A current monitoring circuit capable of being integrated onto an integrated circuit chip with the current source to be monitored, wherein the monitored current is digitized to be transmitted within and external to the host integrated circuit chip. The current monitoring circuit was originally conceived to monitor output current of a buck switching regulator but can be used in other applications. A replica transistor is drain connected to a replicated transistor, wherein an operational transconductor controls the replica transistor to produce the same current that flows in the replicated transistor and connects a copy of the current of the replicated transistor current to an integrating type ADC.