The goal is SAY NO TO FIRST ORDER RC FILTER , may be start with analog filter approach. The Bessel filter and Gaussian filter both have good phase characteristic, that should improve the time domain response, make them suitable for pulse shaping application. There's are good filter design tools out there, Analog devices/TI both provide web based tools, but TI required account login.
The Analog Devices ANALOG FILTER WIZARD hided some filter terminology such as Butterworth/Chebyshev/Bessel filter type, in another words, they use Fewest stage/Fastest settling to abstract out the optimization goal. Low pass filter with 5kHz cutoff frequency specification is picked.
It's a very relax frequency response specification, so it only takes 1 stage of opamp, it also give option for optimize for noise or optimize for power. Low noise is chosen in this test. Sallen key topology is default.
Simulation in LTSpice, using LT1797 opamp.
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The filter was firstly implemented using LM358 general purpose opamp, but it give weird spike in the rising of the pulse, then it is replaced by LMH6646, which give a nice waveform, the reason why LM358 is not working is not yet understood. The waveform match with the simulation. The waveform is more symmetric than a first order RC filter, nice.
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