An apparatus includes a first voltage reference circuit, a second voltage reference circuit and a third circuit that is coupled to the second voltage reference circuit. The first voltage reference circuit provides a first reference voltage between a terminal of the first voltage reference circuit and a first power line. The second voltage reference circuit provides a second reference voltage between a terminal of the second voltage reference circuit and a second power line that is separate from the first power line. The third circuit is coupled to the second voltage reference circuit to establish a magnitude of the second reference voltage in response to a potential difference between the terminal of the first voltage reference circuit and the second power line.