butterworth vs bessel filter shape distortion BER

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.

published 4 years ago