The REF20xx are a family of dual-output, V_REF and V_BIAS (V_REF / 2) band-gap voltage references. The Section 9.2 section provides a block diagram of the basic band-gap topology and the two buffers used to derive the V_REF and V_BIAS outputs. Transistors Q₁ and Q₂ are biased such that the current density of Q₁ is greater than that of Q₂. The difference of the two base emitter voltages (V_BE1 – V_BE2) has a positive temperature coefficient and is forced across resistor R₅. The voltage is amplified and added to the base emitter voltage of Q₂, which has a negative temperature coefficient. The resulting band-gap output voltage is almost independent of temperature. Two independent buffers are used to generate V_REF and V_BIAS from the band-gap voltage. The resistors R₁, R₂ and R₃, R₄ are sized such that V_BIAS = V_REF / 2.

e-Trim™ is a method of package-level trim for the initial accuracy and temperature coefficient of V_REF and V_BIAS, implemented during the final steps of manufacturing after the plastic molding process. This method minimizes the influence of inherent transistor mismatch, as well as errors induced during package molding. e-Trim is implemented in the REF20xx to minimize the temperature drift and maximize the initial accuracy of both the V_REF and V_BIAS outputs.