Ramp signal generator for calibrating ramp linearity, operating method thereof, and image sensor device including the same

An image sensor device comprising:

• a pixel array configured to output pixel signals corresponding to an image;
• a ramp signal generator configured to output a ramp signal;
• an analog-to-digital converter configured to receive the pixel signals from the pixel array and to receive the ramp signal from the ramp signal generator;
• and
• a sensor controller configured to control the ramp signal generator, and to generate a plurality of first sub-ramp control signals and a plurality of second sub-ramp control signals,
• wherein the ramp signal generator comprises:
• a first unit current source comprising a plurality of first sub-unit current sources, and configured to output a first unit current during a first time period;
• and
• a second unit current source comprising a plurality of second sub-unit current sources, and configured to output a second unit current during a second time period,
• wherein the plurality of first sub-unit current sources are configured to operate according to the plurality of first sub-ramp control signals, respectively,
• wherein the plurality of second sub-unit current sources are configured to operate according to the plurality of second sub-ramp control signals, respectively, and
• wherein n first sub-ramp control signals among the plurality of first sub-ramp control signals are activated, and m sub-ramp control signals among the plurality of second sub-ramp control signals are activated, n and m being different natural numbers.

A ramp signal generator comprising:

• a first unit current source configured to output a first unit current during a first time period;
• and
• a second unit current source configured to output a second unit current during a second time period,
• wherein the ramp signal generator is configured to generate a ramp signal having a voltage level that changes from a first value to a second value,
• wherein a magnitude of the first unit current and a magnitude of the second unit current are different from each other,
• wherein the magnitude of the first unit current is identical to a magnitude of a unit current for generating a target ramp signal during the first time period,
• wherein the magnitude of the second unit current is identical to the magnitude of the unit current for generating the target ramp signal during the second time period, and
• wherein the target ramp signal has a voltage level that changes linearly from the first value to the second value.