Electrical Engineering ⇒ Topic : Input resistance RiF of Practical inverting op Amp

Input resistance RiF

Referring to Figure (a) and using the approximations V'_s = V_s and R'₁ = R₁, the current I through the loop with R_L = ∞ is given by

                                                              figure (a)

                                              ............. (1)

And also from Figure 1 (a), it can be written as:

                                V_i = V_s - IR₁                                    ............... (2)

Substituting Eq. (2) into Eq. (1), we have

                                  ............... (3)

Since A, is very large,the second term in Eq. (29.34) will be very low and R₁ decides R_iF

Input resistance RiF

Referring to Figure (a) and using the approximations V'_s = V_s and R'₁ = R₁, the current I through the loop with R_L = ∞ is given by

                                                              figure (a)

                                              ............. (1)

And also from Figure 1 (a), it can be written as:

                                V_i = V_s - IR₁                                    ............... (2)

Substituting Eq. (2) into Eq. (1), we have

                                  ............... (3)

Since A, is very large,the second term in Eq. (29.34) will be very low and R₁ decides R_iF