Welch Allyn Atlas Service Manual page 89

Wilson
Network
RA
R529 10K
R530 10K
LA
R531 10K
R532 10K
LL
R533 10K
R534 10K
V+
R535 10K
R536 10K
R537 10K
2.5.5 Differential Amplifier and Slew rate limit
A traditional 3-opamp gain stage (U507 and U508) is used to construct the differential amplifier. The
topology is modified slightly with the addition of slew rate limiting (U509). The ECG signal is slew rate
limited to about 100V/sec. This is done to minimize distortion of the ECG trace in the presence or large
pace pulses. The differential outputs of this stage are used as input to the RLD amplifier.
fVcc
3
mux- +
diff-
1
2
-
U507A
MC34002
fVee
fVcc
5
mux+
+
7 diff+
6
-
U507B
MC34002
fVee
2.5.6 Right Leg Drive Amplifier
The right leg amplifier performs two functions. First is to provide bias current to the input buffer
amplifiers. Second, to reduce 60Hz interference (increase CMR). Patient Common mode signals are
amplified and inverted, and this resultant signal used to drive the patient. Gain of the RLD amplifier at
60Hz is maximized, while keeping the system gain stable. The RLD output is mux'd to the appropriate
wire depending on the chosen input vector. For example, when looking at Lead I (LA-RA), the RLD
signal is switched to the LL buffer.
Appendix A
Lead Select
fVcc
U505
4051
RA
13
X0 X
RA
14
X1
LA
15
X2
aVR 12
X3
aVL 1
X4
aVF
5
X5
V- 2
X6
4
X7
6
INH
11
A
10
E
B
9
C
VEE
E
fVcc
U506
4051
LA
13
X0 X
14
X1
LL
15
X2
RA
12
X3
LA
1
X4
LL
5
X5
V+ 2
X6
4
X7
6
INH
11
A
10
B
9
E
C
VEE
E
Diff Amp and Slew Rate Limit
DC Gain = 1
C544
1000pF
R544 R546
10K 0.1% 10K
U508-3
fVcc
R545 3
+
10K 0.1% 1
2
-
U508A
AD712
C542
fVee 220pF
u508-2
R547
10K
0.1% C545
1000pF
E E
3 mux-
7
fVee
3 mux+
7
fVee
0.1%
C543
.047uF
fVcc
R565
121K
4
-
1
3
+
U509
LMC7101
E
fVee
10/14/99
SingEnd Out