Patent ID: 7019719

Claim:
An apparatus for providing a reference voltage to a boost regulator that generates a drive voltage for a current source based on the reference voltage, the apparatus comprising: a first voltage source configured to generate a constant voltage; a second voltage source configured to generate a variable voltage; and a clamping circuit connected to each of the first and second voltage sources, and configured to generate the reference voltage based on the constant and variable voltages, said reference voltage being provided to the boost regulator at a level that is at least sufficient to cause the boost regulator to output a non-zero voltages, wherein the clamping circuit is configured to output as the reference voltage a greater one of the constant voltage and the variable voltage and wherein the clamping circuit comprises first and second components configured to receive the constant voltage and the variable voltage respectively, and third and fourth components configured to receive outputs of the first and second components respectively and to output the reference voltage to the boost regulator.