
18-21Meter Voltage Measurement
e modulator operating principle is shown, in the time domain, in Figure 18.21. Let us suppose that
th
e
in
put
vo
ltage
V
in
is positive and constant and the integrator output is negative at the rst clock pulse.
Con
sequently,
th
e
co
mparator
ou
tput
V
bs
is switched to the low level by the clock pulse. e DAC output
vo
ltage
is sw
itched
to th
e
ne
gative
−V
DA
value and subtracted to V
in
, so that the input signal ε to the integrator
is po
sitive
an
d
hig
h
en
ough
to fo
rce
th
e
in
tegrator
ou
tput
V
c
to become positive before the next clock pulse.
Co
nsequently,
th
e
co
mparator
ou
tput
is sw
itched
to th
e
hi
gh
va
lue
at th
e
ne
xt
cl