Active bandpass filter principle

Second order band-pass filter performance depends primarily on the quality factor Q and center frequency Si. In order to adjust the Q and. t a general first adjust R3 to change the Q value, and then adjust to change C 0. But the adjustment will affect R3 Si.

Figure R4 and Si-independent, so that the capacitor C is now open, according to the same phase-inverting terminal of the operational amplifier to ground the DC resistance of the principles of equality, availability R4 = R3 = R3. Second order bandpass filter the Q value of the maximum undeclared more than 20, and generally 10 is appropriate, Q values of the election was high, resistance is 2 feet lower bound value, so the input signal will be severely attenuated, and to increase the amplifier burden. Since the Q value of the parameter element number of errors is very sensitive in general to 0 10 appropriate. KF is the maximum transmission ratio can range from 1 ^ f100 select within, if the display driver stage amplifier with an adjustable gain, the band-pass filter 10 to take appropriate din KF. In determining the value of Q, fo KF and after, can be obtained in the filter R l, R R 3, C and R4 of value.

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