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Review by Nicholas Vinen Rohde & Schwarz RTM3004 Mixed Signal Oscilloscope Until recently, unless you had a lot of money to spend, you had to decide whether you wanted a scope with good vertical resolution and low noise (for examining low-level signals) or high-speed performance (for highfrequency or rapidly changing signals). Now you can have both, with the Rohde & Schwarz RTM3004. I f you have seen the recent ads from Rohde & Schwarz, you will have noticed that they have released a number of new scopes and that most of them share a single distinguishing feature: their use of a 10-bit analog-to-digital converter (ADC) for better vertical resolution. Typical digital scopes use an 8-bit high-speed ADC. That means they can sense 28 or 256 different voltage levels in any given range. The 10-bit ADC used in many of the latest Rohde 36 Silicon Chip & Schwarz scopes has 1024 distinct voltage steps – a significant increase. This is especially useful when you consider that your standard highbandwidth oscilloscope probe has a 10:1 division ratio. This is necessary to allow the probe to be properly compensated so that it has a reasonably flat frequency response up to the scope's -3dB point (ie, its rated bandwidth). So if you're probing a 100mV signal with the standard set of probes, you get just 10mV at the input connector. Celebrating 30 Years If the original signal amplitude is already low and the scope has an 8-bit ADC, you may get a very small “jagged” trace, so it can be difficult to make out the shape of the signal. With a 10bit ADC, you have four times as many steps and the waveform shape is much clearer and cleaner, as you will notice in our screen grabs. However, a scope’s own noise is also an issue when examining low-level signals. The RTM3004 has a slightly better-than-average noise level, so you siliconchip.com.au Fig.1: each trace shows one of the pattern generator outputs, set to produce a rolling binary counter incremented at 10MHz. Here you can see the five different bandwidth options that were selectable for each channel of our 500MHz bandwidth demo scope. can often take advantage of the extra vertical resolution. But sometimes the noise still gets in the way. Five different bandwidth limiting options were provided on the 500MHz model we tested, from 20MHz up to the full 500MHz. That lets you choose a good tradeoff between bandwidth and noise, depending on the signal you are measuring (see Fig.1). This is a welcome feature. In terms of waveform capture rate, the RTM3004 compares well with its competitors, handling up to 64,000 waveforms per second at up to five gigasamples per second. It also has a very large 40Mpoints per channel of memory depth. You can expand that to 80Mpoints on the 4-channel model, if you're only using two channels. That’s truly massive and you can capture data on a long time-scale and then zoom right in to see the details. First impressions Besides the high vertical resolution, one of the first things we noticed when switching on the scope is that coming out of standby and into full operation only takes about ten seconds; quite a bit faster than some of the other scopes we've used. It's also very quiet during operation, with barely audible fan noise. Another nice feature of this scope is the high-resolution touchscreen. It's very sharp and clear and you can see a lot of detail in the traces and labels. But it lacks an anti-glare coating, so you can see your reflection on the siliconchip.com.au Fig.2: this demonstrates that you can have up to eight userconfigurable measurements at the bottom of the screen, in this case, peak-to-peak voltage and frequency for each channel. Colour coding helps easily identify which measurement is for which channel. screen, along with whatever happens to be behind you (a window etc). That can make it harder to make out the actual display. But if you use it in a dimly lit room, it's very good. This unit makes good use of the large amount of screen space available on the 1280 x 800 pixel, 10-inch (25cm) display. Most of the screen is filled with the graticule, giving the maximum amount of space for traces. Menus pop out as necessary but you can easily make them disappear to get the screen real estate back. The wide aspect works well, giving twelve time divisions and 10 voltage divisions. Measurements The RTM3004 lets you put eight measurements of your choice at the bottom of the screen. Far better than the four or five of most other scopes. This may seem like a minor point but when you’re using all four inputs, it can be a godsend (see Fig.2). Measurements are chosen from a menu of clear icons (Fig.3). It's a small thing but it's one of our favourite features of this scope. A bonus measurement feature is that each measurement can be "gated" within a specified time period so that the result only depends on the values within that time period. The time period can be defined as any subset of the 12 graticules shown on the display, based on either percentage or time delay and each measurement can be based either on the gating period or the full screen. Celebrating 30 Years When using gating, a blue highlighted box appears behind the traces for that period, so you can see how the measurements relate to the traces on the display (see Fig.4). Illuminated buttons The colour-changing illuminated buttons on this scope are a great idea. The vertical controls (voltage range, etc) change colour to match the colour coding of the currently selected channel. Similarly, the trigger source button colour matches the channel which is currently being used as the trigger source. Pressing that button cycles the trigger source through the available channels too. But the default brightness of the illuminated buttons is quite dazzling. Happily, the menus provide the ability for you to adjust the button brightness. And at the minimum setting of 20%, they're a lot less dazzling in anything but the most brightly lit workspace. It's a pity that you can't turn them down lower because a setting of 10% would probably be ideal in our office. At 20%, the contrast between the lit and unlit buttons