Exercise 4.4 An NPN amplifier and its PNP equivalent

a)

b)

An answer:
Both $V_{\mathit{DD}}$ and the capacitors are modelled by a short-circuit. Failing so most likely will force errors somewhere.

The derivation of $r_{\mathit{in}}$ is straight forward, leading to:

$$\begin{array}{rcll}{R}_{\mathit{in}}=R_3+R_1∕∕\frac{\mathit{\beta fe}}{g_m}& & & \end{array}$$

c)

d)

e)

f)