Exercise 5.11 An NPN amplifier

Given is the circuit below. For the BJT, the active forward region of operation may be assumed. In this region of operation, $i_C=I_{C0}\cdot e^{\frac{q\cdot v_{\mathit{BE}}}{\mathit{kT}}}$; the $\mathit{\beta fe}$ is finite and cannot be neglected. At signal frequencies, the capacitors can be assumed to be low-impedant and the inductors can be assumed to be high-impedant.

a)

derive a small signal equivalent circuit.

b)

derive an expression for the output impedance $z_{\mathit{out}}$.

c)

derive an equation for the required value of resistor $R_1$ to get a collector bias current equal to $I_C$, as a function of all relevant component values/properties.

d)

derive an expression for the input impedance $z_{\mathit{in}}$ as seen by the signal source.

e)

derive an expression for the voltage gain $a_v=v_{\mathit{out}}∕v_{\mathit{in}}$.

f)

derive a small signal equivalent for the transistor in the circuit assuming a slightly different element equation than used in the previous questions: $i_C=I_{C0}\cdot e^{\frac{q\cdot v_{\mathit{BE}}}{\mathit{kT}}}\cdot (1+\lambda \cdot v_{\mathit{CE}})$. The transistor’s current gain $\mathit{\beta fe}$ is finite and cannot be neglected. ALSO derive (not: only state) the small signal parameters as function of e.g. the bias current $I_C$ of the transistor. Physics constants are constant and the temperature T may be assumed to be constant.