标签: Generator

My dad grew up during the depression and was in the Navy in the tail end of WWII. He had little use for Japanese products, and to this day sniffs at anything from China. If it’s not made in America he’s not interested in the product, and anything from China is, in his opinion, junk.   Thankfully he doesn’t read these columns, because Siglent sent me their very new SDG2042X arbitrary waveform generator (AWG), which is made in China, and, well, American competitors may find themselves squeezed by the product. It’s in a hefty metal box with a plastic handle and shock protectors and feels as solid as anything from the big guys. If “Siglent” were erased from the label I’d assume it was from Keysight or Tektronix. The difference is that the Siglent costs $500 and the others are (at least) ten times the price. I have one of Siglent’s lowest-end scopes and, while I like it, it’s noticeably more “plasticy” than my Agilent (though much less costly). The AWG hasn’t a bit of cheap or plastic feel to it.   Sexy looking thing, isn’t it? The unit has two independent and duplicate channels. So you’re getting two AWGs in one.   A hugely-important specification for any AWG is the sampling rate. Generally there’s no one number for a particular unit, which is the case with the SDG2042X. For the basic built-in waveforms memory is sampled at 300 MS/s. However, and possibly uniquely to this unit, another clock interpolates the data four times for each sample period. The result is an effective rate of 1.2 GS/s. Now, that’s on the built-in signals like sine, square, etc. For arbitrary waveforms the unit samples at 75 MS/s.   Vertical resolution is 16 bits, on a par with the best units available, with a 20 Vpp output. The unit they sent me is 40 MHz (sine waves; other waveforms are slower). An 8 million point buffer means it will generate just about any sort of signal. It includes all of the usual modulations like AM, DSB-AM, FM, PM, FSK, ASK and PWM. Each of those are controllable; for instance, the shape of the modulating signal is selectable. Normally one might sine-wave modulate an AM signal, but the unit can use any of a number of shapes, or even an arbitrary shape. I used the EasyWave software (more on that later) and created totally random waveforms which were stored in the AWG’s memory. Those can be recalled and used, not only to generate a signal, but as the shape of the modulating signal.   This is a sine wave modulated by an arbitrary waveform created on my PC. It will generate swept signals; one enters the start and stop frequency (or, center and span for RF folks who think in terms of spectrum analyzers), as well as the sweep rate. You can get some pretty cool-looking signals when sweeping through many MHz in a ms. Burst operation is supported as well.   Pulse rise and fall times are completely variable, with rise times down to 8.4 ns. Frequency precision is rated at ±1 ppm. At 40 MHz I measured a 0.5 ppm error. A frequency counter (the signal goes to a rear-panel BNC connector) is available that works even when both AWG outputs are operating. With a resolution of 1 Hz it was spot-on to the signal I provided.   The two channels can be linked in a variety of ways. One can have a frequency, amplitude or phase that is some multiple (integer or otherwise) of the other, or that can have some offset from the other. So channel 2’s frequency can be twice that of channel 1’s, or it could be 1.22345 Hz higher. In the following picture the scope shows the output of the two channels when one’s frequency is twice the other. If I had taken a single sweep instead of running continuously, the Lissajous curve on the top trace would be a simple sine wave with half the frequency of the blue trace. But this looks cooler:     The unit has a touch screen which works well, but I found it more convenient to use the buttons. The screen is bright and the letters very crisp. It does show a graphical view of the signal being produced. This is quite accurate even for arbitrary waveforms created using the included PC software. The one case I found where the display doesn’t mirror the output is for pulses when you’re adjusting the rise time. There’s so much control of that parameter it’s easy to turn a pulse into a ramp, but the screen always shows a pulse.   An AWG is conceptually pretty simple: just scan through memory tossing data to a DAC. The devil is in the details, including the analog. One quality metric is a sine wave’s harmonics. In the unit supplied to me these were an amazing 70 dB down from the 40 MHz fundamental. That’s 15 dB better than the spec and about equal to Keysight’s $5000 33612A.   The included “EasyWave” PC-hosted software can control the AWG. Documentation is scarce and I couldn’t figure out some of the functionality. There is a help file, but it was complete gibberish, most likely being a binary file of some sort. Fortunately, most of the features are pretty easy to figure out. One nit: to send a waveform to the unit one presses “Send Wave”, but then one must, every time, select USB or Ethernet, and then a device selection menu appears. What should take one click requires three.   The software has a lot of capability. A number of waveforms are built-in, and of course it will import a .csv file. It’s trivial to hand-draw a signal and download that to the AWG. Intriguingly, one can enter equations to create a signal; supported functions and operators are sin(), cos(), abs(), sqrt(), e, log(), pi, +, -, *, and /. The unit faithfully produces the desired signal, and that is shown on its display. The following is a screenshot of the EasyWave software displaying the signal 2*sin(x)+cos(x*pi):     What’s the worst thing I found about the unit? The big control wheel that selects parameters like frequency works well, with one glaring exception. Suppose the frequency is 25.100 MHz. If the “5” is selected, rotating the knob to the left decreases it exactly like you’d expect. Until it hits “0,” at which point the cursor jumps to the digit to the right of the decimal point. So while cranking numbers down you suddenly find yourself selecting the fractional part when most of the time you want to continue setting the integer part.   The SDG2042X does everything one would expect from a high-end AWG at a price that can’t be beaten. With 16 bits of vertical resolution, an 8 mega-point buffer, fast sampling, and a very complete set of features it’s a professional unit that will more than satisfy all but the most demanding engineer. I reviewed the 40 MHz model, but 80 and 120 MHz variants are available for $619 and $899 respectively. There’s more info here .   But don’t tell my Dad I like this Chinese product.

