Say you want 1ghz bandwidth, you'd need to sample at at least 2ghz, this is where you run into problems, you can't just dump that into DRAM (you can get about ~100m/sec (100mhz) requests from DRAM, they're faster than this at sequential transfers once you've opened the page) - so you'll need to buffer there.
Not true. The bandwidth and sampling rate are independent.
Examples:
- SDR. Even the cheap dongles capture 1.5GHz waveforms, and their sampling rate is several orders of magnitude lower
- TDR. My 1970s Tek 1502 displays <140ps risetimes and its sampling rate is <100kS/s
- Scopes. One I used many decades ago is the HP54100A: 1GHz/350ps, 40MS/s
- X-Y plotters. In the mid 70s I saw an experimental sampling scope with >1MHz bandwidth that used an XY pen-plotter as an output device.
There are many many other examples.
its funny you have a habit to get into disagreement with people and giving lecture philosophically about "in context" discussion, strawman fallacy etc (in other thread) without realizing you are the one you are lecturing about. i browse this thread quickly and nothing talk about sampling scope (which is a specialized scope),
You think a Rigol DS1054 or the many equivalent low end scopes are "a specialised scope"? I don't think many people would agree.
you cant bode plot with sampling scope.
Yes you can. It is standard on the entry-level Digilent Analog Discovery, and I believe it is an option on many other low-end scopes.
With skill and imagination you can do it on
any scope, snalogue or digital, with or without digital post-processing. You might find it convenient to have a numerically controlled oscillator or voltage controlled oscillator (with log scaling), plus an Arduino's ADC, but you can do it.
people talked about nyquist criteria (2.5X BW to be exact, not 2X) which is what we understand normally as what a normal scope do, and then you wandered off to suggest 1GHz BW with KSps scope,
So you discount commercial scopes such as the HP54110A 1GHz bandwidth, 40MS/s? That was a "normal" scope in its day, albeit top of the range.
Or the Tektronix 11801 with SD-22 plugin: 12.5GHz, 200kS/s. I know people actively creating advanced electronic products using those.
Your definition of "normal scope" appears to be "scopes that I think of using", which is rather limiting if you are trying to understand the minimum necessary to make a useful and usable scope.
and how unimportant is trace length and propagation delay is in GHz domain. its just out of context, and even incorrect in some context... no need to further mess the already complicated subject (now i quote you fully so you have less chance to invent strawman argument on me
)
I've made no such statements, of course.
I have stated that you can make the traces so short that their length is unimportant - and proved that with a photo of a commercial product.
btw, i agree with tautech, OP is going into rabbit hole, or worse a worm or black hole. if you really want to waste your time you can dig i also created a thread like this to ask many years ago (while the spirit is high) and then i never made the first step, knowing more (or just a little bit) of what i actually dealing with... if you think you can beat the already cheap Rigol or Siglent and their in-house engineers, then imho you are delusional. lest if you want to talk about saving your pocket money. and later after that, i was thinking about the 10GSps or greater DSO segment where we dont have cheap option yet, maybe i can implement Rigol brilliant idea of interleaving 10x 1GSps ADC? but when i browsed digikey for the price, i closed the browser and never went back to the idea again. going fishing is much much better things to do for the sake of your brain and health.
I'll leave the OP to decide what is relevant for him. It would be arrogant for me to speak for him.
I too think the OP is biting off more than they can chew. I suspect he does realise that, but he is enjoying the conversation, viz
I'm following (or trying to follow) your discussion with the utmost interest.
From what little I can infer about the OP, he is having fun understanding what's in a scope and the many imaginative ways you can build them. Whether he builds one is a separate issue.
Having fun while pushing the boundaries of his understanding and capabilities?
I like that attitude 