| 摘要 |
PURPOSE:To change the value of fO and/or Q of an active filter, by changing capacitance ratio of two capacitors alpha, resistance ratio of two capacitors (m), and a gain K of an amplifier being the active element with a switching circuit. CONSTITUTION:When a switch 17 is disconnected and a capacitor C3 does not give any effect on the characteristics, a cut-off frequency fO1 and a Q which show the characteristics of a 2nd order low pass filter have the relation of fO1=1/2piR1C1.(alpham)<1/2> and Q1=(malpha)<1/2>/malpha+ (1-K)+alpha. When the switch 17 is closed, since C'2 is C2+C3, the fO and the Q are expressed in the following equation: fO2=1/2piR1C1.(alpha'm);Q2=(malpha')<1/2>/malpha'+ (1-K)+alpha', where K is the gain of the amplifier and C2'=alpha'C1. Thus, two types of low pass filters having the specified fO and Q can be constituted through the connection/disconnection of the C3. |
