STATE_VARIABLE_DESIGN

Published:2009/7/2 8:38:00 Author:May | From:SeekIC

Universal filter network using three opamps can provide low-pass, high-pass, or bandpass audio response for CW and SSB reception. Filter uses one summing block U1, two identical integrators, U2 and U3, and one damping network. Cutoff frequencies are same as center frequency for bandpass response. Article gives design equations and graph for choosing values to give optimum performance for type of response desired, For unity-gain second-order Butterworth filter with low-pass or high-pass cutoff of 700 Hz, R is 6800 ohms and C is 0.033 μF. Q must be fixed at 0.707 and RA must equal 1.12 × RB. Thus, if RB is 2700 ohms, RA should be 3OOO.-H. M. Berlin, The State-Variable Filter, QST, April 1978, p 14-16.



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