PURPOSE: To set a cut-off frequency substantially over a wide range with low power consumption.
CONSTITUTION: In the active filter circuit employing a variable conductance circuit provided with a couple of input transistors(TRs) Q1, Q2 whose bases receive an input voltage signal respectively and whose emitters are provided respectively with a 1st constant current source I0, with a load means R1 provided to collectors of the input TRs respectively via a unidirectional conductive element, with differential TRs Q3, Q4 whose bases receive collector outputs of the input TRs Q1, Q2, with a 2nd variable current source I 1 connecting to the connecting point of emitters of the differential TRs Q3, Q4 in common, and with each current source load I2 connecting to collectors of the differential TRs respectively sharing each half of the current of the 2nd variable current source I1, the constant current value of the 1st constant current source I0 is changed to be smaller every time a frequency range gets higher.
NARA TAKASHI
WATANABE HISASHI
AKITA DENSHI KK