An apparatus and method for producing an output reference voltage is
provided. A voltage divider is configured to provide the output reference
voltage from a bandgap reference voltage. The bandgap reference voltage
is applied across a biased portion of the voltage divider. Additionally,
a second-order temperature coefficient (TC) of the impedance of a
controllable portion of the voltage divider is adjusted in response to a
second-order trim signal. The first and zeroth order TCs of the
controllable portion of the voltage divider are substantially independent
of the second-order trim signal. In one embodiment, the controllable
portion includes a resistor digital-to-analog converter (DAC) that is
responsive to the second-order trim signal. The resistor DAC includes at
least two different types of resistors. The second-order TCs of the two
different types of resistors are substantially different.