$14\mathrm{.}57.$ The push$-$pull stage of Fig. $14\mathrm{.}15($b$)$ must

be designed for an output power of

$2$ W and R$\_($L$)=8\backslash$Omega $.$ Assume $|$V$\_($BE$)|$~~$0\mathrm{.}8$V$,$

$\backslash$beta $\_(1)=40,$ and $\backslash$beta $\_(2)=20.$

$($a$)$ Determine the minimum required

supply voltage if Q$\_(3)$ and Q$\_(4)$ must re$-$

main in the active region.

$($b$)$ Calculate the minimum required bias

current of Q$\_(3)$ and Q$\_(4).$

$($c$)$ Determine the average power dissi$-$

pated in Q$\_(1)$ while the circuit delivers

$2$ W to the load.

$($d$)$ Compute the overall efficiency of the

circuit, taking into account the bias

current of Q$\_(3)$ and Q$\_(4).($b$)$