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DESIGN AND DEVELOPMENT OF MEDICAL ELECTRONIC ...

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INVERTING INPUTD2BZD27C11D4BZD27C11NON-INVERTING INPUTC214.7nFR547kD3HSMS2802R947k231R647kC22470pFR1047k5V_ISOC20100nF2.5V_ISOIIR7360R8100kC231uFC24220nFC30560nFC2547nFC31100nFC3222nFC2610nFC274.7nFA6 A7A5 A8A4 A9A3 A10A2 A11A1 A12C28R4 1MI2.2nF2374 8-+327 1+-4 8 5IC5INA128U665V_ISOC29100nFISW1ASW ROTARY 2P-12WIC4UPC4250G2LOW PASS 1Hz 1LOW PASS 2Hz 1LOW PASS 5Hz 1LOW PASS 10Hz 1LOW PASS 20Hz 1LOW PASS 50Hz 1LOW PASS 100Hz 1LOW PASS 200Hz 1LOW PASS 500Hz 1AIB1 B2 B B12B11B3 B4 B5 B10B9B8B6 B7LOW-PASS FREQ.CUT-<strong>OF</strong>F SELECTIONSW1BSW ROTARY 2P-12WC33 C36 C34 C37 C35 C38 C39 C41 C401uF 560nF 220nF 100nF 47nF 22nF 10nF 4.7nF 2.2NFR121 MSW2First Order (Open) / Second Order (Closed) SelectorR11100kI234 8-+6IC6UPC4250G2LOW PASS OUT75V_ISOIC42100nFFigure 2.7 In this biopotential amplifier, biopotentials are amplified by a Burr-Brown INA128U instrumentation amplifier. R5, R6, R9,R10, and C22 implement a low-pass filter with a cutoff of approximately 3.6 kHz. The biopotential amplifier’s main low-pass filters areimplemented by two cascaded RC passive filters with selectable cutoff frequency. IC4 buffers the signals between the cascaded sections. Thetwo RC sections are identical, therefore setting a pole at the same frequency. However, the effect of the second RC can be suppressed by disconnectingits capacitor through switch SW2.51

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