Biomedical Engineering Reference
In-Depth Information
R0
+
R1
R2
T1
C0
+
R2
C1
C2
C2
R1
C2
C3
C1
R3
R2
R0
+
+
T1
C0
R4
Fig. 3.6 Filtering for noise reduction. a Band-pass filtering. b Twin-T notch filter for 50-Hz
noise reduction
3. Filtering: Filtering at the first stage of the amplifier can greatly reduce the
unwanted interference. This is shown in Fig.
3.6
. Small inductors and ferrite
beads (indicated as T1) in the lead wires help to block high-frequency elec-
tromagnetic interference. C0 and R0 connected at the lead wire reduce radio
frequency interference [
13
].
Additionally, the C1 and R1 constitute a high-pass filter and C2 and R2 the low-
pass filter, with an effective bandpass given as
f
C
¼
1
2p
1
R
1
C
1
1
R
2
C
2
ð
3
:
6
Þ
For power line frequency rejection, an adjustable quality twin-T notch filter is
used where the tuning frequency is given as
1
2pR
1
C
1
f
0
¼
ð
3
:
7
Þ
where R
1
= R
2
= 2R
3
; C
1
= C
2
= C
3
/2.
3.4 A Single-Channel ECG Acquisition System
As mentioned in
Sect. 3.2
, the trend is to use customized DAS cards and appli-
cation software in ECG acquisition systems in clinical setup. The immediate
advantages are as follows: easy data storage and retrieval, data sharing in digital
format, and computerized analysis. In this section, a stand-alone DAS card
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