A start-up circuit includes a long channel current generator, a subtracting reference current generator, and a gain scaling current mirror-circuit. The long channel current generator circuit uses a long channel transistor circuit that simulates a high value resistor to provide a low-level current. The low-level current is sensed by the subtracting reference current generator to provide a reference current that tracks the low-level current until a diverting current is activated, where the diverting current is subtracted from the reference current such that the reference current increases at a slower rate than the low-level current for increasing supply voltages. The gain scaling current mirror-circuit generates the start-up current as a gain scaled version of the reference current. Once the bias generator circuit is active, a stop-current can be used to shut down the gain scaling current mirror-circuit to conserve current.