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larry_tye
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 « on: February 13, 2013, 04:22:57 04:22 »

I design a scope using EMWIN software in GUI , it took 1uS to input the sample data and took 13uS to draw the graph . In this speed is it sufficient fast enough to process 20M bandwidth of signal ??
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optikon
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 « Reply #1 on: February 13, 2013, 04:51:25 04:51 »

I design a scope using EMWIN software in GUI , it took 1uS to input the sample data and took 13uS to draw the graph . In this speed is it sufficient fast enough to process 20M bandwidth of signal ??
No.
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I can explain this to you. I can't comprehend it for you.
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 « Reply #2 on: February 13, 2013, 05:40:14 05:40 »

http://en.wikipedia.org/wiki/Nyquist_frequency
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piclover
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 « Reply #3 on: February 13, 2013, 06:32:29 18:32 »

1 uS sample rate is OK for 500 kHz BW. U need sample rate freq of minimum 2x BW.
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Gallymimu
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 « Reply #4 on: February 13, 2013, 09:46:32 21:46 »

Nyquist theorem is great, but, notice that decent oscilloscopes sample much higher than 2x the bandwidth.  10x is a good place to start to avoid any scaling and processing needs.  Fancy scopes with complex sampling algo's will drop to as low as 3-5x the bandwidth.  It also makes things like anti-aliasing much easier too.

Here's a nice white paper from agilent justifying going as low as 2.5x the bandwidth, but not all the way down to 2x (http://cp.literature.agilent.com/litweb/pdf/5990-9923EN.pdf)
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DreamCat
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 « Reply #5 on: February 15, 2013, 04:35:06 04:35 »

I think you should better to consider the speed of LCD display, and then is amount of screen pixel points.
for the Nyquist_frequency, I think it means sine-wave only.

but if you only want to display square wave or logic pulse wave, it seems that no need to consider Nyquist_frequency.
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May be I expressed the wrong meaning, sorry for my bad english. Please correct it for me if you can.
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 « Reply #6 on: February 15, 2013, 05:21:33 05:21 »

<sigh>

All of you are confusing sample rate with bandwidth.

He gave the sample rate, not the signalpath bandwidth.

On repetitive signals you can get away with undersampling with a sampling scope.

If it's a realtime scope, then Nyquist holds.

He didn't say which kind of scope he was building or the nature of the signal....

NOT ENOUGH INFO
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