DESIGN AND DEVELOPMENT OF MEDICAL ELECTRONIC ...

48 BANDPASS SELECTION FOR BIOPOTENTIAL AMPLIFIERS+VccD1J2123-Vcc+VccC10.1uFR3100K, 1%1N4148C310uF, 25V, tant.+C40.01uFGainR420K13 108 142 12AC1 In+In-InAC2 InJ112345R110M, 1%R210M, 1%1113+-IC171 2J3OutputAD521JD564C20.1uFR510KOffsetC50.01uF+D21N4148C610uF, 25V, tant.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 makesthis front end suitable for recording EMG or ECG signals or as a general-purpose high-impedance ac-coupled transducer amplifier.-VccSupply voltage to the AD521 must be symmetrical and within the range 5 V (minimum)to 18 V (absolute maximum). D1 and D2 provide protection against incorrect supplyvoltage polarity, and capacitors C3–C6 are used to decouple and filter the powersupply. With a quiescent maximal supply current of 5 mA, a pair of 9-V alkaline batteriesconstitute a suitable power supply for most applications.To minimize electrical interference the circuit should be built with a compact layout onan appropriate PCB or small piece of strip board. The construction of the circuit is straightforward,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, whoseshields are connected to the subject ground terminal of the circuit. The construction ofsystems incorporating this circuit is simple, but care must be taken to keep all wiringas short and as clean as possible. When connected to a test subject, the circuit must always