT Max32 development platform.

“While other popular solutions can overshadow this device with better UI and OS, none of them can work with 40 mW of power input and have fully in-house developed OS. They also lack PP4’s fun factor,” Sukuba says. “A friend of mine calls the device a ‘camel computer,’ meaning you can program your favorite PIC while riding a camel through endless deserts.”

Not interested in traveling (much less programming) atop a camel? Perhaps you prefer to cover long distances towing a comfortable RV? Dean Boman built his real-time trailer monitoring system after he experienced several RV trailer tire blowouts. “In every case, there were very subtle changes in the trailer handling in the minutes prior to the blowouts, but the changes were subtle enough to go unnoticed,” he says.

Boman’s system notices. Using accelerometers, sensors, and a custom-designed PCB with a Microchip Technology PIC18F2620 microcontroller, it continuously monitors each trailer tire’s vibration and axle temperature, displays that information, and sounds an alarm if a tire’s vibration is excessive.  The driver can then pull over before a dangerous or trailer-damaging blowout.

But perhaps you’d rather not travel at all, just stay at home and listen to a little music? This issue includes Part 1 of Dave Erickson’s two-part series about upgrading his multi-zone home audio system with an STMicroelectronics STM32F100 microprocessor, an LCD, and real PC boards. His MCU-controlled, eight-zone analog sound system won second-place in a 2011 STMicroelectronics design contest.

In addition to these special projects, the January issue includes our columnists exploring a variety of  EE topics and technologies.

Jeff Bachiochi considers RC and DC servomotors and outlines a control mechanism for a DC motor that emulates a DC servomotor’s function and strength. George Novacek explores system safety assessment, which offers a standard method to identify and mitigate hazards in a designed product.

Ed Nisley discusses a switch design that gives an Arduino Pro Mini board control over its own power supply. He describes “a simple MOSFET-based power switch that turns on with a push button and turns off under program control: the Arduino can shut itself off and reduce the battery drain to nearly zero.”

“This should be useful in other applications that require automatic shutoff, even if they’re not running from battery power,” Nisley adds.

Ayse K. Coskun discusses how 3-D chip stacking technology can improve energy efficiency. “3-D stacked systems can act as energy-efficiency boosters by putting together multiple chips (e.g., processors, DRAMs, other sensory layers, etc.) into a single chip,” she says. “Furthermore, they provide high-speed, high-bandwidth communication among the different layers.”

“I believe 3-D technology will be especially promising in the mobile domain,” she adds, “where the data access and processing requirements increase continuously, but the power constraints cannot be pushed much because of the physical and cost-related constraints.”

A Look at Low-Noise Amplifiers

Maurizio Di Paolo Emilio, who has a PhD in Physics, is an Italian telecommunications engineer who works mainly as a software developer with a focus on data acquisition systems. Emilio has authored articles about electronic designs, data acquisition systems, power supplies, and photovoltaic systems. In this article, he provides an overview of what is generally available in low-noise amplifiers (LNAs) and some of the applications.

By Maurizio Di Paolo Emilio
An LNA, or preamplifier, is an electronic amplifier used to amplify sometimes very weak signals. To minimize signal power loss, it is usually located close to the signal source (antenna or sensor). An LNA is ideal for many applications including low-temperature measurements, optical detection, and audio engineering. This article presents LNA systems and ICs.

Signal amplifiers are electronic devices that can amplify a relatively small signal from a sensor (e.g., temperature sensors and magnetic-field sensors). The parameters that describe an amplifier’s quality are:

  • Gain: The ratio between output and input power or amplitude, usually measured in decibels
  • Bandwidth: The range of frequencies in which the amplifier works correctly
  • Noise: The noise level introduced in the amplification process
  • Slew rate: The maximum rate of voltage change per unit of time
  • Overshoot: The tendency of the output to swing beyond its final value before settling down

Feedback amplifiers combine the output and input so a negative feedback opposes the original signal (see Figure 1). Feedback in amplifiers provides better performance. In particular, it increases amplification stability, reduces distortion, and increases the amplifier’s bandwidth.

