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.

For the amplifier of given figure,
$${I_C}\, = \,1.3\,mA,\,{R_C}\, = \,2\,k\Omega ,\,{R_E}\, = \,500\,\Omega ,$$
$${V_T}\, = \,26\,mV,\,\beta \, = \,100,\,{V_{CC}}\, = \,15V,$$
$${V_s}\, = \,0.01\,\sin \left( {\omega t} \right)\,V\,and\,{C_b}\, = \,{C_C}\, = \,10\,\mu F.$$

(a)What is the small-signal voltage gain, $${A_V} = {V_0}/{V_s}?$$
(b)What is the approximate $${A_{v,}}\,\,if\,\,{C_e}\,\,$$ is removed?
(c)What will $${V_0}\,be\,if\,{C_b}$$ is short circuited?

A bipolar junction transistor amplifier circuit is shown in the figure. Assume that the current source I_bias is ideal, and the transistor has very large$$\beta ,\,\,{r_{b\,\,}} = \,\,0,$$ and the $${r_0}\, \to \,\infty $$.

Determine the ac small-signal mid-band and voltage gain $$\left( {{V_o}/{V_s}} \right),$$ input resistance (R₁, and output resistance (R₀) of the circuit. Assume $${V_{T\,\,}} = \,\,26\,mV.$$

In the circuit of fig. Determine the resistance R_o seen by the output terminals, ignore the effects of R₁ and R₂.