Biomedical Engineering Reference
In-Depth Information
+Vcc
D1
1N4148
C3
10uF, 25V, tant.
+
-Vcc
+Vcc
C4 0.01uF
J2
1
3
Gain
R4
20K
C1
0.1uF
R3
100K, 1%
13
10
12
8
14
2
1
J1
R1
10M, 1%
+
1
2
4
5
J3
AC1 In
+In
11
7
2
IC1
1
Output
-In
R2
10 M, 1%
AC2 In
3
-
AD521JD
5
6
4
C2
0.1uF
Offset
R5
10K
C5
0.01uF
+
C6
10uF, 25V, tant.
D2
1N4148
-Vcc
Figure 2.5 This is a classic medium-impedance (10-MΩ) instrumentation biopotential amplifier based on the popular Analog Devices'
AD521 ICIA. The gain is adjustable between 10 and 1000 and maintains a CMR of at least 110 dB. The 40-kHz signal bandwidth makes
this front end suitable for recording EMG or ECG signals or as a general-purpose high-impedance ac-coupled transducer amplifier.
Supply voltage to the AD521 must be symmetrical and within the range
5 V (mini-
18 V (absolute maximum). D1 and D2 provide protection against incorrect sup-
ply voltage polarity, and capacitors C3-C6 are used to decouple and
mum) to
filter the power
supply. With a quiescent maximal supply current of 5 mA, a pair of 9-V alkaline batteries
constitute a suitable power supply for most applications.
To minimize electrical interference the circuit should be built with a compact layout on
an appropriate PCB or small piece of strip board. The construction of the circuit is straight-
forward, but care must be taken to keep wiring as short and clean as possible. Preferably,
leads to the bioelectrodes should be low-loss low-capacitance coaxial cables, whose
shields are connected to the subject ground terminal of the circuit. The construction of
systems incorporating this circuit is simple, but care must be taken to keep all wiring
as short and as clean as possible. When connected to a test subject, the circuit must always
fi
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