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| Bandwidth of Logic Analyzer |
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| magic:
--- Quote from: NaxFM on August 05, 2019, 06:54:56 pm ---So, let me ask again the starting question in a (I hope) more clear way. Does the 100MHz bandwidth of the digital discovery means that I can reliably visualize a 100MHz square wave at 50% duty cycle? --- End quote --- I'm afraid you will only get this answer from somebody who owns that hardware. I can testify that analog bandwidth can be an issue in those USB gadget analyzers. I used to have one, it had some RC networks for input protection and didn't work at bit rates faster than about 30% of its sample rate. I don't remember if the manufacturer specified it for input BW or not and how that spec (if any) translated to the maximum bitrate I observed. If I were to guess, I would say that 100MHz is the -3dB point. A 3.3Vpp square wave still has some significant 100MHz sine component (say, quite likely more than 2Vpp) so even after 1.4x attenuation we are still left with 1.4Vpp swing, which will likely be sufficient for reliable detection by the input buffer, if it uses the usual CMOS threshold of 50% VCC. --- Quote from: NaxFM on August 05, 2019, 06:54:56 pm ---Inviato dal mio Moto G (5S) Plus utilizzando Tapatalk --- End quote --- Yeah, message posted with Firefox from my laptop computer :P |
| radiolistener:
--- Quote from: NaxFM on August 05, 2019, 06:54:56 pm ---Does the 100MHz bandwidth of the digital discovery means that I can reliably visualize a 100MHz square wave at 50% duty cycle? --- End quote --- no, you can only visualize 100 MHz which is synchronized with sampling oscillator of the analyzer. If it will not be synchronized, or if the frequency will be different (even for 0.00001 Hz or less), you will get a jitter. The mistake will depends on sampling frequency. Higher sampling frequency = smaller jitter. But sampling oscillator has it's own jitter, which will affect results for high frequency. So, all depends on what precision you're needs :) According to the site, Digital Discovery works at 800 MS/s. It means that you can capture up to 400 MHz frequency. But it doesn't means that it will be nice waveform. It just means that you can still measure frequency of the signal up to 400 MHz. All frequencies above 400 MHz limit will be measured incorrectly. They will be captured with aliases. The jitter will be about 1.25 ns. Your 100 MHz signal has 5 ns pulses. But you will see random duty cycle on captured waveform due to the jitter. It will vary within range 37-63% duty cycle. |
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