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TekTronix DPO3034 Digital Phosphor Oscilloscope Review by Mauro Grassi The 300MHz DPO3034, with its wide “digital phosphor” LCD screen, is a serious oscilloscope with an impressive list of features and an excellent user interface. T he TekTronix DPO3034 is an impressive oscilloscope with the latest version of Tek’s “digital phosphor” screen and advanced features like extended MATHs functions and waveform replay, zoom and search. Its bandwidth is 300MHz and the sampling rate is 2.5Gs/s for each individual channel. With some 4-channel oscilloscopes, the sampling rate is shared among the channels or pair of channels. This means that the effective sampling rate is frequently half that of the quoted specification, when all channels are in use. However, this oscilloscope achieves 2.5GS/s on each channel at all times. The vertical resolution of the digitising system is 8 bits and the sensitivity is better than most comparable oscilloscopes, ranging from 1mV/div to 10V/div. Phosphor display This scope has the latest version of Tek’s so-called “digital phosphor” display. The colour screen is a 228mm (9-inch) (diagonal) WVGA (wide VGA: 18  Silicon Chip Specifications at a glance: Input channels:..... ... 4 Analog Bandwidth: .... DC to 300MHz Sampling Rate:..... ... 2.5GS/s at all tim es for each channe Memory Depth:..... l ... 5Mpts Vertical Sensitivit y:... 1mV/div to 10 V/div Vertical Resolutio n:.. 8 bits LCD Screen:........ ... WVGA (800x480 pixels) Screen size:........ .... 22.8mm (9-inch ) diag Weight:.............. ... 4.2kg 800 x 480 pixels) LCD that looks bright and shows good contrast. The display refresh rate is fast at 50kHz. The screen emulates the desirable features of the phosphors used in analog oscilloscopes employing CRTs (Cathode Ray Tubes). The intensity of the traces can be varied over a wide range while the persistence time can be selected from periods ranging from 10 seconds down to milliseconds. This is useful when you have fast glitches or you are using single step triggering. Interestingly, the display has a wide screen aspect ratio and is 198mm wide by 120mm high (1.65:1). This allows you to see more time domain data and effectively gives you the advantage of an even larger screen. Replay and review waveforms One of the best features of this oscilloscope is its ability to capture and replay waveforms. This feature is part of the so-called Wave Inspector module. It has a zoom and pan control knob that allows you to search and mark the waveform data by comparing it to a preset trigger pattern. Its deep memory of 5Mpts (million points) means that at a reasonable resolution acquisition rate of say 100Kpts you can capture almost a minute of waveform data. Wave Inspector then allows you to mark and search waveforms. You may be interested in a small portion of a waveform, one that may occur relatively infrequently yet occurs very quickly. While having a deep memory is essential, it is also essential to be able to search that large memory. The search feature functions much like a trigger except that it is applied to an already acquired waveform rather than a real time waveform. There is the added advantage that once the data has been captured you can try 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.1. You can also pan and zoom in on parts of the captured waveform to insiliconchip.com.au spect it in closer detail. These features make the DPO3034 a very powerful debugging tool. Advanced triggering As is usual in current oscilloscopes, the trigger can be AC or DC-coupled or low or high pass filtered to reduce spurious noise. The standard triggering modes of the DPO3034 include the usual edge and pulse triggering modes as well as standard video triggering (NTSC, PAL, SECAM). For the newer HD (high definition) TV formats however, the DPO3034 must be upgraded with an optional module. The DPO3034 also has some advanced triggering modes, one of which is sequential triggering. This mode allows you to select a primary trigger and a secondary trigger. The triggering will occur only if the primary trigger occurs followed by the secondary trigger. Normally the two triggers would take their input from different channels. Optional modules Application modules are available to enhance the DPO3034. These are siliconchip.com.au unlocked by purchasing an additional licence. For example, there are modules to decode serial protocols like I2C, RS232/485, LIN, CAN and SPI as well as for the HD TV formats, as mentioned previously. The serial protocol modules are especially useful if you are debugging an embedded application. It is common to find a few different serial busses operating concurrently even if all you are using is a small microcontroller. In Fig.2 we show the result of decoding an RS232 stream using the optional module. The DPO3034 also includes, for the serial protocols, an event table, shown in Fig.3. This is a log of the relevant decoded data in chronological order. These modules are implemented as small “cards” that plug into one of four ports on the front of the oscilloscope. The automotive serial protocols CAN/LIN are separate to the data protocols, so you will need two different modules if you want all of these. Considering that many cars use both CAN and I2C this could have been better offered as a single module, especially since the number of upgrade ports is limited to four. Unfortunately, you cannot trigger on these serial events or on the optional video formats unless the module is installed. Some oscilloscopes allow you to trigger on serial protocols and only the decoding is optional. For the DPO3034 you need the module for both triggering and decoding. For modules not installed in your oscilloscope, there is a 30-day free trial activated when you first use your oscilloscope. Probes The DPO3034 and other oscilloscopes in this range are supplied with one 500MHz passive probe per channel. Each of the four BNC inputs has auto-sensing and can also provide power for active probes. In fact, the DPO3034 can provide up to 20W of power for active probes. August 2008  19 Fig.1: this shows the Wave Inspector enabled. Having captured an audio stream, we can zoom in and “play” it back. The small white triangles visible at the top of the bottom window indicate the edge trigger events (the triggering was set to a falling edge at 0.0V and the audio stream is AC coupled). You can then pan across from one marked event (trigger) to the next inspecting the captured waveform data. Apart from the usual passive probes, you can optionally use current sensing and differential probes. The input impedance of each channel can be selected from 1MW, 75W or 50W. The 50W input impedance is useful for RF circuit analysis, while 75W is used for TV or video work. The DPO3034 incorporates in-built 75W terminators that will be appreciated by