A2. Design procedure for high pass filter
Define the cut-off frequency Fc = 0.5 Hz
Choose C capacitor value, since C = C1 = C2, we proposed C = 0.47μF. The capacitor choice was in terms of lower cost and greater feasibility of achieving better performance with respect to the frequencies at which it worked.
Calculate the value of the resistor R1 and R2 by the equation
=0.95 MΩ
=0.475 MΩ
To establish R3 resistance that is connected to the operational output and capacitors (R3):
R3 =R1/2 = 0.95 /2 = 0.475 MΩ
Figure 8. High pass Filter circuit
Pre Amplifier (i) & (ii)
The Amplifier ensures that adequate signal is passed to the next block.
Gain: = 1+ = 1+ = 2
Reference resistor = 1.1kΩ (1 kΩ)
Figure 9. Preamplifier Circuit
Instrumentation Amplifier
The instrumentation amplifier used is Analog Devices iAD620. Analog devices AD620 data sheet specifies gain up to 10000. However, it is found that for a gain of 991, RG =49.9 Ohms is required. Most suitably gain can be up to 1000 since higher gains will require RG value very low. We have selected a gain of 100 with RG= 499Ω (510Ω).
G = 1 + (49.4 kΩ/RG)
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