There is described a continuous time filter of at least a second (or higher) order, comprising: one or more first-order filter stages of a first type (100), the or each first-order filter stage (100) of the first type comprising a reactive component and an impedance (101; 102) dependent on the difference between the input and output voltages of the filter stage; at least one first order filter stage of a second type (120), the or each second order filter of the second type (120) comprising a reactive component and an impedance (91; 92) dependent on the sum of the input and output voltages of the filter stage; wherein a transfer function of the continuous time filter is obtained comprising complex poles.
