\small K_U = \cfrac {s^2} { \cfrac {1} {C_1 \, C_2 \, R_1 \, R_2} + s \left( \cfrac {1} {C_2 \, (R_1 || R_2)} + \cfrac {R_2 + R_0} {C_1 \, R_1 \, R_2} \right) + s^2 \left( 1 + \cfrac {R_0} {R_1 || R_2} \right) }