<s>
Pulse-frequency	B-Device
modulation	I-Device
(	O
PFM	O
)	O
is	O
a	O
modulation	B-Application
method	O
for	O
representing	O
an	O
analog	O
signal	O
using	O
only	O
two	O
levels	O
(	O
1	O
and	O
0	O
)	O
.	O
</s>
<s>
It	O
is	O
analogous	O
to	O
pulse-width	B-Algorithm
modulation	I-Algorithm
(	O
PWM	O
)	O
,	O
in	O
which	O
the	O
magnitude	O
of	O
an	O
analog	O
signal	O
is	O
encoded	O
in	O
the	O
duty	O
cycle	O
of	O
a	O
square	O
wave	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
the	O
frequency	O
of	O
the	O
pulse	O
train	O
is	O
varied	O
in	O
accordance	O
with	O
the	O
instantaneous	O
amplitude	O
of	O
the	O
modulating	B-Application
signal	I-Application
at	O
sampling	O
intervals	O
.	O
</s>
