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By MAURO GRASSI Tektronix MSO2024 Mixed Signal Oscilloscope A 200MHz, 1GS/s 4/16-channel mixed-signal oscilloscope The Tektronix MS2024 is a compact mixed-signal oscilloscope that is suitable for a wide range of applications or educational use. It has four analog and 16 digital inputs, a sampling rate of 1Gs/s and an operating bandwidth up to 200MHz. It is very easy to use and does not take up a lot of valuable bench space. T HE 4-CHANNEL MSO2024 is the top of the Tek2000 range. Its ability to accept up to 16 digital inputs for debugging of logic applications makes it particularly attractive, especially since it is such a compact unit. The operating bandwidth of this model is 200MHz and this will be more than adequate for most applications, including audio, video and general assorted use. The high sampling rate 1GS/s (Gigasamples per second), allows a timebase speed of up to 2ns/div. And although some oscilloscopes share the sampling rate among the available channels, the MSO2024 achieves 1GS/s on all four channels at all times. When you first pick up this scope, it gives two impressions. First, it is quite wide but not very deep at 140mm 76  Silicon Chip and therefore it won’t take up a lot of bench space which tends to be at a premium in most labs and workshops. The second impression is the wide aspect ratio screen. The display is a 7-inch WQVGA (Wide Quarter VGA). A wide QVGA screen must have the same vertical resolution as a QVGA screen but its aspect ratio will be different to the standard 4:3. In this case, the display has a resolution of 480 x 234 pixels giving an aspect ratio close to 2:1. This allows you to get a good display showing several cycles of typical signals, something that’s not possible on a screen of lesser width. The LCD also has a simulated phosphor response, meaning the intensity of the pixels varies according to the time they are on. siliconchip.com.au Fig.1: a screen grab showing a typical menu. You can see what the soft buttons running vertically down the side of the screen do as their function is clearly indicated adjacent to them on the screen. This sub menu gives the options for displaying the background grid. The intensity of the grid can also be changed using one of the general-purpose knobs. The other knob then lets you change the intensity of the traces on the screen. Fig.2: this shot shows the Wave Inspector feature applied to a sinewave. You can see that the display has been split and the top window shows you the entire recorded wave train. The bigger, bottom window then shows the zoomed-in part bracketed out in the top window. In each case, you can pan across the record and zoom in on it using two concentric knobs. The pan knob has a jogging action. Fig.3: this is not just a DSO (Digital Storage Oscilloscope), it’s actually an MSO (a Mixed Signal Oscilloscope) as this screen demonstrates. In this shot, eight digital channels are recording the activity on the driving pins of a static LCD display. The square driving signals on the segments can be seen (some are in phase and some are out of phase with the backplane drive). You can select three different sizes for the digital traces and even move them around. Fig.4: a sinewave (green trace) at around 4.5kHz is shown while above it is the result of the MATHs function (red trace) which shows the square of the sinewave. The MATHs trace is computed in real time but we found the response of the oscilloscope was sluggish with the record length set to 1Mpts. We therefore changed it to 125kpts to speed up the response, especially of the MATHs trace rendering. You can also perform the FFT using the MATHs features. Apart from that, you can vary the persistence of the dots for periods ranging from 400ms up to around 10 seconds and then to infinite persistence. This would be useful to see fine or quickly changing details of the waveform. User interface The oscilloscope has dedicated vertical sensitivity and offset knobs for each of the four analog channels. This makes it considerably easier to use than if the controls were “doubled” up. Below the sensitivity knobs are the four associated BNC sockets which are probe sensing as well as being able to work with active probes. However, the four 10:1 probes supplied with the scope do not have the plugs to enable auto sensing. To explain further, with probe-sensing inputs, the scope automatically changes the vertical sensitivity displayed on the screen. So if you select a sensitivity of 1V/div and then plug in a 10:1 probe, the displayed sensitivity will take the probe attenuation into account and change to 10V/div. There is an extra BNC connector for the auxiliary trigger input and a rectangular connector for the 16 digital siliconchip.com.au