Calculate the limit frequency \$fg\$ of the attenuation \$v_u =\frac{ u_a} { u_e}\$ at the current source I (for the value given in example), so that for \$f>> fg\$ exist ideal behavior.
Note: First consider each capacitor individually by setting the impedance 0 and consider which of the resulting frequencies is relevant.
My problem:
I solved first part of example for \$C_2 \mapsto \infty\$, but I am having problem with another part.
\$C_1 \mapsto \infty\$
\$v_u =\frac{ u_a} { u_e}= \frac{r_D || (\frac{1}{i \omega C_2} +R_L)}{r_D || (\frac{1}{i \omega C_2} +R_L) +R} =\frac{r_D(1+iR_L\omega C_2)}{i\omega C_2(r_DR_L+r_DR+RR_L)+r_D+R}=\frac{r_D}{r_D+R}\frac{X}{1+iY}\$
So I dont know how to get the last step, how to write it in that form, because \$ Y=\frac{1}{\omega_g}\$ and after that I can find \$f_g\$ easy.