Algorithm for simulating phosphor persistence of analog oscilloscopes

Summary

Background to phosphor displays and analog oscilloscopes For all of you that have used analog oscilloscopes or other equipment with a phosphor display knows how beautiful the image can be from such displays. The color grading, which naturally occurs due to the persistence in the glow from the phosphor, also acts as a useful measurement on the signal integrity, such as how much noise there is and the shape/modulation of the underlying signal. Photograph of the display on a COS6100A analog oscilloscope using phosphor of type P31 (by Mikael Altemark) Modern oscilloscopes tries to simulate the same “look” by sampling large amounts and data which is processed and color shaded in a similar manner. However the resulting image is always inferior in both resolution and dynamic range due to the limitations in processing power and display technology, giving rise to aliasing problems when using time-base which is not optimal for the measured signal. At the time of writing this document (2016) high-dynamic-range displays and TVs are only starting to become available to the general public. However they are not yet available on oscilloscopes or other similar measurement equipment. Screen capture of an AM modulated signal on a modern Keysight Infiniivision 4000-series oscilloscope claiming to have digital phosphor display/technology. Comparing the digital image to a similar AM modulated signal on an analog oscilloscope immediately shows the large difference in color intensity when the signal overlaps. Another important aspect is the lighter color around the edges of the waveform, due to that a sine wave spends more time at the top and bottom than in the middle where the rise time is much faster. Thus even though we can not see the carrier wave in the photo below we can deduce that it must be a sine-wave or something very similar. If the carrier was a square-wave then there would not be any color in the middle of the larger waves, since a square wave spends all its time at the top o...