 Figure 1: A feedback amplifier model is shown here.

Figure 1: A feedback amplifier model is shown.

A preamplifier amplifies an analog signal, generally in the stage that precedes a higher-power amplifier.

Op-amps are widely used as AC amplifiers. Linear Technology’s LT1028 or LT1128 and Analog Devices’s ADA4898 or AD8597 are especially suitable ultra-low-noise amplifiers. The LT1128 is an ultra-low-noise, high-speed op-amp. Its main characteristics are:

  • Noise voltage: 0.85 nV/√Hz at 1 kHz
  • Bandwidth: 13 MHz
  • Slew rate: 5 V/µs
  • Offset voltage: 40 µV

Both the Linear Technology and Analog Devices amplifiers have voltage noise density at 1 kHz at around 1 nV/√Hz  and also offer excellent DC precision. Texas Instruments (TI)  offers some very low-noise amplifiers. They include the OPA211, which has 1.1 nV/√Hz  noise density at a  3.6 mA from 5 V supply current and the LME49990, which has very low distortion. Maxim Integrated offers the MAX9632 with noise below 1nV/√Hz.

The op-amp can be realized with a bipolar junction transistor (BJT), as in the case of the LT1128, or a MOSFET, which works at higher frequencies and with a higher input impedance and a lower energy consumption. The differential structure is used in applications where it is necessary to eliminate the undesired common components to the two inputs. Because of this, low-frequency and DC common-mode signals (e.g., thermal drift) are eliminated at the output. A differential gain can be defined as (Ad = A2 – A1) and a common-mode gain can be defined as (Ac = A1 + A2 = 2).

An important parameter is the common-mode rejection ratio (CMRR), which is the ratio of common-mode gain to the differential-mode gain. This parameter is used to measure the  differential amplifier’s performance.

Figure 2: The design of a simple preamplifier is shown. Its main components are the Linear Technology LT112 and the Interfet IF3602 junction field-effect transistor (JFET).

Figure 2: The design of a simple preamplifier is shown. Its main components are the Linear Technology LT1128 and the Interfet IF3602 junction field-effect transistor (JFET).

Figure 2 shows a simple preamplifier’s design with 0.8 nV/√Hz at 1 kHz background noise. Its main components are the LT1128 and the Interfet IF3602 junction field-effect transistor (JFET).  The IF3602 is a dual Nchannel JFET used as stage for the op-amp’s input. Figure 3 shows the gain and Figure 4 shows the noise response.

Figure 3: The gain of a low-noise preamplifier.

Figure 3: The is a low-noise preamplifier’s gain.


Figure 4: The noise response of a low-noise preamplifier

Figure 4: A low-noise preamplifier’s noise response is shown.

The Stanford Research Systems SR560 low-noise voltage preamplifier has a differential front end with 4nV/√Hz input noise and a 100-MΩ input impedance (see Photo 1a). Input offset nulling is accomplished by a front-panel potentiometer, which is accessible with a small screwdriver. In addition to the signal inputs, a rear-panel TTL blanking input enables you to quickly turn the instrument’s gain on and off (see Photo 1b).

Photo 1a:The Stanford Research Systems SR560 low-noise voltage preamplifier

Photo 1a: The Stanford Research Systems SR560 low-noise voltage preamplifier. (Photo courtesy of Stanford Research Systems)

Photo 1 b: A rear-panel TTL blanking input enables you to quickly turn the Stanford Research Systems SR560 gain on and off.

Photo 1b: A rear-panel TTL blanking input enables you to quickly turn the Stanford Research Systems SR560 gain on and off. (Photo courtesy of Stanford Research Systems)

The Picotest J2180A low-noise preamplifier provides a fixed 20-dB gain while converting a 1-MΩ input impedance to a 50-Ω output impedance and 0.1-Hz to 100-MHz bandwidth (see Photo 2). The preamplifier is used to improve the sensitivity of oscilloscopes, network analyzers, and spectrum analyzers while reducing the effective noise floor and spurious response.

Photo 2: The Picotest J2180A low-noise preamplifier is shown.

