ACTIVE ELECTRONIC FILTER CIRCUIT

摘要

PROBLEM TO BE SOLVED: To provide high impedance by highly accurately preparing it within a small semiconductor area on the main body of semiconductor by forming a T circuit network by providing an input impedance device with plural impedance branches. SOLUTION: The input impedance device is provided with the T circuit network having five impedance branches 21-25. The first branch 21 has one end connected to a first filter input terminal 8 and the other end connected to a first branch point 12. The third branch 23 is arranged between the first branch point 12 and a non-inverted amplifier input terminal 2. The second branch 22 is arranged between a second filter input terminal 9 and a second branch point 13, and the second branch point 13 is connected through the fourth branch 24 to an inverted amplifier input terminal 3. The fifth branch 25 is arranged between two branch points 12 and 13. Then, one part of signal currents flowing through the filter input terminals 8 and 9 surely avoids the practical zero point of an amplifier element 1.