A ramp signal generator is provided, and includes a sampling capacitor, a current cell circuit, a current to voltage converter, and a tuning circuit. The sampling capacitor is connected between a power supply voltage and a sampling node. The current cell circuit provides a first output node with a first ramping current during a ramping period, in response to a sampled bias voltage of the sampling node and switching code pairs. The current to voltage converter includes a first load resistor connected between the first output node and a ground voltage, and converts the first ramping current to a first ramp signal. The tuning circuit is connected between the first output node and the sampling node, and includes a capacitor to couple the sampling node and the first output node. The tuning circuit adjusts a degree of nonlinearity of the first ramp signal in response to a tuning signal.
