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Tektronix 1-3 GHz touch screen color DSO back in 1989 !
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David Hess:

--- Quote from: Wuerstchenhund on August 21, 2017, 08:57:52 am ---Well, it doesn't look to be a true real-time scope either as 20 MSa/s is hardly enough to capture the 1Ghz BW of the 11A71 amplifier plugins on the photo.
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It is not a real time oscilloscope although the display is updated in real time for which 20 MSamples/second is plenty fast.  Tektronix never claimed it was a real time oscilloscope and DSOs with sample rates to support a Nyquist frequency greater than their bandwidth were the exception back then.

A 2230 is 100 MHz but only has a 20 MSample/second sampling rate but that does not make it a sampling oscilloscope.  A 7854 is 400 MHz but only has a 500 kSample/second sampling rate and might be considered the predecessor to the 11400 series but it is not a sampling oscilloscope either.


--- Quote from: Hydron on August 21, 2017, 07:25:36 am ---Ok, so that would give it a real-time BW of roughly 8Mhz in single channel mode, 2Mhz in two channel mode and 1Mhz in 3 channel mode, the full BW seems to be available in ETS mode only => looks a lot like a sampling scope.
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So what distinguishes a sampling oscilloscope like the HP 54120B or Philips PM3340?

1. The sampling gate width is much less than the sampling gate time constant so the input sampling capacitance never has time to charge to the input voltage.  Another way to put this is that the sampling efficiency is below 1; usually it is a lot lower than 1.

2. As a consequence of 1 above, the input is roughly integrated over the sampling gate width producing a non-linear frequency response which follows the sin(x)/x curve with a first null at the reciprocal of the sampling gate width.  The familiar bandwidth = 0.35 / transition time rule does not apply.

3. To take advantage of the extremely high bandwidth this produces, there are no amplification stages between the sampler and the input.  (1) Usually there are no attenuation stages, delay lines, or other networks either.  Even a length of transmission line would compromise the potential bandwidth and often does.

(1) I know of one exception to this.  High input impedance samplers include a *low* frequency buffer before the sampling gate to remove accumulated charge (2) from any input capacitance which could not otherwise be discharged by the high input impedance.  High frequencies bypass this buffer.  As far as I know, Tektronix was the only one to make high input impedance samplers.

(2) I think the problem here was kickout from the sampling strobe charging the input capacitance causing the DC level to shift.  The Tektronix 50 kilohm samplers (Tektronix S-3) did not need a low frequency buffer but their 1 megohm samplers (Tektronix S-5) had one.
snoopy:
I think the correct term is sub-sampling scope or equivalent time sampling which requires repetitive waveforms for equivalent sampling rates greater than the ADC sampling rate !
David Hess:

--- Quote from: snoopy on August 21, 2017, 01:40:30 pm ---I think the correct term is sub-sampling scope or equivalent time sampling which requires repetitive waveforms for equivalent sampling rates greater than the ADC sampling rate!
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The correct term in place of what?

There is nothing to preclude DSOs (digital *storage* oscilloscopes) with real time sampling from using equivalent time sampling and many do to achieve even higher sampling rates so the term equivalent time sampling is ambiguous in distinguishing them.
Johnny10:
I use the DSA602 and 602A as my everyday scopes.

Wuerstchenhund:

--- Quote from: David Hess on August 21, 2017, 01:21:33 pm ---
--- Quote from: Wuerstchenhund on August 21, 2017, 08:57:52 am ---Well, it doesn't look to be a true real-time scope either as 20 MSa/s is hardly enough to capture the 1Ghz BW of the 11A71 amplifier plugins on the photo.
--- End quote ---

It is not a real time oscilloscope although the display is updated in real time for which 20 MSamples/second is plenty fast.
--- End quote ---

A digital scope is either a real-time scope (aquires the waveform in real-time) or a sampling scope (i.e. it acquires the waveform over multiple acquisition passes).


--- Quote ---A 2230 is 100 MHz but only has a 20 MSample/second sampling rate but that does not make it a sampling oscilloscope.  A 7854 is 400 MHz but only has a 500 kSample/second sampling rate and might be considered the predecessor to the 11400 series but it is not a sampling oscilloscope either.
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Both the 2230 and the 7854 are are analog/digital combi-scopes which both reach their analog BW in repetitive sampling or analog mode only. You're right that none of them are true sampling scopes as they are combi scopes with an analog and a digital mode.


--- Quote ---So what distinguishes a sampling oscilloscope like the HP 54120B or Philips PM3340?

[....]


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Back in the old days, Tek used to define1 a sampling scope as a scope that put the sampler in front of the amplifiers and a DSO as a scope that has amplifiers in front of the sampling stage. But this was never an universally accepted definition and wasn't even correct as not all sampling scopes followed Tek's definition (i.e. LeCroy WaveExpert and I believe also the Agilent/Keysight DCA-J/-X). HP also had some sampling scopes (i.e. the 54501A) which didn't follow Tek's rule as well.

Today, a sampling scope is generally considered a fully digital scope that acquires its waveform over subsequent acquisitions to reach its full analog BW. It doesn't matter what sampling technique is used (random or sequential), or how it is actually implemented.



1 http://www.tek.com/sites/tek.com/files/media/media/resources/Sampling%20Oscilloscope%20Techniques.pdf
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