I would like to find transfer function between input signal \$U_1\$ and output signal \$U_2\$. So, I know how to find the transfer function of each op-amp, for example,
1 transfer function: $$\frac{v_o}{v_i} = -\frac{R_3}{R_1}\frac{1}{1+R_3C_3 s}$$
2 transfer function: $$\frac{v_o}{v_i} = -\frac{1}{C_4 s R_4}$$
3 transfer function: $$\frac{v_o}{v_i} = \frac{R_2}{2R}$$
Is that correct way to find $$G(s)=\frac{U_2}{U_1}$$? How can I do it?
Best Answer
For my opinion, the simplest solution makes use of the classical feedback formula from H. Black:
$$\frac{V_2}{V_1}=\frac{H(s)}{1-LG}$$
with:
Note that \$H(s)\$ is positive and the loop gain \$LG\$ must be negative (three inverting stages in series). The transfer functions of the three blocks are basic (inverting lowpass, inverting integrator, inverting amplifier).