A current source including a current mirror circuit and an active load circuit which form a reference branch, for setting a reference current value, and a mirroring branch, defining an output current value, connected between supply and ground. A voltage stabilizing transistor is interposed between the current mirror circuit and the load circuit in the reference branch only, and is so biased as to maintain its gate terminal at a predetermined voltage. As such, the potential with respect to ground of the drain terminal of the reference branch load transistor is fixed, so that its drain-source voltage drop (and the current through it) is substantially independent of supply voltage. The current source may be used to advantage in an oscillator for generating the: clock signal of a nonvolatile memory.