channels. Around the screen itself is an array of “soft buttons” whose function changes according to the displayed menus. These are easy to use because their functions are indicated next to or above them on the screen, according to which menu you are in. A screen grab of a typical menu is shown in Fig.1. There are two general-purpose knobs with digital clicking action referred to as “a” and “b”. According to which menu you are in, you use these to vary settings. Again, their function is clearly indicated on the display. The other knobs relate to (1) the trigger level (pushing this knob sets the trigger to 50%), (2) the timebase and (3) the pan and zoom controls. The latter are two concentric knobs. The larger of the two has a jogging action, allowing you to pan the waveform, while the smaller one allows you to zoom in on the waveform by as much as 10,000 times! Replay & review waveforms The pan and zoom features are part of the so-called “Wave Inspector” module. A small window appears in the April 2009  77 of “FilterVu”. This allows you to capture glitches in your signal while still filtering out unwanted noise. The way it works is that two waveforms are displayed superimposed. One is a filtered waveform (with reduced noise components) while the other captures any glitches. This is similar to the “peak-detect” feature in some other oscilloscopes and can help in seeing fast glitches in a signal that may be the difference between reliable operation of a circuit and intermittent failures. Trigger options Fig.5: the list of possible measurements is extensive. One of the nicer features is that you can take a snapshot of all the measurements at the touch of a button. This shot shows the result of applying the snapshot to a sinewave and we can see that the frequency is around 4.5kHz, the DC offset is around -175mV and the RMS amplitude is close to 2V. Remember that some of these measurements are “equivalent”; for example, frequency is the reciprocal of period. Fig.6: a screen grab of the OpenChoice PC software. This shows a screen grab on the PC, as captured from the oscilloscope. The PC is connected to the oscilloscope via a USB cable, using the USB device port on the back of the MSO2024. top of the screen showing the entire captured wavetrain. You can then use the pan control knob to move forwards or backwards in time from the trigger point. But you can do even more than that. You can mark points in the record and move between them at the touch of a button, and even search the record. The criterion for a search match is similar to the trigger options. You can, for example, search for a rising edge, a particular positive pulse width and so on. The difference is that it is applied to the captured wavetrain rather than the real-time signal. There is one further advantage: once the wave train has been captured, you can experiment with different searches! You may then mark the relevant points where the search found the trigger and go back to it or scroll back and forth between saved markers. A screen grab showing the Wave Inspector is shown in Fig.2. Capturing fast glitches This oscilloscope has another feature by the odd name 78  Silicon Chip Triggering is an integral part of the operation of any oscilloscope, as in normal acquisition mode, the oscilloscope will only display a waveform once the trigger condition is met. Choosing the appropriate trigger can mean the difference between capturing detail relevant to you or not. So how does the MSO2024 measure up in terms of triggering options? As commonly found in current oscilloscopes, the trigger can be AC or DC-coupled or low or high-pass filtered to reduce spurious noise. You can select a hold-off period from the last trigger point during which the triggering is effectively disarmed. The hold-off prevents spurious triggering due to level transitions and other artefacts in the signal. The standard triggering modes of the MSO2024 include the usual edge and pulse-width triggering modes as well as standard video triggering (NTSC, PAL, SECAM). Runt triggering allows you trigger when a signal rises above a preset threshold voltage but fails to clear the voltage threshold subsequently. For edge triggering, you can select a rising or falling level and select the threshold voltage. For pulse width triggering, you can choose the polarity of the pulse (positive or negative), its minimum amplitude and width. Since this is a mixed-signal oscilloscope, you can also trigger on the logic conditions from one or more of the 16 digital channels. For example, you can choose to trigger when one digital input is high while another is low. Digital inputs We should mention that the 16 digital channels are synchronised to the analog waveforms. You can also select the voltage threshold for the digital channels. For