Ramp voltage generator and image sensor
A ramp voltage generator includes: a ramping cell array including a plurality of ramping current cells; a calibration cell array including a plurality of calibration current cells; and a current-voltage converter suitable for converting a current supplied from activated ramping current cells among the ramping current cells and activated calibration current cells among the calibration current cells into a voltage to generate a ramp voltage.
1. A ramp voltage generator, comprising:
a ramping cell array including a plurality of ramping current cells;
a calibration cell array including a plurality of calibration current cells; and
a current-voltage converter suitable for converting a current supplied from activated ramping current cells among the ramping current cells and activated calibration current cells among the calibration current cells into a voltage to generate a ramp voltage,
wherein each of the ramping current cells is suitable for supplying a unit current of the same amount when activated, and
wherein at least one among the calibration current cells is suitable for supplying a current whose amount is less than the unit current when activated.
2. The ramp voltage generator of claim 1 ,
wherein the calibration current cells include:
current cells each suitable for supplying a current of (the unit current/8) when activated;
current cells each suitable for supplying a current of (the unit current/4) when activated;
current cells each suitable for supplying a current of (the unit current/2) when activated; and
current cells each suitable for supplying the unit current when activated.
3. The ramp voltage generator of claim 1 , wherein the ramping cell array further includes:
a row circuit suitable for controlling activation of the ramping current cells, which are arranged in a plurality of rows and a plurality of columns, in a row direction;
a column circuit suitable for controlling activation of the ramping current cells in a column direction; and
a timing generator suitable for controlling the row circuit and the column circuit.
4. The ramp voltage generator of claim 1 , wherein the calibration cell array further includes a calibration current control circuit suitable for selecting the calibration current cells that are activated in the calibration cell array in response to correction information.
5. The ramp voltage generator of claim 4 , wherein the correction information includes information on a gain of a device including the ramp voltage generator.
6. The ramp voltage generator of claim 4 , wherein the correction information includes information on a level of the power source voltage supplied to the ramp voltage generator.
7. The ramp voltage generator of claim 4 , wherein the current control circuit includes:
a calibration row circuit suitable for controlling activation of the calibration current cells, which are arranged in a plurality of rows and a plurality of columns, in a row direction;
a calibration column circuit suitable for controlling activation of the ramping current cells in a column direction; and
a calibration timing generator suitable for controlling the calibration row circuit and the calibration column circuit.
8. A ramp voltage generator, comprising:
a ramping cell array including a plurality of ramping current cells;
a calibration cell array including a plurality of calibration current cells; and
a current-voltage converter suitable for converting a current supplied from activated ramping current cells among the ramping current cells and activated calibration current cells among the calibration current cells into a voltage to generate a ramp voltage,
wherein the calibration cell array is suitable for supplying a preset current to the current-voltage converter before a ramping operation in which the ramp voltage starts to fall, and suitable for supplying a current of [the preset current-a correction current] to the current-voltage converter after the ramping operation starts.
9. The ramp voltage generator of claim 8 , wherein the calibration cell array is further suitable for increasing an amount of the correction current as an absolute value of a slope of the ramp voltage increases during the ramping operation.
10. The ramp voltage generator of claim 8 , wherein the calibration cell array is further suitable for increasing an amount of the correction current as a gain of a device including the ramp voltage generator decreases.
11. The ramp voltage generator of claim 8 , wherein when fluctuation of a power source voltage supplied to the ramp voltage generator is detected during the ramping operation, the calibration cell array is further suitable for adjusting an amount of current supplied to the current-voltage converter.
12. The ramp voltage generator of claim 11 , wherein when a decrease of the power source voltage is detected during the ramping operation, the calibration cell array increases the amount of current supplied to the current-voltage converter.
13. The ramp voltage generator of claim 11 , wherein when an increase of the power source voltage is detected during the ramping operation, the calibration cell array decreases the amount of current supplied to the current-voltage converter.
14. The ramp voltage generator of claim 8 , wherein the ramping cell array is suitable for supplying a maximum current to the current-voltage converter before the ramping operation, and suitable for decreasing an amount of current supplied to the current-voltage converter after the ramping operation starts.
15. An image sensor, comprising:
a pixel array suitable for outputting a pixel signal corresponding to incident light;
a row decoder suitable for selecting and controlling pixels in the pixel array for each row;
a ramp voltage generator suitable for generating a ramp voltage; and
an analog-to-digital conversion circuit suitable for analog-to-digital conversion of the pixel signal based on the ramp voltage,
wherein the ramp voltage generator includes:
a ramping cell array including a plurality of ramping current cells;
a calibration cell array including a plurality of calibration current cells; and
a current-voltage converter suitable for generating the ramp voltage by converting a current supplied from activated ramping current cells among the ramping current cells and activated calibration current cells among the calibration current cells into a voltage,
wherein each of the ramping current cells is suitable for supplying a unit current of the same amount when activated, and
wherein at least one among the calibration current cells is suitable for supplying a current whose amount is less than the unit current when activated.
16. An image sensor, comprising:
a pixel array suitable for outputting a pixel signal corresponding to incident light;
a row decoder suitable for selecting and controlling pixels in the pixel array for each row;
a ramp voltage generator suitable for generating a ramp voltage; and
an analog-to-digital conversion circuit suitable for analog-to-digital conversion of the pixel signal based on the ramp voltage,
wherein the ramp voltage generator includes:
a ramping cell array including a plurality of ramping current cells;
a calibration cell array including a plurality of calibration current cells; and
a current-voltage converter suitable for generating the ramp voltage by converting a current supplied from activated ramping current cells among the ramping current cells and activated calibration current cells among the calibration current cells into a voltage,
wherein the calibration cell array is suitable for supplying a preset current to the current-voltage converter before a ramping operation in which the ramp voltage starts to fall, and suitable for supplying a current of [the preset current-a correction current] to the current-voltage converter after the ramping operation starts.
17. The image sensor of claim 16 , wherein the calibration cell array is further suitable for increasing an amount of the correction current as a gain of the analog-to-digital conversion circuit decreases.
18. The image sensor of claim 16 , wherein when fluctuation of a power source voltage supplied to the ramp voltage generator is detected during the ramping operation, the calibration cell array is further suitable for adjusting an amount of current supplied to the current-voltage converter.
19. A ramp voltage generator comprising:
a converter suitable for generating a ramp voltage from a ramp current and a calibration current during a ramp operation;
a ramping circuit suitable for providing the converter with the ramp current according to gain information, the ramp current linearly decreasing from its maximum during the ramp operation; and
a calibration circuit suitable for:
providing the converter with the calibration current having a preset level at start of the ramp operation,
decreasing the calibration current by a predetermined amount according to the gain information during the ramp operation, and
adjusting the amount according to power information indicating fluctuation of a power voltage supplied to the generator.