An amplifier includes a first capacitor connected between an input node and a floating node, a second capacitor connected between the floating node and an output node, an amplifying element connected between a power supply voltage and the output node and operating in response to a voltage level of the floating node, a current bias source connected between the output node and a ground voltage, a first reset switch connected between the floating node and an intermediate node and operating in response to a reset bias, a second reset switch connected between the intermediate node and the output node and operating in response to the reset bias, and a reset bias generator circuit that outputs the reset bias in response to a reset signal. The reset bias is one of a reset voltage of the intermediate node, the power supply voltage, and the ground voltage.