Assume that the OP_AMP in the figure, ideal

(a) Obtain an expression for V₀ in terms of V_s, R, and the reverse saturation current I_s of the transiostor.

(b) If R = 1$$\Omega $$, I_s = 1pA and the thermal voltage V_T = 25mV, then what is the value of the output voltage V₀ for an input voltage V_s = 1V?

(c) Suppose that the transistor in the feedback path is replaced by a p-n junction diode with a reverse saturation current of I_s. The p-side of the diode is connected to node A and the n-side to node B. Then what is the expression for V₀ in terms V_s, R and I_s ?

The current gain of a BJT is

An emitter-follower amplifier is shown in the figure, Z_i is the impedance looking into the base of the transistor and Z₀ is the impedance looking into the emitter of the transistor

(a)Draw the small signal equivalent circuit of the amplifier.
(b)Obtain an expression for z_i.
(c)Obtain an expression for z₀.

An npn BJT has g_m = 38 mA/V, $${C_\mu }\, = {10^{ - 14}}$$ F, $${C_\pi }\, = 4\, \times {10^{ - 13}}\,F$$ and DC current gain $$\beta \, = \,90$$. For this transistor f_T and $${f_\beta }$$ are