iq2 of the transistor q2 flow through the collectors of the transistors q6 q7 and q8 thus a current io flowing through the node n1 from the power source ass is given by the following expression where iq7 and iq11 are collector currents of the transistors q7 and q11 respectively by substituting expressions 1 and 2 for expression 3 the following expression is obtained equ2 by differentiating expression 4 with respect to vn1 a mutual conductance g in is derived as shown in the following expression equ3 in fig1 an input impedance r in1 when it is viewed from the node n1 toward the base of the transistor q1 is given by the following expression equ4 assume that the amplitude of the ac voltage signal v in is small and equ5 in this case an input impedance r ino is given by the following expression equ6 therefore when the amplitude of the ac voltage signal v in is small the current io which flows through the node n1 is given by the following expression equ7 on the other hand assuming that the current flowing through the resistor r2 is i1 and ac output voltage vo1 at the output terminal vo is given by.