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4 Measurement of Biosignals and Analog Signal Processing

OPV2

LT1179

OPV1

LT1179

OPV3

LT1179

R1

22k

R2

22k

R3

220

R4

22k

R6

22k

R7

22k

Rü1

2k

Rü2

2k

Ugl

Uekg

R8

2k

R9

200k

R10

200k

22k

470k

+15V

+15V

+15V

-15V

-15V

-15V

Ue1

Ue2

Ua1

Ua2

Fig. 4.9: Potentiometer circuit for adjusting R5/R4 = R7/R6 in the instrumentation amplifier accord-

ing to Figure 4.8: The potentiometer circuit replaces resistor R5 in Figure 4.8.

Fig. 4.10: Extension of the instrument amplifier from Figure 4.7 by a further amplifier stage as well as

a high-pass and two low-pass filters.

The circuit from Figure 4.7 is now supplemented with regard to the previously de-

scribed requirements. A further amplifier as well as a high-pass and two low-pass fil-

ters are connected downstream. Figure 4.10 shows the extended circuit.

OPV4 together with R9,10 forms a non-inverting amplifierwithgain5.5.This givesa

total gain of 1100 for both amplifier stages. C1 and R8 form a high-pass filter with cutoff

frequency 0.16 Hz. The first low-pass filter is realized by the capacitors C3,4. At high

signal frequency, the parallel resistors R5,7 are almost short-circuited by C3,4, whereby

the gain of the subtractor falls far below one. The cutoff frequency is approximately

3.3 kHz. The second low-pass filter is produced by the capacitor C2 in parallel with R9,