$(40$ pts$)6.$ A B$.$JT Negative Impedance Circuit

The following circuit is called a Negative Impedance Circuit. It is possible to get a negative resistance with the following circuit. In the problem, assume both BJTs are in the active region. $($BJT has $r_0=)$

$\%$ A positive resistance consumes power, but a negative resistance generate power!!

$$

$(20$ pts$)($a$)$ Draw an AC equivalent circuit using current controlled current T$-$model of BJT$.$ When drawing an $AC$ equivalent circuit, IGNORE bias resistances $R_3,R_4,R_3$;$R_4$ :

$(20$ pts$)($b$)$ From $($a$),$ find