PicoScope 7 Software
Available on Windows, Mac and Linux
Picsoscope Usability Problem: Bad SNR with Unipolar Input Signal?
Picsoscope Usability Problem: Bad SNR with Unipolar Input Signal?
Dear All,
Opposed to audio signals, which are almost always symmetrically centered around zero (=no DC offset) in power electronics almost every signal is unipolar in its nature and therefore asymmetric in reference to the zero-Volt return (=GND). One could also say the signal has a significant DC offset.
I own a Picoscope since several years and always had problems scoping unipolar signals with it (PicoScope 6 software on Windows), what is the best scope/channel setup?
Practical example: Probing the switching node of a 12V output buck regulator.
At work I use a fancy standalone scope from a known major brand. In this case I would set the channel DC-offset to -6V and vertical resolution to 2V/DIV. This way, the waveform is using most of the vertical screenspace, whilst keeping some headroom for over-/undershoot. This way the displayed waveform is very informative and also helps to improve the SNR (assuming that the displayed vertical fullscale corresponds to the fullscale input range of the sampling ADC).
At home, using my 5444B.... when setting the DC-offset to -6V and the vertical range to +-10V i get a "Channel Overrange" error. So I use the +-20V range and no superimposed DC-offset (=0). But now the waveform does only use half of the available screenspace (not very informative, small laptop screen) and I am not really sure about the ADC-utilization. I currently assume that only half of the sampling ADC input range is used, which leads to very bad SNR.
One solution would be AC coupling, but in power electronics DC metrics of a waveform is THE key-information.
Actually because of this issue I would not recommend buying a PicoScope to anyone. But maybe I have the wrong setup? What is your advice?
Kind regards
nano
Opposed to audio signals, which are almost always symmetrically centered around zero (=no DC offset) in power electronics almost every signal is unipolar in its nature and therefore asymmetric in reference to the zero-Volt return (=GND). One could also say the signal has a significant DC offset.
I own a Picoscope since several years and always had problems scoping unipolar signals with it (PicoScope 6 software on Windows), what is the best scope/channel setup?
Practical example: Probing the switching node of a 12V output buck regulator.
At work I use a fancy standalone scope from a known major brand. In this case I would set the channel DC-offset to -6V and vertical resolution to 2V/DIV. This way, the waveform is using most of the vertical screenspace, whilst keeping some headroom for over-/undershoot. This way the displayed waveform is very informative and also helps to improve the SNR (assuming that the displayed vertical fullscale corresponds to the fullscale input range of the sampling ADC).
At home, using my 5444B.... when setting the DC-offset to -6V and the vertical range to +-10V i get a "Channel Overrange" error. So I use the +-20V range and no superimposed DC-offset (=0). But now the waveform does only use half of the available screenspace (not very informative, small laptop screen) and I am not really sure about the ADC-utilization. I currently assume that only half of the sampling ADC input range is used, which leads to very bad SNR.
One solution would be AC coupling, but in power electronics DC metrics of a waveform is THE key-information.
Actually because of this issue I would not recommend buying a PicoScope to anyone. But maybe I have the wrong setup? What is your advice?
Kind regards
nano
Last edited by nano on Mon Oct 26, 2020 8:53 am, edited 1 time in total.
Re: HowTo? Probing a asymmetric Signal?
This thing really bugs me.
What is the right way to probe a purely asymmetric signal? Always relying on Zoom is no real solution for me.
Kind regards
nano
What is the right way to probe a purely asymmetric signal? Always relying on Zoom is no real solution for me.
Kind regards
nano