Why is RAM so small ?

Thread Starter

DarthVolta

Joined Jan 27, 2015
389
Looking around at new DSO's and AWG's, I see them flaunt like 1, 5, 20 MegaBytes of RAM. So how expensive are the RAM chips they are using ? Well we've had computers with 100's of MB of RAM for over almost 2 decades (icr).

Some types of RAM are expensive I know, so why are they using so little ram is what I'm wondering. Is it they just don't need that much, and it's not holding them back anyways ? I bet it can't be the cost, because everything EE costs a fortune, so if money could fix it they'd do it ??? IDK
 

nsaspook

Joined Aug 27, 2009
7,181
Much of that very fast acquisition memory is embedded into custom chips. Static most likely, that's not cheap on the die cost scale.
Although intuitively you might think that deeper is always better, using deep memory means making tradeoffs when using many scopes on the market today. First of all, scopes with deep memory are typically priced higher. Second, acquiring long waveforms using deep memory requires additional waveform processing time. This typically means waveform update rates will be reduced, sometimes significantly. For this reason, most scopes on the market today have manual memory-depth selections, and the typical default memory depth setting is usually relatively shallow (10 to 100 k). If you want to use deep memory, then you must manually turn it on and deal with the update rate tradeoff. This means you must know when it is important to use deep memory and when it is not.
https://www.keysight.com/us/en/assets/7018-07618/flyers/5990-6735.pdf
https://www.sciencedirect.com/topics/engineering/digital-storage-oscilloscope
 

Thread Starter

DarthVolta

Joined Jan 27, 2015
389
Ok so they aren't using leftover NOS from 1990's soundcard RAM LOL


IDK about DACs and RAM really. My Tek2430A was 1 of the 1st DSOs, when doing single shot triggers, I fill it's ram pretty easy.

But yeah whatever relates the memeory to the resolution and sampling rate etc, I guess they don't need a whole lot, and most people don't need to record hour's worth of data into RAM
 
Last edited:

nsaspook

Joined Aug 27, 2009
7,181
Ok so they aren't using leftover NOS from 1990's soundcard RAM LOL


IDK about DACs and RAM really. My Tek2430A was 1 of the 1st DSOs, when doing single shot triggers, I fill it's ram pretty easy.

But yeah whatever relates the memeory to the resolution and sampling rate etc, I guess they don't need a whole lot, and most people don't need to record hour's worth of data into RAM
Nice old scope. I just fixed one of those. The NVRAM has a limited battery life.
https://forum.allaboutcircuits.com/threads/tek-2432-nvram-replacement.165205/
 

tautech

Joined Oct 8, 2019
89
But yeah whatever relates the memeory to the resolution and sampling rate etc, I guess they don't need a whole lot, and most people don't need to record hour's worth of data into RAM
Stated memory is not always the total available. Eg. the SDS1104X-E you're looking at getting has some 50+Mpts available for History mode. However as nsaspook pointed out memory depth is managed in order to preserve wfps rate so to minimise blind time.
To make best use of the total memory available and utilise the strengths of a DSO it's best to use a timbase setting that has high memory depth and examine the waveform capture with a faster timebase setting. However doing this with non repetitive signals requires use of the right trigger settings to capture the point of interest like a Runt or Glitch and then examine the events pre-trigger to find what caused it.
The most powerful tool suite in a DSO is the selection of trigger types coupled with the users ability to know how to use and apply them.
 
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