Active high-pass filter and an active low-pass filter

摘要

PURPOSE:To obtain an active high pass filter capable of switching a frequency characteristic to a secondary filter characteristic and a flat characteristic by a simple constitution. CONSTITUTION:In a Butterworth secondary active high-pass filter, a first switching element Q1 is inserted in a feedback loop 5 of an amplifier 3 and a resistance value of a resistor composing a time constant circuit 6 is switched to a normal resistance value R2 and resistance values R2+R3 which are much greater than this by a second switching element Q2. The feedback loop of an amplifier 3 is closed, the resistance value of the resistor composing the time constant circuit 6 is switched to the normal value R2 and a frequency characteristic is made a secondary active high-pass filter characteristic. The feedback group 5 of the amplifier 3 is opened, the resistance value of the resistor composing the time constant circuit 6 is switched to the resistance values R2+R3 which are much greater than the normal resistance value and the frequency characteristic is made a flat characteristic.