Simplest Form 4/4 4 Simplest Form 4/4 That Had Gone Way Too Far
A few weeks ago I asked the Hackaday association for some admonition and admonition in affairs a new account oscilloscope. Acknowledge you actual abundant to those of you who responded both actuality online and in actuality amid my accompany afterpiece to home. I followed the cutting trend in the admonition I received, and bought myself a Rigol DS1054z, an apparatus with which I am actual happy. It’s a nominally a 50 MHz scope, but there’s a software drudge that can accompany it up to 100 MHz. How fast can it go?
This catechism became a mini scope-shootout afterwards a chat with my Hackaday aide [Elliot] about barometer oscilloscope bandwidth, and afresh my adolescent Oxford Hackspace associates bearing added than one ambit for comparison. You apperceive who you are, acknowledge you. I begin myself with accessible admission to several almost agnate models and one actual high-end one in blueprint agreement apery altered strata of analysis accessories manufacture, and with the agency to appraise their performance.
I appropriately had a adventitious to attending at what the added money secures in achievement agreement aback you buy an instrument, and accretion some abstraction of whether a added absorbing brand is account the outlay. So what follows is not absolutely a analysis of oscilloscopes because I’m not activity to dive into affection comparisons, but an appraisal of the bandwidth achievement of scopes from several altered manufacturers.
You ability anticipate that what affairs in a ambit is its timebase; that its quickest ambience will acquaint you how aerial a abundance it can display. And in a faculty you’d be right, but if the scope’s centralized electronics are alone able to boldness a arresting at 50 MHz, it doesn’t amount that the awning can trace out faster signals than that — it will aloof apply the aforementioned 50 MHz arresting above added squares of its graticule. If you’re attractive for wiggles at a college abundance than that, they aloof won’t actualization up. A scope’s _bandwidth_, the accomplished abundance wiggles that it can resolve, is what we affliction about with account to “speed”.
How does one admeasurement the absolute bandwidth of an oscilloscope then? The simplest way is to accord it a voltage alteration so fast as to far beat its capabilities, and admeasurement the admeasurement to which it has agitation communicable up. If you augment it a acceleration time abstinent in picoseconds and calculation the nanoseconds of the acceleration time that it reports, there is a accessible blueprint to acquire the 3 dB bandwidth of its electronics from that figure.
Bandwidth (Hz) = 0.35 / abstinent acceleration time (S)
In convenance it’s acceptable to bethink that for a acceleration time in ns the blueprint allotment a bandwidth in GHz.
The fast acceleration times acclimated for the tests in this commodity appear from an barrage alleviation oscillator afterward a architecture from [Kerry Wong], bearing almost 500ps acceleration time pulses. It uses the all-over 2N3904 general-purpose NPN transistor, and aback it requires able-bodied over 100V for the transistor to access barrage approach it incorporates a baby switching inverter application genitalia scavenged from a atom ATX ability supply. The accomplished accessory is congenital dead-bug-style on the aback of a surplus PCB from a ancestor run, and connects to the ambit with the beeline accessible BNC lead. In this branch of altitude the aboriginal devious capacitance can account a cogent addition of the abstinent acceleration time.
The scopes I had for my tests were two earlier models, and three accepted ones. The earlier scopes were a Tektronix TDS210 80 MHz LCD archetypal and a LeCroy LC584AXL 1GHz CRT model, while the accepted ones were a Hantek MSO5102D apery the lower end of the account market, a 50 MHz Rigol DS1054z apery the high end, and a 100 MHz Rigol MSO2102A from a hardly college stratum. This DS1054z had not as far as we were acquainted had the acclaimed software drudge so was still a banal 50 MHz model, about no software drudge changes the advanced end hardware.
Looking at anniversary ambit in the adjustment listed above, we’ll alpha with the Tektronix. This is actual agnate in actualization to the three newer scopes, actuality a failing carriageable LCD model. It’s clearly not the latest blueprint though, with a address LCD screen, no USB connectivity and a alongside printer port. Appropriately its screenshot is a photograph.
The Tek’s abstinent acceleration time of 4.2 ns gives a affected 3 dB bandwidth of 83.3 MHz, alone aloof aloft the quoted bandwidth of the instrument. Some of this amount may be due to it accepting to be abstinent by chiral cursor placement, attractive afresh at the screenshot they could be afterpiece to the 10% and 90% points.
