Samplerate

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30 Dec 2006
Posts:

Hi

I am trying to decide which kind of scope to buy, a Cleverscope or a non-PC (ordinary) scope.
I can see from the comparison table, that the Tektronix TDS2012 has a samplerate of 1000 Ms/s. I guess this means it can sample a 100MHz squarewave at 10 points, which gives a good resolution. However, the Cleverscope (and most other PC scopes I have seen) ""only"" has a 100 Ms/s samplerate.
What are the pros/cons of this higher samplerate? Or are there a reason, besides cost savings, why other scopes, including the Agilent 54622, use a lower rate of 100 to 200 Ms/s (i.e other parameters benefitting from a lower samplerate)?

Also, the TDS2012 samplebuffer of only 2.5k versus 4000k in Cleverscope. Why this big difference? Is the Tektronix scope meant for other measuring purposes than Cleverscope? Won't the 2.5k buffer give some limitations on the usefulness of the high 1000Ms/s samplerate?
Sorry for all these beginners questions:-)

If I order a Cleverscope through one of the retailers now, will it then be the new A version, or isn't it available yet?

Best regards & Happy new year,

Peter

31 Dec 2006
Posts: 396

Hello Peter,
Thanks for the question. You are quite right, the TDS2012 can sample a 100 Mhz signal, and define 10 points. It can also digitize single shot measurements at this rate, and capture events 10ns long. Cleverscope can only digitize at 100 Ms/s, so you cannot see single shot pictures of this duration. Cleverscope, and many other scopes do offer equivalent time sampling of repetitive signals, so you can capture a continuous signal of 100 Mhz frequency. Cleverscope offers 200ps resolution under this circumstance, but ETS is useless for single shot capture. From this you can see that for short time duration events you need a high sample rate, and the TDS2012 is a better bet.

However, high speed (as in 1GHz) memory is very expensive, and so the TDS2012 is limited to 2.5k samples. This yields a total time duration of 2500 ns, or 2.5us. Once you set the time duration to longer than this (which is equivalent to 10 divisions of 250ns/division), the sample rate will be reduced. Cleverscope, on the other hand, uses a much larger, less expensive memory. At 100 MSa/sec (10ns per sample), and 2MSample long record (the 4Msamples are split into two or more frames for reasons explained in other posts), we can record 20ms before reducing the sample rate. The TDS2012 will be sampling at 20ms/2500 = 8us per sample. So at this duration, the Cleverscope is 800 times faster. So you can see there is a big trade off between memory size and sample rate going on here. If you want to mostly look at very short duration events, a TDS2012 is better. If you mostly want to look at events lasting 50ns or longer, a Cleverscope will give you more flexibility.

In many circumstances a long record makes it easier to find the problem events. With a Cleverscope you can (and some of our customers do) look at every switch transition of a 300 kHz switching power supply for a complete mains cycle before an over current failure, for example. You cannot do this with a small memory oscilloscope.

All Cleverscope delivered from now on will be CS328A.

Happy New year!
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