A reference voltage generating circuit and method for tuning a reference voltage is described. A tunable current generator generates a tuned bias current for modifying each of a Proportional to Absolute Temperature (PTAT) voltage and Complementary to Absolute temperature (CTAT) voltage. A shift register is used to control tuning of the current by the tunable current generator. A voltage averaging circuit generates an average voltage by using the PTAT voltage and CTAT voltage so modified to generate an output reference voltage.