Patent ID: 7038531

Claim:
An active filter comprising: a main operational amplifier ( 100 ) having an inverting input ( 100 a ), a noninverting input ( 100 b ) and an output ( 100 c ); a capacitor ( 101 ) having one end ( 101 a ) connected with the output ( 100 c ) of said main operational amplifier ( 100 ), and a second end ( 101 b ) connected with the inverting input ( 100 a ) of said main operational amplifier ( 100 ); a resistor ( 102 ) having one end ( 102 a ) connected with the inverting input ( 100 a ) of said main operational amplifier ( 100 ) and a second end ( 102 b ) defining an input of said filter ( 1 ); a secondary operational amplifier ( 110 ) having an inverting input ( 110 a ), a noninverting input ( 110 b ) and an output ( 110 c ), at least one of said outputs ( 100 c , 110 c ) being an output of said filter ( 1 ); feedback means ( 120 ) connected between the output ( 110 c ) of said secondary operational amplifier ( 110 ) and the inverting input ( 110 a ) of said secondary operational amplifier ( 110 ); a resistor ( 130 ) having one end ( 130 a ) connected with the inverting input ( 110 a ) of said secondary operational amplifier ( 110 ) and a second end ( 130 b ) connected with the output ( 100 c ) of said main operational amplifier ( 100 ), wherein the noninverting input ( 100 b ) of said main operational amplifier ( 100 ) is connected with the inverting input ( 110 a ) of said secondary operational amplifier ( 110 ).