video technicians, as this is not commonly found in oscilloscopes. Each channel can be AC or DC coupled and bandwidth limited to 150MHz or 20MHz. In general you should use the lowest bandwidth which will still give optimum resolu- tion. Any higher bandwidth will just add noise to the signal. MATHs features The MATHs features of this oscilloscope are exceptionally good. You can do real-time FFT analysis on a signal but you can also define a general mathematical expression and display it as a trace on the screen in real time. In Fig.4 we show the result of using the MATHs function to compute, in real time, the gain-bandwidth product of an op amp. Maths waveforms can be created from real time channel data or from previously stored reference wave- Fig.5: a Triac controlling a mains light using phase control. We have used a 100:1 probe to monitor the A1 output of the Triac (green trace) and the vertical scale stands at 200V/div. The cycle RMS measurement for this channel shows 218V and the duty stands at 72%. Also shown is the gate pulse used to turn on the Triac through an optocoupler (pink trace). The positive pulse width of the gate turn on is measured to be 140.4us. 20  Silicon Chip Fig.2: a decoded RS232 stream from a microcontroller as the B1 trace (purple). The data format is set to 8 bits, no parity and one stop bit, while the baud rate is set at 9.6Kbps. The decoded data is shown as a hexadecimal byte (0xE2) and the triggering occurs on the start bit. Custom baud rates are also allowed for non-standard systems. The input to the decoder is shown as the yellow trace, which is channel 1. forms. You can also inspect the maths waveforms like any other waveform. You can use a maths waveform to estimate the power consumption of a circuit or integrate a waveform to estimate the brightness of a light source driven in switchmode. Fig.5 shows the result of measuring the output of a Triac in switchmode. Making measurements All the usual measurements of a waveform can be made: RMS, frequency and peak-to-peak voltage etc. You can also capture a “snapshot” of a waveform. In this case, all measurements will be taken simultaneously. Fig.6: the OpenChoice PC software supplied free-of-charge with the oscilloscopes in this series. It allows you to record your work with the oscilloscope and store important settings. Interface with the oscilloscope is via the USB port (connecting cable supplied). Other software is also supplied. siliconchip.com.au Fig.3: the event table associated with the serial stream shown in Fig.2. The single byte of data is shown in the table and the time relative to the trigger point (155.6us) chronicles the activity on the channel. The event table can be exported to a computer for storage or further analysis either by saving to the on board non-volatile memory and transferring later to a PC or by saving to a USB flash disk connected to the host port on the front. You can also customise an automatic measurement. For example, gating is the name given to restricting measurements on a waveform to a specific portion. With gating enabled, you can restrict the chosen measurement to within the visible screen area or to within the area designated by cursors. Measurement indicators can be turned on and switched off. This allows you to see on the display the actual part of the waveform that the displayed measurement corresponds to. It can be considered a kind of automatically set cursor. Cursors can also be used for manual measurements on stored or real time waveforms, including the output of the MATHs function. Connections & software The DPO3034 has all the connections you would expect as standard: a built in ethernet port, USB 2.0 device and host ports and video output for connecting an external monitor. A variety of PC software is supplied with the scope. OpenChoice software shown in Fig.6 allows you to save screen grabs and settings. The settings can then be recalled at a later time. There is also data logging software supplied, NI LabView SignalExpress which allows you to remotely control the oscilloscope using an ethernet, USB or GPIB port. You can, for example, obtain a live waveform display from the oscilloscope through your network, and by extension, through a siliconchip.com.au Fig.4: the MATHs function (red trace at top of screen) used to compute the gain-bandwidth product of an amplifier. The input is a sinewave at around 3kHz and 1.5V RMS (yellow trace). The gain is computed by dividing the amplitude of the output (cyan trace) by the input. We then multiply this by the real time measurement of the input frequency. The measured mean of the result is around 38,900. range of inter-networks. NI LabView SignalExpress software can also produce statistical reports including histograms and can be used for limit testing. Limit testing refers to the procedure for measuring the limit-cases (ie, the maximum and minimum levels) and is useful for rating a design and ascertaining the best and worst cases for operation. For example, what’s the absolute maximum current drawn and power dissipated by a circuit? Conclusion The DPO3034 is a serious oscilloscope with an impressive list of features and an excellent user interface. We have very few negative things to say about this oscilloscope. The user interface sometimes is slow to respond to changes in settings. However, this only occurs at certain points in the menus and does not affect the waveform display when running. The Auto Set feature can take up to five seconds which is slow compared to other oscilloscopes. However, it is still much shorter than if you had to change all the relevant settings manually. On the other hand, the user interface of the DPO3034 and what you can do with it is among the best we have seen in comparably priced oscilloscopes. The general MATHs features are powerful. 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. It has an attractive screen and many connection options as standard. The DPO3034 is supplied with four 500MHz passive probes, manuals and NI LabView SignalExpress and Open Choice PC software. The price of this particular model is $9832.00 (ex GST). Other oscilloscopes in this Tektronix range are priced from $5680 (2 channels, 100MHz) to $13960.00 (4 channels, 500MHz). The optional modules are priced at $1265.00 (I2C/SPI decoding and triggering), $1265.00 (CAN/LIN decoding and triggering), $1265.00 (RS232C/ RS422/485 decoding and triggering) and $799.00 (HD TV decoding and triggering). It can be purchased from Tekmark Australia, Suite 302, 18 Orion Rd Lane Cove, NSW 2066. Phone: (02) 9911 3888 or visit www.tekmark.net.au SC A NOTE TO SILICON CHIP SUBSCRIBERS Your magazine address sheet shows when your current subscription expires. Check it out to see how many you still have. If your magazine has not turned up by the first week of the month, contact us at silchip<at>siliconchip.com.au August 2008  21