Photo 2: The Picotest J2180A low-noise preamplifier is shown. (Photo courtesy of picotest.com)

Signal Recovery’s Model 5113 is among the best low-noise preamplifier systems. Its principal characteristics are:

  • Single-ended or differential input modes
  • DC to 1-MHz frequency response
  • Optional low-pass, band-pass, or high-pass signal channel filtering
  • Sleep mode to eliminate digital noise
  • Optically isolated RS-232 control interface
  • Battery or line power

The 5113 (see Photo 3 and Figure 5) is used in applications as diverse as radio astronomy, audiometry, test and measurement, process control, and general-purpose signal amplification. It’s also ideally suited to work with a range of lock-in amplifiers.

Photo 3: This is the Signal Recovery Model 5113 low-noise pre-amplifier.

Photo 3: This is the Signal Recovery Model 5113 low-noise preamplifier. (Photo courtesy of Signal Recovery)

Figure 5: Noise contour figures are shown for the Signal Recovery Model 5113.

Figure 5: Noise contour figures are shown for the Signal Recovery Model 5113.

This article briefly introduced low-noise amplifiers, in particular IC system designs utilized in simple or more complex systems such as the Signal Recovery Model 5113, which is a classic amplifier able to obtain different frequency bands with relative gain. A similar device is the SR560, which is a high-performance, low-noise preamplifier that is ideal for a wide variety of applications including low-temperature measurements, optical detection, and audio engineering.

Moreover, the Krohn-Hite custom Models 7000 and 7008 low-noise differential preamplifiers provide a high gain amplification to 1 MHz with an AC output derived from a very-low-noise FET instrumentation amplifier.

One common LNA amplifier is a satellite communications system. The ground station receiving antenna will connect to an LNA, which is needed because the received signal is weak. The received signal is usually a little above background noise. Satellites have limited power, so they use low-power transmitters.

Telecommunications engineer Maurizio Di Paolo Emilio was born in Pescara, Italy. Working mainly as a software developer with a focus on data acquisition systems, he helped design the thermal compensation system (TCS) for the optical system used in the Virgo Experiment (an experiment for detecting gravitational waves). Maurizio currently collaborates with researchers at the University of L’Aquila on X-ray technology. He also develops data acquisition hardware and software for industrial applications and manages technical training courses. To learn more about Maurizio and his expertise, read his essay on “The Future of Data Acquisition Technology.”

DC Motor for Fine Rotary Motions

The RE 30 EB precious metal brushed motor features a low start-up voltage, even after a long period in standstill. With a 53-mNm rated torque, the powerful motor provides twice the power of an Maxon RE 25 EB. In addition, the RE 30 EB features minimal high-frequency interference.

The RE 30 EB motor is specifically designed for haptic applications (e.g., surgical robots). Therefore, the motor can also be used as a highly sensitive sensor, acting as the sense of touch to register mechanical resistance.

Contact Maxon for pricing.

Maxon Precision Motors

Dual-Display Digital Multimeter

The DM3058E digital multimeter (DMM) is designed with 5.5-digit resolution and dual display. The DMM can enable system integration and is suitable for high-precision, multifunction, and automatic measurement applications.

The DM3058E is capable of measuring up to 123 readings per second. It can quickly save or recall up to 10 preset configurations, including built-in cold terminal compensation for thermocouples.

The DMM provides a convenient and flexible platform with an easy-to-use design and a built-in help system for information acquisition. In addition, it supports 10 different measurement types including DC voltage (200 mV to approximately 1,000 V), AC voltage (200 mV to approximately 750 V), DC current (200 µA to approximately
10 A), AC current (20 mA to approximately 10 A), frequency measurement (20 Hz to approximately 1 MHz), 2-Wire and 4-Wire resistance (200 O to approximately 100 MO), and diode, continuity, and capacitance.

The DM3058 is ideal for research and development labs and educational applications, as well as low-end detection, maintenance, and quality tests where automation combined with capability and value are needed.

The DM3058E digital multimeter costs $449.

Rigol Technologies, Inc.