1. A circuit for generating a constant current, comprising: a first current generator that conducts a first current based upon a supply voltage and a resistive element; a second current generator that generates a second current based on the first current wherein the second current decreases as the first current increases and increases as the first current decreases; a summing circuit for summing currents proportional to said first and second currents to generate an output current, wherein the summing circuit comprises: a first current mirror for providing a first mirrored current proportional to the first current; a second current mirror for providing a second mirrored current proportional to the second current; and a summing device for summing the first and second mirrored currents to provide a first reference current, and a third current mirror for providing a second reference current proportional to the first reference current.