Chris

Fortunately there is another way you can do this. Use the input pulses as a gate to a high frequency counter. Now, the number of counter pulses in the gap between 2 input pulses will indirectly yield the frequency of the input waveform. Here I am assuming that the input is a repetetive shape, which is valid since you mention a speed sensor. You can get very good fractional frequency results depending on how fast the counter is clocked. I'll leave out the workings of it for now.

A caveat - the pulses in a second option is good for high pulse rates input
and the period measurement technique is good for low pulse rate inputs.