Re: Digital Osci and Logic Analyzer

Abstract Dissonance <Abstract.Dissonance@xxxxxxxxxxx> wrote:
How complicated is it to create a simple pc based oscilloscope and logic
analyzer(excluding the pc software)?

Does it just consist of getting a ADC and interface for sending the data to
the pc? I'm looking at trying to make one in a similar way to what is done
on this site:

http://www.fpga4fun.com/digitalscope.html

You could grab an development board from Altera, Xilinx etc.. that contains
an ethernet interface. Maybe you can find a pre-made ADC module aswell.

On a note some fgpa have 1 Gbps ethernet builtin..

The other option is a pcb board with the components you want. Althought that
would be complicated.

Lets suppose I decide to buy a 1Gsps ADC(which isn't going to happen any
time soon) and I have a probe that works properly with the ADC. How would I
go about storing/streaming all those samples? This would require a memory
chip be able to work down at 1ns or so? I was thinking I could use several
gigs of pc memory in parallel to reduce the latency and increase total
sample size to a few seconds... is this possible? What about encoding for a
digital stream? do something like rle on the bit stream where 01 one would
store 2 bits as one and its number of repetitions? (need to use 2 bits
atleast so things like a clock signal are encoded efficiently)

I'm kinda curious to how high speed logic analyzers overcome some of these
problems?

You could select the cheapeast memory per byte. Then use them in parallell to
compensate for any speed compromise.
Unless you simple download it all to computer. Ethernet could be convinient
for this.

Another thing I wanted to know is how digital logic signals are "sampled" in
logic analyzers? Surely one doesn't need anything more than a 1-bit ADC to
convert the line signal? (therefor one doens't even need an ADC since it
would act more like a buffer than an real ADC?)

They most likely have an schmitt trigger at input. Possible some level
converter.

.

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