eBay is a treasure chest of test equipment. It’s astonishing the deals one can get on used equipment. Need an oscilloscope? If you can live with yesterday’s technology there are lots of excellent Tek, Agilent and HP versions there for surprisingly low prices.   Vendors offer plenty of brand-new gear on that site as well. Some Chinese vendors sell indigenous gear. How good is this stuff? I bought a no-name signal generator, which is labeled “SSD Signal Generator/Counter” from the site for $50. It was shipped directly from China and arrived in about 10 days.     You can see it has no enclosure, but does sport a small display with pretty decent controls. In fact, the push buttons have a very crisp action. The knobs, too, feel professional. The topmost has detents, and probably is an encoder. The other two are clearly pots. Those have no calibration marks, so to understand the signal being produced one must observe it with a scope. There’s no power switch; DC comes from a wall wart, and as long as that is plugged in, the unit is on.   This unit generates sine, square (or pulse) and triangle waves from 0 to 10 MHz. It has analog and digital (TTL) outputs. I like the red attenuator button, which decreases the amplitude by 20 dB. The output can be adjusted from a range of -5.5 to +5.5 volts at low frequencies; at 10 MHz that range goes down to +/- 3.6 V.   The offset adjustment range almost lets one get a completely below- or above-zero range. But when those extremes are approached the waveform saturates and distorts, as the following pseudo-triangle wave shows:     A square wave’s duty cycle can be adjusted from 0 to 99%, though at the extremes a slow rise time creates a lot of distortion.   The rise time on the analog output is 35 to 40 ns regardless of frequency. That’s awful for a lot of the work I do, but isn’t far off of some more expensive (couple of hundred dollars) equipment I’ve tested. Poking around, it turns out an Altera FPGA generates an 8 bit digital signal fed to an R-2R network which is followed by a low-pass filter, which explains the sluggish rise time.   With a max frequency of 10 MHz 40 ns may not be a problem for your projects. But consider: 10 MHz is a 100 ns period. As the square wave output gets much above 6 MHz it starts to look a lot like a sine wave. Triangle waves look pretty sine-y above 8 MHz.   The TTL output is much better at 8.5 ns.   Sine waves are uniformly beautiful (with the exception of a small harmonic described below). Square waves below 600 KHz look great, too. But at 1 MHz the duty cycle rapidly varies between about 49.45 and 50.78%, increasing a little as the frequency goes up. You can see both the slow rise time and the jumping duty cycle in this scope shot:     Very strange.   I was a little disappointed by the accuracy of the generated signal. Selecting a 10 MHz sine wave produced one at 10.019878 MHz. But it was almost spot on at 5 MHz.   A counter accumulates pulse counts well, and the unit measures frequency to about 1 count of accuracy. That’s 1 Hz at low frequencies at 100 Hz at 10 MHz.   No manual is supplied, so some functionality is a bit mysterious. Load and save commands exist; probably to save setups. An intriguing log/linear selection didn’t seem to do anything.   At $50 you can’t expect a lot from a piece of test equipment, but I did feed the 10 MHz sine wave into my spectrum analyzer, and found harmonics as seen here:     There are peaks at 5 and 15 MHz which are 52 dB down from the fundamental, and as well as one at 20 MHz, which is 33 dB down from the center. That’s not much energy. Every DDS signal generator I’ve tested has harmonics. My HP 8640B signal generator shows no discernable harmonics, but it uses a cavity oscillator rather than digital synthesis.   Despite the nits, for $50 it’s not a bad little unit, particularly for home use. Figure on pretty good sine wave performance, and decent square waves at low frequencies.

