Patent ID: 6838929

Claim:
An integrated circuit arrangement with an active filter comprising transconductance stages (gm 1 , gm 2 , gm 3 , gm 4 ), each being adjustable by means of a bias current (Itun) to be supplied, and comprising a tuning device for tuning the filter, which tuning device adjusts the bias currents of the transconductance stages, wherein the tuning device adjusts the bias current (Itun 1 ) of a first (gm 1 ) transconductance stage, for the purpose of achieving a desired characteristic of this transconductance stage, and adjusts the bias current (0.8*Itun 1 +Itun 2 ) of at least one further (gm 2 ) transconductance stage such that the transconductance (gm 2 ) of this further transconductance stage deviates from the transconductance (gm 1 ) of the first transconductance stage by a value (2*gds) which corresponds to the sum of output admittance values (gds+gds), each of which output admittance values subject an output of the transconductance stages (gm 1 , gm 2 , gm 3 , gm 4 ) to a load, wherein the bias current (0.8*Itun 1 +Itun 2 ), which for this purpose is to be supplied by the tuning device to the further transconductance stage (gm 2 ), is defined at a closed-loop control circuit, wherein the closed-loop control circuit comprises: an arrangement of replicas of at least the first transconductance stage (gm 1 ) and of the further transconductance stage (gm 2 ); current sources for supplying the first bias current (Itun 1 ) to the replica of the first transconductance stage and a regulated further bias current (0.8*Itun 1 +Itun 2 ) to the replica of the further transconductance stage; a voltage source for applying an input voltage (Uref) to an input of the arrangement; and a comparator for comparing an output voltage (Uout) of the arrangement with the input voltage (Uref) and for providing a comparison signal which is supplied as a control signal to the current source of the replica of the further transconductance stage (gm 2 ), in order to adjust the further bias current (0.8*Itun 1 +Itun 2 ) such that the output voltage (Uout) becomes equal to the input voltage (Uref); so that the further bias current (0.8*Itun 1 +Itun 2 ) defines the current to be supplied by the tuning circuit to the further transconductance stage (gm 2 ).