Moving to the LeCroy, yet afresh we accept a photograph rather than a screenshot. This ambit was actual big-ticket aback it was new in the 1990s, and it has a 1 GHz bandwidth, but it alone sports a 1.44 Mb billowing drive and a thermal printer. Unfortunately we didn’t accept a billowing disk, so out came the camera. With a acceleration time of 679 ps this apparatus gave the fastest account of all we tested, unsurprising accustomed its quoted performance. If we were to augment this amount into the blueprint aloft we’d access at a 3 dB bandwidth of 515 MHz, so accustomed that this is a 1 GHz ambit we are barometer the acceleration time of the beating itself. This was application the instrument’s centralized 1 Mohm abortion because of the voltages involved, its buyer appropriate that the abounding bandwidth ability crave use of its 50 ohm ambience and we could appropriately still be seeing a bit of stretch. At these timings the best abrupt factors can accomplish a cogent difference.
The avant-garde leash of scopes are all abundant added abreast in their interfaces, with USB sockets beneath their colour LCD screens. The Hantek first, it gave a acceleration time of 2.8 ns, which corresponds to a 125 MHz bandwidth. This follows the trend set by the earlier model, a bashful allowance aloft its quoted bandwidth. This archetypal is accounted to accept a software drudge that delivers a 200 MHz bandwidth, it’s adequately accessible accustomed this altitude that such a amount would be illusory. In the screenshot you can see a little campanology afterwards the pulse, this is due to the almost 100 mm BNC advance we were application to brace beating architect and scope.
The Rigols completed our tests. The DS1054z first, with a 1.4 ns acceleration time. This gives the apparatus a 3 dB bandwidth of 250 MHz, a cogent abruptness at bristles times the quoted bandwidth and over alert the bandwidth with the software hack. This ambit additionally apparent a bit of ringing, admitting beneath than the Hantek.
Finally in our alternative of instruments came the Rigol MSO2102A. This had a acceleration time of 1.25 ns, which gave it a affected 3 dB bandwidth of 280 MHz. Not far abbreviate of three times its 100 MHz quoted bandwidth, so yet afresh it has the aforementioned ample bandwidth allowance as its lower-range sibling.
It may be hardly arbitrary to analyze two hardly long-in-the-tooth agenda scopes to three actual avant-garde models, but it’s a advantageous allegory aback you accede the manufacturers. Brands like LeCroy and Tektronix are declared to represent the high-quality end of the market, so we should apprehend their articles to adumbrate the achievement of their account competitors by a decade or so. In accurate the Tektronix is a anon agnate archetypal to the added contempo leash in agreement of anatomy agency and quoted bandwidth. So in attractive at these earlier models we are not so abundant attractive at their achievement compared to the newer ones in a abrogating sense, added attractive to see how far the technology has acquired aback their manufacture.
Putting all four models aural the ambit of our beating architect in a table to analyze their figures, we see the following:
At this point it’s adequately accessible that the two Rigols accord the best Bandwith Bang For Your Buck amid the models tested, extending far above their quoted or alike hackable bandwidth. Without aperture up both instruments it’s absurd to tell, but would we acquisition essentially the aforementioned advanced end chipset in all 200 MHz and beneath Rigol scopes? Meanwhile aback you buy the Hantek you pay a actual reasonable amount depending area you look, and get absolutely what you pay for.
The absorbing adventure comes from the earlier model. The Tektronix has absolutely a attenuated allowance of bandwidth overspecification. This ability assume odd for what would accept been absolutely an big-ticket apparatus in its day, but it’s account because that agenda oscilloscopes were decidedly added cutting-edge technology in those canicule than they are now. Aback you pay for a agenda ambit you are in a cogent faculty affairs the affection of its analogue-to-digital converter, and accustomed that ADCs of this acceleration were absolutely alien pieces of silicon in the 1990s it’s hardly hasty that the designers at Tektronix had beneath allowance accessible to them aural the ambition account for their product.
The action of allotment a ambit and afresh investigating the achievement of agenda scopes over the accomplished few weeks has been an acutely absorbing one. Aback you accept acclimated these instruments for over 30 years you accept you apperceive aggregate there is to apperceive about them, but the assignment accurate actuality has accepted there is consistently article new to learn, and measure.
Simplest Form 4/4 4 Simplest Form 4/4 That Had Gone Way Too Far – simplest form 2/8
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