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Review by Nicholas Vinen Rohde & Schwarz RTB2004 Mixed Signal Oscilloscope The key features of this four-channel mixed signal oscilloscope (MSO) are a 10-bit analog-to-digital converter (ADC) giving high vertical (voltage) resolution, a large high-resolution touch screen and a built-in four-channel pattern generator which is capable of producing various different kinds of serial test signals. This is in addition to the features you’d expect such as cursors, many different measurements, acquisition modes, trigger modes, logic decoding and so on. 22  Silicon Chip siliconchip.com.au T he RTB2004 is a four-channel digital oscilloscope with bandwidth options of 70MHz, 100MHz, 200MHz and 300MHz and a sampling rate of 1.25GSa/s per channel (2.5GSa/s maximum). It comes standard with a large 10 megasample (MSa) memory. Perhaps the most immediately striking feature is the 10.1-inch (25cm) glossy capacitive touchscreen which has a resolution of 1280 x 800 pixels. It allows for a clear trace and a lot of menus and read-outs on screen at once, plus a 12-grid horizontal graticule (compared to 10 for many other scopes). Buttons and knobs control the most common functions such as changing timebase, vertical scale and offset and accessing various menus. But digging through the menus and changing options is generally done via the touchscreen. This is good because it makes the interface much more intuitive and easy to learn compared to other scopes. Normally this would mean that you would need to clean the screen regularly to keep it smudge-free but having said that, its surface seems to be treated in such a way that it doesn’t build up finger grease nearly as fast as some other touchscreens. By the way, as well as having a high resolution (for an oscilloscope), it also has excellent colour saturation and contrast. Fig.1: the orange trace shows the output of the built-in arbitrary waveform generator when set to produce a 10MHz square wave, while the mauve trace shows the noise present in an unterminated input with no bandwidth limiting (at 1mV/div). This is very low for a 300MHz scope. Quick boot-up and quiet operation The time from switching on to being able to use the scope is a very quick six seconds; some modern digital scopes take 30 seconds or longer to boot up. It’s also very quiet when operating, with very little fan noise. But funnily there is a quite an annoying faint switchmode whine when it is switched off but powered (ie, in standby). We would be inclined to switch it off at the wall for that reason alone. After switching on, it is immediately apparent that the 10-bit ADC, combined with very quiet front-end amplifiers, provide this scope with an extremely low amount of residual noise. So low that, with 1:1 probes, signals under 1mV peak-to-peak should be observable. Even the best analog scopes could not do this. The screen grab of Fig.1 shows the output of the inbuilt waveform generator at top when set to produce a 10MHz square wave (a bit rounded at this frequency), along with an unterminated input channel below, with its full 300MHz of bandwidth in effect. This is in “sampling” mode, ie, without any extra noise reduction and as you can see, the residual noise is around 400µV peak-to-peak. Limiting the bandwidth on that channel to 20MHz (still unterminated) gives the result shown in the screen grab of Fig.2, with the noise reduced to around 200µV peak-topeak. You can reduce it further with averaging if you have a repetitive signal and a reliable trigger source. Note that the high resolution of the screen means there’s room to label the graticule grid on both axes, as you can see in both screen grabs; a very handy feature. Also, in Fig.2, you can see the input configuration menu near the right side of the screen. This is typical of the type of menu used to set up various aspects of the scope. Entries marked with a circular arrow can be changed by touching on that item, then rotating the knob located in the lower-right hand corner of the front panel (or in many cases, using the alternative on-screen keyboard). Before moving on, we should note the light weight of the siliconchip.com.au Fig.2: the same traces as shown in Fig.1 but this time with 20MHz bandwidth limiting enabled for the unterminated input. As you can see, this reduces the noise level even further. The input set-up menu is visible towards the righthand edge of the display. Fig.3: the measurement set-up menu shows you both the name and an illustration of each available measurement, which can be applied to any given channel. Up to four custom measurements can be shown at once. Note that this is one of four menus (see the tabs at top). A August ugust 2017  23 2017  23 Fig.4: the second custom measurement menu, this time showing vertical (voltage)-related measurements. Take a look at the menu to the right of the measurements, which allows you to choose which of the four “places” the measurement goes into and which channel is used. Fig.5: now we are showing the menu of horizontal (timebase) related measurements. To use the Phase and Delay measurements, you must select two channels. You can also enable “statistics” to track minimum/ maximum/average values for each measurement. Fig.6: alternatively, you can simply enable “quick measurements” for one channel in which case you’ll get a display like this. You immediately get the nine most commonly used measurements all shown at once for a single channel, along with some crosshair-type cursors. 