where formula_96 is the device width, formula_97 is its length and formula_98 the device threshold voltage. Random lithographic variations are reflected as different values of the formula_99 ratio of each transistor. Similarly threshold variations appear as small differences in the value of formula_98 for each transistor. Let formula_101 and formula_102. The mirror circuit of Fig. 5 forces the drain current of M1 to equal the input current and the output configuration assures that the output current equals the drain current of M2. Expanding equation (8) in a two-variable Taylor series about formula_103 and truncating after the first linear term, leads to an expression for the mismatch of the drain currents of M1 and M2 as: