Project update 2 of 12
One important characteristic of an oscilloscope is the level of internal noise generated by its analog front-end and AD conversion process. Noise affects accuracy, especially when measuring low amplitude signals. Let’s take a look at how ScopeFun performs in this regard.
Before taking measurements we need to eliminate the influence of external noise sources. We do here by setting the oscilloscope input coupling to GND. Then, to obtain the measurements described below, we set the oscilloscope to capture frames of 10,000 samples at 250 MSPS. We measured both RMS-AC and peak-to-peak voltage values for every frame. The final result is an average value of several consecutive captured frames:
|Range [V/div]||Average Noise RMS-AC [mV]||Average Noise Vpp [mV]|
While this is a relatively low level of noise, we can lower it even further by doing some post-processing of captured samples. If the signal of interest is repetitive, we can implement a simple function to average samples (and noise) between different frames. If the signal of interest is not repetitive, we can average between consecutive samples, effectively creating a filter. Doing so will reduce our bandwidth, however. One alternative that is usable at lower sampling speeds is to apply a combination of oversampling and averaging, which effectively increases our vertical resolution to over 10-bits.
We have measured ScopeFun’s baseline noise levels and provided some methods on how to reduce noise further through post-processing. Software post-processing functions are not difficult to implement, and we may add one to the next ScopeFun software release.