Q:     Determine the value of the diode small signal resistance r_d at bias current of 0.1,1 & 10mA.                              

Suppose  n =1

SOLUTION:

                                                            r_d = n V_T/ I

                                                            here V_T =25m Volt

                                                                            = 1 x25m   //putting the value

                                            for      I = 1mA,        r_d = 25ohms

                                                        I = 0.1mA,    r_d = 250ohms

                                                    I = 10mA,      r_d = 2.5ohms