PURPOSE: To prevent an increase of voltage for the output of each integrator, by using a capacitor having a constant transmission function of an equivalent leapfrog type active filter and decided with different resistance values for an LC simulation- type switched capacitor filter which is suited for an LSI formation.
CONSTITUTION: A switched capacitor filter SCF2 is formed by replacing the resistance of an integrator in a leapfrog type active filter 1 which functions as an equivalent circuit in an LC filter circuit with a capacitor C and a switch SW. The 1st integrator consists of an operational amplifier AMP1, resistances R1∼R3 plus a capacitor C1; the 2nd integrator consists of an operational amplifier AMP2, resistances R4 and R5 plus a capacitor C3; and the 3rd integrator consists of an operational amplifier AMP3, resistances R6 and R7 plus a capacitor C4 respectively. In such constitution, the condition under which the transmission function is constant between the input and output is obtained along with the value with which R1, R2 and R7 are 1 and R3∼R6 are not 1. Thus an increase of voltage is prevented for the output of an integrator. Then an SCF is constituted with a switch having a capacitor value equivalent to the resistance plus a switch frequency.
KOMAZAKI TOMOKAZU
KOMORI ATSUSHI
KOZUKA SEIICHIROU
TSUBOI TOSHINORI
NIPPON TELEGRAPH & TELEPHONE