Patent ID: 7719348

Claim:
A filter device comprising: an operational amplifier, and a switched capacitor circuit coupled between an input and an output of the operational amplifier, the switched capacitor circuit comprising a first capacitor, a second capacitor, a third capacitor, and a switch arrangement, the switch arrangement being switchable during operation of the filter device with a constant switch frequency fclk so that the switched capacitor circuit is arranged to emulate a resistor during operation of the filter device, wherein the second capacitor has a capacitance value Cr which is determinable according to the formula: Cr=Cb /(1.1*( Cb*Rcr*fclk− 1)) wherein Rcr is a resistance value to be emulated by the switched capacitor circuit, fclk is the switch frequency and Cb is a capacitance value of the first capacitor comprised by the switch capacitor circuit.