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A high performance colour scope in a shoebox Here’s a machine that many engineers and technicians would kill for: a four channel 100MHz scope with a VGA colour liquid crystal display, inbuilt disk drive, parallel printer port and a host of measurement facilities and it all fits into a case the size of a shoebox! Review by LEO SIMPSON Tektronix TDS 3014 four channel colour oscilloscope July 2001  81 F or a number of years now we have been using a Tektronix TDS 360 1GS/s 200MHz digital scope for most of our measurements. You would have seen the scope traces published regularly in the pages of SILICON CHIP. We have really liked that scope for its combination of performance and features and at the time of purchase, we considered it the best overall value for our application. Tektronix have moved on quite a way since producing the TDS 320/340/360 series and their low-end scopes are now compact instruments featuring liquid crystal displays. In view of this, we decided to have a look at what is perhaps their benchmark instrument in the TDS 3000 colour range, the model TDS 3014. This is a four-channel scope with a 100MHz bandwidth and a maximum sampling rate of 1.25 Gigasamples/second. Our review sample was also fitted with the TDS 3TRG advanced trigger module and the TDS 3FFT (Fast Fourier Transform) module to give measurements in the frequency domain (ie, spectrum analysis). So all up, this is a high performance combination in a pretty compact package. In fact, if you are familiar with the typical digital oscilloscope of just a few years ago, you will know that they are fairly bulky instruments. For example, the TDS 360 model referred to above has an overall depth of about 470mm, not including the handle. By contrast, the model TDS 3014 has roughly the same width and height (just a little more) but its depth is only 145mm. In other words, it is about the size of a shoebox (albeit a pretty expensive one!) In regard to weight, the model TDS 360 tips the scales at about 7kg while the TDS 3014 is half that, at about 3.5kg, making it highly portable. So not only is the new model half the weight, it takes up only a fraction of the bench space required for the old model. In most applications, that is a very important advantage. Digital phosphor oscilloscope As far as Tektronix is concerned, the big feature of the TDS 3000 series is the colour VGA liquid crystal display and you have to agree that compared to the conventional green monochrome CRT, the colour screen is a big advance, particularly when you have up to four (or more) traces on screen. Each trace has a different colour and with the addition of the Math function trace, you can have up to five different coloured traces on screen: Channel 1, yellow; Channel 2, cyan (blue); Channel 3, magenta (pinky/purple); Channel 4, green; and Math, red. In addition you can also display up to four REF waveforms and these are all shown in monochrome (ie, white). To see how busy the screen can be with the maximum number of traces displayed, have a look at Fig.1. Trying to examine a mono screen with all those signals would be impossible. Mind you, you can select monochrome for all traces instead of colour but why anyone would want to do that escapes us. Maybe if you are colour blind? Some readers may be wondering why Tektronix refer to this range of scopes as DPOs which stands for “Digital Phosphor Oscilloscope”. This refers to the Tektronix method of intensity modulation which imitates the screen phosphor of an analog CRT (cathode ray tube) oscilloscope. Areas where the signal is concentrated (as in an amplitude-modulated 82  Silicon Chip Fig.1: This shows the capability of the VGA (640 x 480 pixels) display to show a lot of waveforms on the screen. In this case we have the four channels, a MATH waveform (in red) and four REF waveforms (in white). Fig.2: For easy setup of scope parameters, go to the QuickMenu. This displays and allows you set Vertical, Acquire, Cursors and Trigger parameters. Fig.3: This is another subset of the QuickMenu options, showing the Video triggering options. (Yes, we know those aren’t video signals). Fig.4: This screen has four measurements selected, for different channels. If you try to select more measurements, the scope will throw up a message on the screen telling you to remove a measurement before you can select another. RF signal) appear the brightest and areas where the signal is moving fastest (ie, rising and falling edges of pulses) appear dimmer. While we don’t particularly like the Tektronix DPO label for this technology, it is a big advance on previous digital scopes and gives a more realistic (ie, analog) picture of the signal you are measuring. Having said that, you can vary the degree of intensity modulation on the waveforms by using the “Waveform Intensity” knob on the righthand side of the control panel. Also, the REF and Math waveforms are constant brightness; ie, no intensity modulation is used. You should be able to see this effect in Fig.1. Before we leave the subject of the colour screen, we thought that it would have been nice if the probes had matching colour rings to identify them. On our review machine, they were supplied with red, white, orange and black rings. Why not make them available in the four colours displayed