A current generator includes an op-amp having a negative terminal arranged to be coupled to an input voltage, a resistance selection circuit having at least one tunable resistor connected with each other, and at least one power transistor. A gate of the at least one power transistor is coupled to an output of the op-amp, and a drain of the at least one power transistor is coupled to the at least one tunable resistor or a load. The resistance selection circuit is configured to select a node of the at least one tunable resistor based on the input voltage for coupling from a positive terminal of the op-amp. The at least one tunable resistor is configured to adjust a resistance setting to control a current level of the current generator based on a power supply voltage or a current of a reference resistor.