Charge routing network (CRN) denotes a family of particular functional electronic devices offering the possibility of achieving discrete-time signal processing. A \(p\)-phase CRN consists of storage cells divided into \(p\) subgroups and a routing procedure controlled by a \(p\)-phase clock. During a particular clock phase, charge is routed from a particular subgroups of storage cells into another group. It allows a wide range of electronic functions. They are often analog and CRN offers the possibility of sampled-data filtering functions. The class of filters attainable using CRN's was not known up to now, nor was a systematic procedure available to obtain a graph of a CRN from a given allowable transfer function. CRN can be completely described by a digraph. CRN 's modus operandi is first given and their input-output relation is derived. A necessary and sufficent condition determining the class of filters realizable as a \(p\)-phase CRN is proved. A numerical example is supplied.