In the past years, I've seen about a bunch of really great April Fools' day spoofs. Who amongst us could forget the classic WOM (write-only memory), which first saw the light of day as a Signetics pseudo-product from 1972 (check out this Signetics 25000 Series 9C46XN datasheet). And then, of course, there was the infamous Black Noise Generator circuit, which purported to be of use when setting up high-end sound systems. Recently, I learned about a smoke re-contractor that can be used to refurbish blown electronic components (I really should have held that back for today, but it was too good not to use). As an aside, the "too good not to use" makes me think of the Queeq episode from the British science fiction sitcom Red Dwarf , but we digress... All of this got me to thinking that there must be myriad April Fool's spoofs of which I remain blissfully unaware. So, what's the very best electronics-related April Fools' joke you've seen in a magazine or with which you have had personal experience?

Over the years I've learned about a bunch of really great April Fools' day spoofs. Who amongst us could forget the classic WOM (write-only memory), which first saw the light of day as a Signetics pseudo-product from 1972 (check out this Signetics 25000 Series 9C46XN datasheet). And then, of course, there was the infamous Black Noise Generator circuit, which purported to be of use when setting up high-end sound systems. Recently, I posted an interesting piece about a smoke re-concentrator that can be used to refurbish blown electronic components (I really should have held that back for today, but it was too good not to use). As an aside, the "too good not to use" makes me think of the Queeq episode from the British science fiction sitcom Red Dwarf , but we digress... All of this got me to thinking that there must be myriad April Fool's spoofs of which I remain blissfully unaware. So, what's the very best electronics-related April Fools' joke you've seen in a magazine or with which you have had personal experience?  

To be sure we are all tap-dancing to the same drum beat (my dear old dad was a tap-dancer on the variety hall stage, so I know whereof I speak), NoC stands for "Network on Chip". My chum George Harper from Bluespec just emailed me to say " Hi Max, I thought you might get a kick out of this Automatic NoC Generator ." George was right ... I did. When you bounce over to this website you discover that you can select the type of topology you wish to implement, the number of routers, the number of virtual channels, the allocation type, the Flit buffer depth and Flit data width, and so on and so forth.   When you click on the Generate Network button, the resulting output is the Verilog RTL corresponding to your network. This resulting code is provided for non-commercial research use only... but I'm sure that they would be willing to talk to anyone who wishes to use this tool for commercial purposes.