24  Silicon Chip RTB2004 at 2.5kg which, combined with its compact size (especially accounting for the large screen) of 390 x 220 x 152mm, makes it easy to move around and set up. The compact size does lead to one fairly significant tradeoff which is that there is only one set of vertical knobs (scale and offset) for all four channels. However, cleverly, the knobs are backlit by coloured LEDs and these change to the same colour as the trace of the channel that they are currently controlling. This makes it much easier to use, compared to other scopes with shared knobs. The knob backlight colour even changes to suit the “math” or reference traces, if those are currently in use. Regarding those backlighting LEDs, which you can clearly see in the lead shot and appear on many of the other on/off buttons too; they are informative and look pretty but they are too bright and if you work in a dim environment, you might grow weary of them; in a well-lit room they are fine. Other great features The list of measurements available is comprehensive and well-organised, making picking among the available measurements easy. Figs.3, 4 & 5 show most (but not all) of the measurement type selection menus, along with the measurement configuration menu down the right-hand side. One particularly handy feature is “quick measurement” mode which is activated by a dedicated front-panel button and the results are shown in Fig.6. The average, +peak and -peak voltages are shown next to the trace, along with rise and fall times, with RMS voltage, period, frequency and peak-to-peak measurements shown below (alongside the pre-existing measurements which have been moved to the left). Pressing the quick measurement button a second time goes back to the normal trace display. We also really liked the four-channel built-in pattern generator. Fig.7 shows the set-up dialog which gives you the choice of a number of different serial buses and other patterns, lets you select the transmission speed and shows you which signal is available on each of the four front-panel connection points (P0-P3). Behind this, you can see that we’ve set up an I2C signal and hooked up the two relevant outputs to input channels 1 & 2. We’ve then set up I2C serial decoding on these channels. The decoded data is shown in mauve between the two traces (showing SCL [clock] in yellow and SDA [data] in green). The RTB2004 can decode two different serial buses at once, the same or different types. Fig.8 shows a different example. This time the pattern generator is set up to produce data in CANbus format. We’ve set up both protocol decoders as the same data is broadcast in non-inverted and inverted form simultaneously, and we are able to decode both using the two separate protocol decoders. You can see the protocol decoder set-up menu at the right side of the screen. Other outstanding features of the RTB2004 include an update rate of 50,000 waveforms per second, optional 16-channel 1.25GSa/s logic analyser, optional built-in 20MHz arbitrary waveform generator, 128kpoint FFT (see the photo on page 23), a 160MSa segmented memory option and standard 3-year warranty. It also has USB device and host ports, an Ethernet LAN port and a built-in web server for remote control. Our test unit was a mixed-signal type (MSO) so it includsiliconchip.com.au ed two 8-channel logic heads along with the four standard probe kits and power cord. Some niggles While we’ve had a lot of good things to say about this scope, it does have a couple of aspects which could possibly be improved. The most noticeable of these is in regards to the responsiveness of the user interface, and the scope overall. At times it responds instantly to button presses or knob rotation while at other times, it seems to pause before updating the screen. This means that it takes a little longer to perform some tasks and it can be a bit frustrating. The most annoying aspect is when it stops updating the trace periodically. Perhaps it needs a faster processor. We would like to see more trigger options. There don’t seem to be runt or pulse-width trigger option but it does have video and serial triggering options. The “math” modes seem a little limited too, comprising addition, subtraction, multiplication, division and the separate FFT mode (sometimes lumped in under “math” on other scopes). Finally, you can only view four normal measurements at a time; with a screen this size, it should be possible to fit more (and some scopes allow for at least five). And the interface for setting up the measurements is a little clunky and this ends up being a relatively time-consuming task, especially considering it’s a feature that is in constant use (in our experience, anyway). Fig.7: here we have set up the scope’s pattern generator to produce a 400kbit I2C serial signal and are monitoring the two outputs using scope channels 1 & 2. We have also enabled the protocol decoder and the decoded hexadecimal values are shown between the two traces. Conclusion Overall, this is a very capable scope and the best midrange unit we have used for looking at low-level signals. It’s also among the easiest scopes to learn how to use, especially given the fairly large range of powerful features. While many of the features are options, many features which would be options on other scopes are standard; for example, the large standard 20 or 10MSample memory. The optional software features are higher bandwidth (>70MHz), mixed signal mode, arbitrary waveform generator, serial decoding and triggering (three types), history and segmented memory. These features can be added during or after purchase. But while have noted some criticisms above, given the unit’s overall performance compared to its price, we consider the RTB2000 series to be good value and definitely worth looking at if you are in the market for a mid-range scope. For more information, visit the Rohde & Schwarz Australia website via siliconchip.com.au/l/aad3 or email Sales.australia<at>rohdeschwarz.com Alternatively, you can make a telephone enquiry by calling SC (02) 8874 5100. Fig.8: a similar set-up to Fig.7 but this time we have set the pattern generator to produce a CANbus (controller area network) serial signal, as used in many automobiles. This is also being decoded using the protocol decoder, along with the inverted signal which encodes the same data. There’s not much to the rear panel: a 230V fused IEC socket and switch plus a LAN and USB socket. All other controls, inputs, etc are on the front. siliconchip.com.au A August ugust 2017  25 2017  25