June
2005, Issue 179
Precision
Frequency Meter
Cypress
PSoC High Integration Challenge 2004 Contest Winner
MEASURING
FREQUENCY
A
common method for measuring frequency is to count the
number of cycles over a known time period (cycles/time).
This works well, but the sample time may be extremely
long if you need a precise measurement. For example,
measuring a frequency to 1 Hz requires you to sample
it for 1 s.
There’s
a better way. You can determine the frequency faster
if you accurately measure the period of a number of
input cycles. You’ll achieve accuracy if the reference
clock (the units that the period is measured in) is
a higher frequency than the input signal. For example,
with a 16-MHz reference clock, you can measure a 100-kHz
input signal to 0.006 Hz in 1 s. It would take 160 s
to obtain this level of accuracy by simply counting
cycles.
