Vec R: lo Q Figure 13.15 A bipolar two-stage op amp with class AB output stage. The input common-mode range is limited by the input differential pair with current-mirror load, and the output swing is limited by the class AB output stage/nSedra Chapter 13 *13.44 The resistors R₁ in Fig. 13.15 are mismatched so that one has a value R₁ + AR₁. You may assume that the base currents are negligible. (a) Show that this results in mismatched emitter currents in Q and Q ΔΙ AR₁ R₁ + AR, +r, (b) Show that this, in turn, results in an input offset voltage of Vos AR,VT R₁+ AR, +r, (c) If an input offset voltage of Vos is observed, show that this can be compensated for (ie., reduced to zero) by creating a relative mismatch in the resistors R₁. AR = Vos 1+r/R, R₁ V, 1-Vos/V

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