Ramp signal generation device and CMOS image sensor including the same

1. A ramp signal generation device, comprising:

a sampling circuit configured to sample a ramp current of the ramp signal generation device and store a voltage corresponding to the sampled ramp current;

a current maintaining circuit configured to maintain the ramp current;

a current transferring circuit configured to transfer a current corresponding to the voltage stored on the sampling circuit;

a current-to-voltage converter configured to convert and generate a ramp voltage corresponding to the current transferred from the current transferring circuit; and

an output circuit configured to stabilize and output the ramp voltage;

wherein the output circuit includes:

a switch coupled between the current-to-voltage converter and an output node; and

a capacitor coupled between the output node and a ground voltage terminal.

2. The ramp signal generation device of claim 1 , wherein the sampling circuit includes:

a capacitor having a first terminal coupled to a power supply voltage terminal, and configured to sample the ramp current and store the voltage corresponding to the sampled ramp current; and

a switching circuit coupled between a second terminal of the capacitor and the current maintaining circuit, and configured to switch the ramp current on or off.

3. The ramp signal generation device of claim 2 , wherein the switching circuit includes:

a first switch having a first terminal coupled to the second terminal of the capacitor, and configured to switch on or off the ramp current; and

a second switch coupled between a second terminal of the first switch and the current maintaining circuit, and configured to switch on or off the ramp current.

4. The ramp signal generation device of claim 1 , wherein the current transferring circuit includes a transistor having a source terminal coupled to a power supply voltage terminal, a gate terminal coupled to the sampling circuit, and a drain terminal coupled to an output node.

5. The ramp signal generation device of claim 1 , wherein the current-to-voltage converter includes:

a third switch having a first terminal coupled to an output node, and configured to switch on or off the current transferred from the current transferring circuit; and

a ramp resistor coupled between a second terminal of the third switch and a ground voltage terminal, and configured to generate the ramp voltage corresponding to the current transferred through the third switch.

6. A complementary metal-oxide-semiconductor (CMOS) image sensor, comprising:

a pixel array including pixels, configured to generate a pixel signal corresponding to incident light received at each pixel;

a row decoder coupled to the pixel array and configured to select and control the pixels of the pixel array row by row;

a ramp signal generation device configured to sample a ramp current, store a voltage corresponding to the sampled ramp current, transfer a current corresponding to the stored voltage to a ramp resistor, and generate a ramp voltage corresponding to the transferred current;

a comparison circuit configured to compare the ramp voltage applied from the ramp signal generation device with the pixel signal received from the pixel array;

a counter configured to perform a counting operation based on the comparison signal;

a memory configured to store information outputted from the counter;

a column read-out circuit configured to output the information stored in the memory; and

a controller configured to control the row decoder, the ramp signal generation device, the comparison circuit, the counter, the memory and the column read-out circuit,

wherein the ramp signal generation device includes:

a sampling circuit configured to sample the ramp current and store the voltage corresponding to the sampled ramp current;

a current maintaining circuit configured to maintain the ramp current;

a current transferring circuit configured to transfer a current corresponding to the voltage;

a current-to-voltage converter configured to convert and generate the ramp voltage corresponding to a current transferred from the current transferring circuit; and

an output circuit configured to stabilize and output the ramp voltage, which is converted by the current-voltage converter,

wherein the output circuit includes:

a switch coupled between the current-to-voltage converter and an output node; and

a capacitor coupled between the output node and a ground voltage terminal.

7. The CMOS image sensor of claim 6 , wherein the sampling circuit includes:

a capacitor having a first terminal coupled to a power supply voltage terminal and configured to sample the ramp current and storing the voltage corresponding to a sampled ramp current; and

a switching circuit coupled between a second terminal of the capacitor and the current maintaining circuit, and configured to switch the ramp current on or off.

8. The CMOS image sensor of claim 6 , wherein the switching circuit includes:

a first switch having a first terminal coupled to the second terminal of the capacitor, and configured to switch on or off the ramp current; and

a second switch coupled between a second terminal of the first switch and the current maintaining circuit, and configured to switch on or off the ramp current.

9. The CMOS image sensor of claim 6 , wherein the current transferring circuit includes a transistor having a source terminal coupled to a power supply voltage terminal, a gate terminal coupled to the sampling circuit, and a drain terminal coupled to an output node.

10. The CMOS image sensor of claim 6 , wherein the current-to-voltage converter includes:

a third switch having a first terminal coupled to an output node, and configured to switch on or off the current transferred from the current transferring circuit; and

a ramp resistor coupled between a second terminal of the third switch and a ground voltage terminal, and configured to generate the ramp voltage corresponding to the current transferred through the third switch.