low noise bandgap voltage references using a cascaded sum of bipolar transistor cross coupled loops . these loops are designed to provide the total ptat voltage necessary for one and two bandgap voltage references . the ptat voltage noise is the square root of the sum of the squares of the noise voltage of each transistor in the loops . the total noise of the reference can be much lower than approaches using two or 4 bipolar devices to get a ptat voltage and then gaining this ptat voltage to the required total ptat voltage . the cross coupled loops also reject noise in the current that bias them . alternate embodiments are disclosed .