A ramp signal generator is provided. The ramp signal generator includes a bias generation circuit, a transferring switch, a sampling capacitor, a current cell circuit, a current to voltage converter and a tuning circuit. The bias generation circuit generates a bias voltage. The transferring switch transfers the bias voltage to a sampling node in response to a first switching control signal. The sampling capacitor samples the bias voltage. The current cell circuit provides a first output node with a first ramping current in response to a sampled bias voltage and switching code pairs. The current to voltage converter includes a first load resistor to convert the first ramping current to a first ramp signal. The tuning circuit includes a capacitor that couples the sampled bias voltage to the first ramp signal, and adjusts a degree of nonlinearity of the first ramp signal in response to a tuning signal.