makes it hard to read the labels on the unlit buttons. Now, on any DSO, when you have the trigger mode set to "normal" (not "auto"), it's quite common for the scope to stop triggering if the input signals change. And if you had a steady signal up to that point, it won’t be immediately obvious that the scope is no longer triggering and updating its screen. But Rohde & Schwarz have added a timer near the upper-right corner of April 2018  37 Fig.3: one of four menus showing the available measurements. The menu at right shows that you can select a measurement position (1-8), measurement type (from the menu), source channel, whether to use the gating period and whether to display statistics (max/min/average). the screen. When triggering normally, this area reads "Trig" but if triggering stops, it changes to read "Trig? 1s" and the time counts up. So it’s obvious that triggering has stopped and you can see at a glance how long the display has been static. It's a small feature but one we found ourselves using quite often. User interface Overall, we'd have to say that the user interface on this scope is probably the easiest that we have used and is very intuitive. That's largely because Rohde & Schwarz have abandoned the idea that all functions need to be available via dedicated buttons and you now need to use the touchscreen for many operations. Fig.4: any set of (or all) measurements can be “gated” by a time period which is a subset of the current period being displayed by the scope. This is the area shown in blue and it can be defined as either a proportion of the display or by the start and end delay, as shown here. That means they were able to simplify the button layout and it also makes it a lot more obvious how to carry out most tasks. The tradeoff is that you will probably need to clean your fingerprints off the screen regularly. But that's a small amount of extra effort in exchange for making the scope easier to use. One more nice aspect of the interface is the "toolbar" at upper left, with icons giving you access to commonly used functions. There's a small settings button at top-middle which lets you select which icons appear in this toolbar (see Fig.5). This allows you to populate the interface with buttons to features you frequently use. One small criticism that we have of the user interface is that it has unnecessary animations when you press buttons. For example, the menu at the righthand side of the screen "slides" in and out. That takes time and we’re often ready to press a button before it's actually visible. It would be nice to have the option to be able to turn off animations, to make the interface a bit more snappy. While the interface is quite responsive, there are occasions when there is a short delay between pressing a control and having it take effect. It isn't a big problem but it does fall slightly short of our expectations for the responsiveness of a high-end scope. The USB and Ethernet control sockets are on the back, plus power and an auxilliary output. The 16 digital inputs are on the right side of the scope, which is convenient since it means the ribbon cables don’t get in the way in mixed signal mode. 38 Silicon Chip Celebrating 30 Years siliconchip.com.au Fig.5: these icons can be displayed on the “toolbar” at upper left so that you can select the option at any time. The currently visible icons are shown in blue and as indicated on-screen, you can have up to eight shown. This menu is accessed using the button just above the yellow trigger marker. Options The RTM3004 has a number of extra cost software and hardware options which can add features to the scope. Besides the bandwidth (upgradeable to 1GHz) and 16-channel logic analyser (MSO) option, these include serial triggering and decoding for a range of protocols, history and segmented memory, spectrum analysis, power analysis and an arbitrary waveform/pattern generator. The configuration menu for the pattern generator is shown in Fig.6. Some of these options (eg, the pattern generator and power analysis) provide built-in “apps” which can be launched when needed. A number of these options, including all the serial decoding/ Fig.6: configuration for the pattern generator option. Like most aspects of the scope, when you’re adjusting its settings, the menu pops out from the right-hand side of the screen. When finished, it can be hidden simply by pressing the “menu” button in the lower right-hand corner. triggering options, history/segmented memory, spectrum analysis, power analysis and generators can be purchased in a bundle (RTM-PK1) which costs a lot less than paying for each option individually. The pattern generator is quite useful, especially in combination with the serial decoding and triggering options as it can be used to generate serial test data, eg, to send to a DAC. You could then use the scope to observe the corresponding DAC output. Other features We don’t have space in this review to list all the other features of the scope. It has pretty much everything else that you would expect (or can think of, really). It supports mask and limit testing, segmented memory, digital voltmeter, probe sensing, active probes, external triggering and so on. Check the Rohde & Schwarz website for more information on the scope and all its features (www.rohde-schwarz. com/au/product/rtm3000). Conclusion If you are in the market for a fullyfeatured scope with a bandwidth up to 1GHz, the Rohde & Schwarz RTM3004 is well worth considering – especially if you’re keen to get an instrument that’s easy to drive. For more details, see the Rohde & Schwarz Australia website at www. rohde-schwarz.com/au/ For pricing or to order a scope, phone (02) 8874 5100 or email sales. SC australia<at>rohde-schwarz.com Features • • • • • • • • • siliconchip.com.au 10.1-inch 1280 x 800 touchscreen display Four analog and 16 optional digital channels Bandwidth: 100Mhz (upgradeable to a maximum of 1GHz) Sample rate: up to 5Gsamples/s Memory depth: 40Mpoints/ channel and up to 80Mpoints interleaved Wafeform capture rate: 64000/s 500µV/div maximum sensitivity at full bandwidth 10-bit ADC Connections: LAN, USB, Ethernet April 2018  39