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Averaging of a DC pulsed signal

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stcoso:
Hi folks! I have a question that goes on my mind but i'm not 100% sure of the answer i found  ;D.

Let's say that i have a DC pulsed signal that goes from 0V to 2.5V and that repeats itself every 1us.  This signal is not square/sine/triangle/etc... so i can't use Vp value to calculate a mean value (not RMS).

So, i thought that an RC filter with big enough RC constant (>>pulse lenght) could do the trick but i'm not fully convinced ;D.

If this is correct, which is the proper way to choose the R and C values ?


Big thanks in advance.

EEEnthusiast:
Choosing an arbitrarily large RC will increase the settling time of the filter. Choosing a low value will increase the output ripple.
If you select RC = 10xT where T is the pulse rate , then the 3dB BW of the filter would be f = 1/(2 PI RC) = 1/(2 * 3.14 * 10T)
For T = 1uS, this would be 1bout 16KHz, which should be small enough to smooth out a 1uS pulse and settle at its average value.
Settling time would be about 0.35/16KHz . About 22uS.
For better accuracy, use a higher RC and the settling time would increase proportionately.

David Hess:
An RC circuit is the standard way.  An much more complex alternative is to integrate the pulsed DC signal with a reset on every cycle or every several cycles.

macboy:
An RC will work. Beware of accuracy issues though, especially if the high and low drive strength of the source (source impedance) are not equal, such as the case with an open-collector output.   The R in the RC should be much, much higher than the source impedance.

Also note that an RC will always give a triangle wave as the output to a square/rectangular wave input. The peak-to-peak voltage of the triangle can be made small by making the RC long, but it will still be a triangle. If you want something smoother, look at a 2nd order (or higher) filter with a Q factor higher than what an RC can give you (i.e. > 0.5).

T3sl4co1l:
In what way is this "pulsed DC"?  You say it is varying from 0 to 2.5V and is oscillating at, I guess, something like 500kHz or 1MHz (That's "RF" by some standards!).  Can you draw the waveform?

Tim

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