Ramp voltage generator, image sensing device and operating method of the same

An image sensor, comprising:

• a pixel array comprising plural pixels;
• a driver configured to output a reset signal and a transfer signal to the pixel array;
• a convertor configured to perform a first comparison operation for sensing a noise, outputted from the pixel array based on the reset signal, to perform a second comparison operation for sensing raw data, outputted from the pixel array based on the transfer signal, and to output data which is obtained by removing the noise from the raw data;
• and
• a ramp voltage generator configured to generate a ramp voltage used for the first comparison operation and the second comparison operation and to output the ramp voltage to the convertor;
• and
• a data output circuit configured to collect the data outputted from the convertor and to generate image data,
• wherein the ramp voltage is settled to a target level after being boosted over the target level by a boost current which is supplied until the ramp voltage has a level higher than the target level.

A method for operating an image sensor comprising a ramp voltage generator supplying a ramp voltage to a convertor configured to perform a first comparison operation for sensing a noise transferred from a pixel array and to perform a second comparison operation for sensing raw data transferred from the pixel array, the method comprising:

• generating a bias current in response to a first control signal for generating the ramp voltage;
• generating a boost current in response to a second control signal for generating the ramp voltage;
• and
• generating the ramp voltage based on the bias current and the boost current,
• wherein the boost current is supplied until the ramp voltage has a level higher than a target level, and the ramp voltage is settled to the target level after being boosted over the target level.