This circuit demonstrates how bessel filters distort the shape less than butterworth filters. We are sending pulses into the 3rd order filter with 2kHz characteristic frequency. Frequency content of a pulse is mostly contained between 0 Hz and 1/T, where T is the duration of the pulse. Notice how the blue signal (butterworth) looks less like a pulse than the green one (bessel - thompson). The overshoot and undershoot totaly ruin time domain characteristics. This effect becomes more visible when the pulses are around 0.5ms or shorter.
This is measured with a error counter. Use the switch to select filter, start the generator by generating a pulse on the upper logic source, reset the counter by pulsing the lower logic source. Adjust the clock frequency, to test bandwidth capabilities.