on the screen traces? This would also match the channel selector buttons on the control panel. I contacted Tektronix and suggested it. Guess what: current production models have the probe rings matching the channel colours. Ease of use Fig.5: Once you clear the measurement menu off the screen (by pushing the Menu Off button) the four measurements are then displayed to the right of the screen and do not clutter the waveforms. Fig.6: Normal MATH functions in the TDS 3000 series allow you to add, subtract, multiply or divide any two channel signals together, or any combination of the input channels with any of four stored reference signals. This screen shows the MATHematics trace in red, as the sum of channels 1 and 3. Two things we particularly liked about the TDS 360 were the ease of use, in getting a waveform on the screen and then varying all the display parameters, and then selecting a whole range of measurements of which four can be displayed on the screen at any time. The TDS 3000 series is even better in this respect, particularly in respect to its “QuickMenu” button. As before, you can connect any or all of the four channels to signals and press the “Autoset” button to set the timebase and vertical sensitivity on each channel to display a useable trace. At the same time, the scope triggering selects the lowest active channel as the source, usually Channel 1. From there you can go in and change the vertical, horizontal (timebase) and trigger settings and a bunch of other features to get the scope display you want. But doing all of that would normally require quite a few button presses. On the TDS 3000 series, you can bypass a lot of those steps by pressing the QuickMenu button; it displays a whole lot of scope settings, as shown in Fig.2. Note that the vertical sensitivity for all active channels is always shown at the bottom of the screen and again, the colours match the traces. Also shown are the timebase setting, the channel selected for triggering (Channel 1, in this case), the trigger slope, trigger level and trigger time reference. QuickMenu information is displayed below and to the right of the screen graticule. At the bottom are the vertical input conditions for the selected channel (Channel 3, in this case), the Acquire settings and Cursors (Off, Vertical or Horizontal). Trigger settings are shown to the right of the screen, in five separate boxes: Trigger type (edge or video), Trigger mode, Trigger source (channel 1, 2, 3 or 4, Alternate or AC line), Trigger Coupling (DC, Noise reject, HF reject or LF reject) and Trigger slope. Note that each one of the displayed QuickMenu settings can be changed by pushing the adjacent button (below or to the right of the screen; you do not have to go back to the individual menus to make these changes. July 2001  83 Note also that if you select Video triggering from the QuickMenu display, it all changes, as shown in Fig.3. You then have the choice of Video standard (NTSC, PAL or SECAM) and field or line triggering (Even, Odd or All fields or All lines). Yes, we know that Fig.3 doesn’t show video waveforms but we got lazy for this screen grab. By the way, the waveforms shown in Figs.1, 2 and 3 are from the Li’l Pulser switchmode train controller published in the February 2001 issue of SILICON CHIP. I should note that on our review sample, if you press the Trigger menu button, you have more options apart from Edge and Video triggering: Logic and Pulse triggering and all the associated parameters. These are the additional features of the Advanced Triggering Module. For example, if you go for pulse triggering, you can select width, runt and slew rate, with the latter set to ECL, TTL or adjustable high and low thresholds. That’s pretty comprehensive. Measurements Where the Tektronix TDS 3000 series really shine is in the Measurement department. Not only is there a host of different measurements but they do not interfere with the waveform display. Some other scopes we have seen throw up cursors whenever you select an amplitude or frequency-related measurement and those cursors ride on the waveform while ever the measurement is displayed annoying. In all, 21 different measurements are available, including Frequency, Period, Rise & Fall Time, Positive & Negative Duty Cycle, Positive & Negative Overshoot, Peak-Peak, Amplitude, Mean, RMS and so on. Only four measurements can be displayed at a time and they can all relate to one selected channel or to all four channels (but still only four measurements can be displayed). As you select each measurement for a designated channel it is displayed on the righthand side of the screen. Fig.4 shows a screen with four measurements selected, for different channels. If you try to select more measurements, the scope will throw up a message on the screen telling you to remove a measurement before you can select another. A good feature is that once you clear the measurement menu off the screen (by pushing the Menu Off button) the four measurements are then displayed to the right of the screen and do not clutter the waveforms. Fig.5 shows the result. This is particularly important if you want to save the screen waveforms to a monochrome printer – you do not want measurements printing over waveforms. Again, notice that the displayed measurements are in the same colours as