example, you can define a high level to be anything above 2.5V and a low level to be below that. The digital threshold voltage can be set arbitrarily or chosen from a list of known logic families like TTL or 3.3V CMOS. The MSO2024 comes with an adaptor that plugs into the front of the oscilloscope to connect the 16 digital inputs and they can easily be attached to the leads of most ICs. The screen grab of Fig.3 shows some digital waveforms on the screen. Optional modules You can purchase additional modules to enhance the features of the oscilloscope. For example, there are modules to decode serial protocols like I2C, RS232/485, LIN, CAN and SPI, as well as HD TV formats. The serial protocols will be especially useful for debugging embedded systems, as these typically use a number of serial protocols. The MSO2024 also includes, for the serial protocols, an event table. This is a log of the relevant decoded data in siliconchip.com.au Specifications At A Glance Analog channels: Digital channels: Analog Bandwidth: Sampling Rate: Memory Depth: Vertical Sensitivity: Vertical Resolution: LCD display: Net Weight: 4 16 DC to 200MHz 1GS/s 1Mpts 2mV/div – 5V/div (x1 probe) 8 bits 7-inch widescreen QVGA LCD (480 x 234 pixels) 4.08kg chronological order. The optional modules come as small “cards” that plug into ports on the front panel. Note that for the modules not installed in your oscilloscope, there is a 30-day free trial, activated when you first use it. Making measurements All the usual measurements you would expect can be made, like RMS, frequency and peak-to-peak voltage. In fact, the range of measurements is quite comprehensive, including rise and fall times, burst width, cycle RMS and mean, overshoot, etc. One nice feature is that you can take a “snapshot” of the waveform in which case all measurements are applied to it. This gives you a very easy way of taking the vital statistics of a waveform and is shown in Fig.5. MATHs features The MATHs features of this oscilloscope allow you to add, subtract and multiply two waveforms and display the result as a separate (red) trace. You can also perform the FFT (Fast Fourier Transform) on an input channel, which effectively separates the signal into its frequency components. In Fig.4 we show the result of using the MATHs function to compute, in real time, the square of a sinewave. Maths waveforms can be created from real-time channel data or from previously stored reference waveforms: there are two of these and they are stored in non-volatile memory. The oscilloscope’s response is slow at times. We found it especially slow when displaying the MATH trace with the full 1Mpts record length but this improved once we lowered the record length to 125kpts. By the way, updating the firmware is quite easy. You simply download the file from the Tektronix website, copy it to a USB flash drive and insert the drive into the oscilloscope’s host USB port on the front panel. The oscilloscope then recognises the files and starts the update process. USB ports & software The MSO2024 has a USB host port on the front panel for connecting a USB flash drive. You can then use the supplied software to save screen grabs and oscilloscope settings (you may subsequently restore the settings). There is also a USB device port on the back of the oscilloscope. This allows you to connect it to a PC and by using the supplied data logging software, NI LabView’s SignalExpress, you can remotely control the oscilloscope and acquire screen grabs directly. Remember that the LAN port is not standard, though. Available options are Ethernet and GPIB ports, as well as a module that plugs in at the back of the oscilloscope and provides VGA and LAN connections. Conclusion The MSO2024 is an affordable scope with many features found in more expensive models. In particular, the measurement options are comprehensive, the Wave Inspector that allows you to pan and zoom the stored waveform is the same as used on higher end models. The firmware is among the best we have seen. The menus are intuitive to use and the logic of the interface is easy to learn. The ability to make automatic and custom measurements and to search, zoom in on and play back waveforms makes this oscilloscope a desirable debugging tool. The MSO2024 is supplied with four 200MHz passive probes, a 16-channel digital adaptor, manuals NI LabView SignalExpress and Open Choice PC software and a 3-year warranty.The price is $A9760.00 (ex. GST). The VGA and LAN interface is priced at $A749.00 (ex. GST). It can be purchased from Tekmark Australia, Suite 302, 18 Orion Rd, Lane Cove, NSW 2066. Phone: (02) 9911 3888 or visit: SC www.tekmark.net.au The MSO2024 is supplied with four 200MHz passive probes and a 16-channel digital adaptor. siliconchip.com.au April 2009  79