
q is electron charge
k is Boltzmann's constant
T is absolute temperature.
Then,v_i at the input equals
(a)-RI_S(e^{[qv_o/kT]} -1)
(b)-RI_S(e^{[-qv_o/kT]} +1)
(c)R/I_S(e^{[qv_o/kT]})
(d)insufficient data,cannot be determined
Answer is (a)
The voltage at inverting input can be neglected such that the output voltage equals the diode voltage.Under this condition, i_D and i_R sum to zero i.e., i_D + i_R = 0 ,\implies i_R=-i_D
i_R = v_i/R, \implies v_i = -Ri_D
\therefore v_i = -RI_S(e^{[qv_D/kT]} -1)