![]() You can take a Fourier transform of the filter response, and see your rounded square waves before you build. 3dB at 14MHz, and -12dB per 2x rolloff after that. Chebyshev will give faster rolloff but more phase shift than Butterworth Use for example to build a 3rd order Chebyshev lopass Π filter: Inline inductor is 910nH, and 2 shunt capacitors are 330pF. A Π filter will reject high frequency components better, but give more phase shift but only require 1 inductor. ![]() TimĪ lot later: If you want to smooth out a square wave, what you want is a lowpass filter. This would be the way to go for a signal generator, for example. sometimes poorly terminated cable?), consider using an internal filter, then a buffer amp. Electronic Filter Design Handbook, 4th Ed., Williams and Taylor Handbook of Filter Synthesis, Zverev If the load is not a constant resistance in general (e.g. ![]() Or if it's current-sourced, a one-port-open (shunt C input) type will be needed. If the load is say 50 ohms all the time, all you need is a filter designed for source and load respectively (the source will be fairly resistive if CMOS logic, but if it's substantially lower than 50 ohms (say from a gate drive IC?), consider either ballasting it up with a series resistor, or using a one-port-shorted type filter - such types are found in more complete tables. And since inductors are generally more bothersome than capacitors, you might as well go for an extra pole (4th order) LCLC. From what source? If it's directly on a voltage source like a CMOS output pin, it's not going to appreciate the low impedance (~short circuit) at high frequencies of the pi filter. ![]()
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