The gain of an amplifier can be nonlinear if the feedback resistors themselves are nonlinear. By shunting feedback resistors with resistor-diode networks, the effective feedback resistance decreases as the input signal increases. If this network is placed across $$R_i$$, then an increasing gain function will be created. If the network is placed across $$R_f$$, then a decreasing gain function will be created. By combining several resistor-diode sections, complex transfer curves can be created.