Various technologies described herein pertain to controlling floating diffusion gain using a charge pump. Feedback can be utilized to control impedance of a floating diffusion region of a pixel of an image sensor, which further includes a read bus and an amplifier. The pixel includes a capacitor and a floating diffusion region, which has an intrinsic floating diffusion capacitance. The capacitor includes a first terminal and a second terminal, where the first terminal is coupled to the floating diffusion region. The amplifier includes an input terminal and an output terminal. The input terminal of the amplifier is coupled to the read bus and the output terminal of the amplifier is coupled to the second terminal of the capacitor. Gain of the amplifier is adjustable to control an equivalent capacitance of the floating diffusion region. Alteration of the equivalent capacitance can modify conversion gain and dynamic range of the pixel.