
84-6 Signal Processing
to v
in
(t) indicates the direction of imbalance. In sensors like these, the modulating signal f
m
(t) is physical
variable being measured. e use of ac excitation to a sensor is required for sensors containing reactive
elements (inductances and/or capacitances); it may also be desirable in the case of resistive sensors (such
as st
rain-gage
br
idges)
re
quiring
hi
gh-gain
am
pliers
. In th
ese
ci
rcumstances,
am
plication
of an ac
sig
nal
mi
nimizes
bo
th
1/f no
ise
an
d
dc
-oset
pr
oblems
as
sociated
wi
th
hi
gh-gain
dc
-coupled
am
pliers
.
84.3.3 Envelope Demodulation of DSB AM Signals
Full-carrier AM signals are readily demodulated by t