the designated channel. This is just one of the little niceties that you get with a colour display. We mentioned printing the waveforms and the TDS 3000 series come standard with a parallel printer port and a whole bunch of inbuilt generic printer drivers. Normally though, connecting a printer is too much of a hassle and most users would probably prefer to save the printer files to the floppy disk drive for printing later on. Of course, we take the scope files and include them in our published articles. But just how do you go through the process? Well, it ain’t intuitive, that’s for sure! And it is not at all obvious even after reading the relevant sections of the manual, under the heading “Save/Recall”. We did manage to do it, as is evidenced by the waveforms in this article. What you don’t do is to push the Save/Recall 84  Silicon Chip Fig.7: This screen shows the FFT trace (red) when channel ? is selected for analysis. You can set the vertical scale to linear or dbV RMS and the FFT window to Hamming, Blackman-Harris, Hanning or Rectangular. Fig.8: This NTSC video waveform is a good illustration of the intensity modulation of the VGA display. This is every bit as good as the equivalent screen on an analog scope with a conventional CRT. Fig.9: This is the same video signal as in Fig.8 but with triggering on all lines of the signal. Maths functions Fig.10: Winding the timebase up to 1µs/div lets you view the colour burst of the video signal in Fig.9. button. This will certainly read the directory of any disk that happens to be in the drive but you will go red in the face trying to save screen grabs to it. You can save and recall waveforms, either to internal memory or the disk but that is entirely another matter. No, what you have to do is press the Utility button and then cycle through the screen menus to bring up Hard Copy. You then press Port Centronics and change it to Port File (Aaah!). But that’s not the end of the story. You then have to choose the Hard Copy format and you have 16 options, ranging from mono and colour inkjet printers, laser or dot matrix printers and files in formats such as TIFF, EPS, BMP, PCX, IMG and so on. And you can also choose Landscape or Portrait orientation for your printouts. OK, so we chose TIFF format. What to do then? It had us really tricked. Finally, the light went on and I pressed the Printer button on the lefthand side of the screen and the disk drive started whirring merrily away. As Homer Simpson often exclaims, “Doh!”. I suppose it should have been obvious but it wasn’t. Of course, as with the previous model TDS 360, once you set these things up, you seldom have any reason to change them and it can be really hard to figure out how you did it. And finally, as an embarrassing footnote to my detective work, I then found the disk save procedure a couple of nights later, clearly outlined on page 3-21 of the instruction manual, under the heading “Hard Copy”. Yes, I know, I know: read the instruction manual! Normal MATH functions in the TDS 3000 series allow you to add, subtract, multiply or divide any two channel signals together, or any combination of the input channels with any of four stored reference signals. Fig.6 shows the MATHematics trace in red, as the sum of channels 1 and 3. Our sample machine also had the FFT module fitted so you can do an FFT (Fast Fourier Transform) analysis on any of the four channels or any of the stored REF signals. Typically, the bandwidth of the FFT is limited by the timebase setting. The same comment applies to the sampling rate. The maximum sampling rate is only available for timebase speeds of 1µs/div and above. Fig.7 shows the FFT trace (red) when channel 1 is selected for analysis. You can set the vertical scale to linear or dbV RMS and the FFT window to Hamming, Blackman-Harris, Hanning or Rectangular. Video waveforms Finally, a demonstration of the TDS 3014’s performance on video waveforms. Fig.8 shows an NTSC video waveform and is a good illustration of the intensity modulation of the VGA display. Fig.9 shows its performance when triggering on all lines of the signal. The triggering is effective enough to easily examine the waveform but not quite stable enough to allow reliable measurements such as frequency. To do that, you would need the line triggering feature in the optional video triggering module. Fig.10 shows the timebase wound up to 1µs/div to display the colour burst. Summary As with any review of a complex digital oscilloscope it is just not possible to do full justice to all its features in a few pages. However, having used it for a few weeks, we can see why it is one of the best selling Tektronix scopes ever. Its combination of compact size, light weight, colour display and 100MHz 4-channel performance plus exellent measurement facilities make it a very attractive package to any engineer or technician. For further information on the TDS 3000 series you can check the website at www.tektronix.com or phone (02) 9888 0100. Pricing on the review TDS 3014, complete with four passive 10:1 probes, the advanced trigger and FFT modules SC is $9882 including GST. At the rear of the TDS 3014 is the standard parallel port and a compartment for the optional battery pack. When this option is not used, the compartment is handy for storing a couple of probes. July 2001  85