Charge pump bias network

A circuit for supplying selected currents to a charge pump without harmful effects arising from operation of current switches in the charge pump. A charge pump current setting is applied in digital form to a set of two-position switches coupled to binary-weighted current sources. Currents from the sources selected by the switches are combined, and the total current is mirrored to the charge pump. Simultaneously, those of the binary-weighted current sources not selected by the switches to contribute to the charge pump current are separately combined, and this total current is mirrored to an electrical replica of the charge pump. Thus the currents supplied to the charge pump and to the replica charge pump are complementary in the sense that they always add to a constant total current drawn from a common power supply. Therefore, abrupt changes in current load are avoided and switching noise effects are minimized.