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Help me understand band pass design in PIR sensor

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ericyeoh

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Guys i still dun understand the band pass design in below attrached circuit.

the 1st IC1A and IC1B opamp hv , FL and FH at 1.59hz.

FH = (1/[2(pie) 10mic x 10K]) = 1.59hz
FL = (1/[2(pie) 0.1mic x 1M]) = 1.59hz

how come both cut off frequency at 1.59hz? if this is the case, the bandwidth =0 hz?

Please help me pls, i'm lost
 

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Re: PIR sensor need help

Your calculations are correct but that doesn't mean you will have zero bandwidth. The cut off frequencies are where the signal has dropped by 3dB. So, the peak response will be around 1.6Hz and it will roll off on either side.

Keith.
 
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