1. A circuit, comprising: a current summing junction; a bandgap current source circuit configured to generate a bandgap current applied to the current summing junction, wherein a magnitude the bandgap current is constant for a supply voltage which exceeds a first voltage threshold; and a variable current source circuit configured to generate a variable current applied to the current summing junction, wherein a magnitude of the variable current varies dependent on change in the supply voltage; wherein the variable current is offset against the bandgap current at the current summing junction.