Datex-Ohmeda F-LM1, Technical Reference Manual

Page: 155 / 377

Functional description
Red and infrared channel separation
Red and infrared channels are separated from each other by switches. Operational amplifier
functions as a buffer and after this infrared and red DC signals are sent to the processor. A
capacitor separates AC signal from DC signals and the AC signals are sent to the processor after
amplification. There is a switch to choose the amplification constant.
LED
dr
iv
ing
c
irc
uit
Am
pl
ifi
e
r
IR DC
le
ve
l
Re
d D
C
le
ve
l
Pr
ob
e
I=
5-
350m
A
Le
ve
l of
L
E
D
c
u
rr
en
t
m
e
a
su
rem
en
t an
d
fe
ed
ba
ck
c
irc
uit
Pr
ea
m
pli
fie
r
C
u
rr
e
n
t - t
o
- V
o
lta
g
e
co
n
ve
rt
e
r
Di
g
ita
lly
c
o
nt
ro
lle
d
at
tenu
at
o
r
IR
ed
L
E
D
in
te
n
si
ty
ad
ju
st
m
ent
Re
d L
E
D
in
te
ns
ity
ad
ju
st
m
ent
L
e
ve
l of
L
E
D
c
u
rren
t i
ndic
a
tion
(t
o
C
P
U
)
IR
ed A
C
si
gn
al
R
e
d A
C
si
gn
al
T
w
o st
ep
A
C
am
pl
ifier
G
=
18
o
r
12
5
G
=
18
o
r
12
5
G =
130
G =
A
WO
R
D
/4096
Figure 9 Pulse oximetry measurement block diagram
Document No. 8000060-1
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