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| Why is there a difference in trace width between 1x and 10x probe? |
| << < (3/4) > >> |
| noisyee:
Well, this is a trade-off in basically all kinds of instruments. With input attenuation, you benefit: * Higher input voltage range and better protection * Lower loading effect or VSWR * Lower distortion caused by the input circuits for the same input signal * Possibly more bandwidthAnd you sacrifice: * Sensitivity or resolution * Noise floor or SNR * More likely to pick up interference for a high Z input instrument In this case, 10mV/div with 10X has the same displayed noise floor as 1mV/div with 1X, and 10X probe is more likely to pick up interference. So the trace looks fat and fluffy. If you are dealing with small signal, you would not want the input attenuation in most case! If you really concern about the capacitance loading with 1X probe, try to insert a small series resistor, typically tens of Ω, between the DUT and the probe tip. This would help isolating the capacitance loading, but at the cost of lowering bandwidth. There are some specialized active probes with little to no attenuation for this kind of work, but they are out of most hobbyists' budget. >:D |
| jonpaul:
Tektronix Circuits Concept books Oscilloscope Probe Circuits See Tekwiki and W140 j Jon |
| bdunham7:
--- Quote from: ttodorov on April 14, 2023, 04:40:01 pm ---Can anyone explain why the blue trace looks so ugly, and if there is something I can do to fix this? --- End quote --- The 1X probe will have much higher input capacitance and much lower bandwidth--perhaps 150pF and 3-5MHz. The 10X probe will have better specs and thus is more capable of picking up high frequency noise. You can maybe 'fix' this by engaging the BW limit function and filtering out everything over 20MHz. They still won't look quite the same, but that should make a difference. You can also try using a much faster timebase, perhaps 1µs/div or less, so see what exactly that noise is. Also consider that the 10X probe setting at 10mV/div means that the scope is actually using an input scale of 1mV/div, which is probably its maximum sensitivity. This means that the noise floor will be higher and the trace will be fatter, just not quite as fat an noisy as what you are seeing. There's no easy fix for that and this is why scope front-end noise performance is so important. |
| Fungus:
--- Quote from: bdunham7 on April 15, 2023, 03:02:46 am ---You can maybe 'fix' this by engaging the BW limit function and filtering out everything over 20MHz. --- End quote --- Also try turning on "High Res" mode. |
| ttodorov:
Thank you all for providing your answers! The BW limit on CH2 was enabled - I did not notice any difference. I don't know if I made it clear enough before, but the probes were clamped directly to the coax cable outputting the signal from the function generator (Rigol DG1022A). I used some cut-off resistor leads to make the signal and ground connections respectively. So there were no additional components and/or power supplies connected to the probes. The termination on the generator output was set to HighZ since I don't think that the cheap Rigol DS1054Z has 50 ohm input impedance matching. I also turned off everything else around me that I could, even the lights. The only thing I did not think to turn off was my WiFi access point in the same room, so I have no idea if that can produce enough interference to be picked up by the 10x probe like that. Up to now I have dealt mostly with GPIO or PWM signals where 1x probe was always enough. This is the first time for me dealing with an amplifier circuit and thus I noticed the behavior only now... |
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