Method and circuit for curvature correction in bandgap references with asymmetric curvature

Abstract

A non-linear correction current ICTAT(current complementary to the square of absolute temperature) is generated from a current IPTAT (current proportional to absolute temperature) and a current ICTAT (current complementary to absolute temperature), both modified in a circuit having a topology and components which capitalize on the logarithmic relationship between transistor collector current and base-emitter voltage. The resulting ICTATcurrent (current complementary to the square of absolute temperature) is injected into a node of a bandgap reference circuit to compensate for non-linear temperature effects on output voltage. A more general correction circuit generates both IPTATand ICTAT, and applies each to a respective multiplier which, in a preferred embodiment, is a current DAC configured as a multiplier. Control inputs CTLand CTLto respective multipliers set the amplitudes of the modified IPTATand ICTAToutput currents, which are then summed to generate the compensating current Icomp which is injected to the appropriate node in the bandgap reference circuit as described above. By adjusting the relative amplitudes of the IPTATand ICTATcurrents, a wide range of compensating current versus voltage curves is produced, allowing the optimization of a wide range of bandgap reference circuits. An optimal value for CTLis determined by holding CTLconstant, then measuring curvature at a plurality of CTLvalues. That CTLvalue closest to the interpolated value at which curvature is minimized is then used.