Image sensing device and method for operating the same
An image sensing device includes a pixel array including a unit pixel suitable to transfer and store charges in response to a transfer signal and read out a pixel signal corresponding to the stored charges in response to a selection signal provided to the unit pixel; a signal converter suitable for comparing the pixel signal with a ramp signal based on a switch signal to generate a distance information signal; and a signal controller suitable for generating the switch signal for initializing the signal converter in a temporal section where the pixel signal is read out.
1. An image sensing device, comprising:
a pixel array including a unit pixel suitable to transfer and store charges in response to a transfer signal and read out at least one pixel signal corresponding to the stored charges in response to a selection signal provided to the unit pixel;
a signal converter suitable for comparing the pixel signal with a ramp signal in response to a switch signal to generate a distance information signal, wherein the ramp signal has a voltage level which rises at a predetermined slope between a low voltage level and a high voltage level; and
a signal controller suitable for generating control signals for controlling the pixel array and the signal converter,
wherein the signal controller comprises
a ramp signal generator suitable for generating the ramp signal and transferring the ramp signal to the signal converter, and
a control signal generator suitable for generating a plurality of row signals for controlling the pixel array on a row basis and generating the switch signal for initializing the signal converter in a temporal read-out section where the pixel signal is read out,
wherein the distance information signal is generated by comparing the voltage level of the rising ramp signal with respective voltages of first and second pixel signals,
wherein the signal converter generates the distance information signal corresponding to a difference between voltage changes of the first and second pixel signals that are reset to respective initial values, in response to the ramp signal.
2. The image sensing device of claim 1 , wherein the signal controller is suitable to generate the selection signal that is activated in the temporal read-out section, and
when the selection signal is activated, the signal controller is suitable to transition the switch signal from a first logic level and to a second logic level.
3. The image sensing device of claim 2 , wherein the signal converter includes:
a first input circuit suitable for receiving the pixel signal to generate an input signal;
a second input circuit suitable for receiving the ramp signal to generate a reference signal;
a comparator suitable for comparing the input signal with the reference signal to output a comparison signal;
a switching circuit suitable for selectively coupling an input node and an output node of the comparator in response to the switch signal; and
a counter suitable for counting a clock signal in response to the comparison signal.
4. The image sensing device of claim 2 , wherein the signal controller is suitable to generate the transfer signal, and wherein the transfer signal is activated when the switch signal transitions, and
the unit pixel is suitable to reset the pixel signal in response to the activated transfer signal.
5. The image sensing device of claim 4 , wherein the unit pixel includes:
a charge storage circuit suitable for storing the charges;
a reset circuit suitable for resetting the charge storage circuit in response to a reset signal;
a transfer circuit suitable for transferring the charges to the charge storage circuit in response to the transfer signal; and
a selection circuit suitable for generating the pixel signal corresponding to the charges stored in the charge storage circuit in response to the selection signal.
6. The image sensing device of claim 5 , wherein the signal controller is suitable to generate the reset signal, and wherein the reset signal is activated simultaneously with the selection signal in the temporal read-out section.
7. The image sensing device of claim 6 , wherein in response to the activated reset signal and the activated transfer signal, respectively,
the reset circuit and the transfer circuit are suitable to initialize the charge storage circuit.
8. The image sensing device of claim 4 , wherein the ramp signal gradually rises from a low voltage level to a high voltage level when the transfer signal is activated.
9. The image sensing device of claim 1 , wherein the unit pixel includes:
a first pixel suitable for generating first charges in response to an optical signal and a first phase signal and generating a first pixel signal corresponding to the first charges in response to the selection signal; and
a second pixel suitable for generating second charges in response to the optical signal and a second phase signal and generating a second pixel signal corresponding to the second charges in response to the selection signal.
10. The image sensing device of claim 9 , wherein the signal converter includes:
a first signal converter suitable for generating a first count signal corresponding to a first voltage level difference between the first pixel signal and the ramp signal;
a second comparator suitable for generating a second count signal corresponding to a second voltage level difference between the second pixel signal and the ramp signal; and
a logic circuit suitable for processing the first count signal and the second count signal to produce count values and to output a difference between the count values as the distance information signal.
11. The image sensing device of claim 9 , wherein the first and second phase signals have a phase difference of 180 degrees.
12. A method for operating an image sensing device, comprising:
reading out, in response to a selection signal, a first pixel signal and a second pixel signal respectively corresponding to a first charges and a second charges that are stored in a unit pixel;
setting an offset voltage between the read-out first and second pixel signals and generating a ramp signal in response to a switch signal, wherein the ramp signal has a voltage level which rises at a predetermined slope between a low voltage level and a high voltage level;
resetting the first and second pixel signals in response to a transfer signal; and
comparing the voltage level of the rising ramp signal with respective voltages of the reset first and second pixel signals and thereby generating a distance information signal corresponding to a voltage change difference between the reset first pixel signal and the reset second pixel signal that are reset to respective initial values, in response to the ramp signal.
13. The method of claim 12 , wherein the selection signal is suitable to be activated in a temporal read-out section where the first and second pixel signals are read out, and
when the selection signal is activated, the switch signal suitable to transition from a first logic level to a second logic level.
14. The method of claim 13 , wherein when the switch signal transitions, the transfer signal is suitable to be activated.
15. The method of claim 14 , wherein when the transfer signal is activated, the ramp signal is suitable to gradually rise from a low voltage to a high voltage.
16. The method of claim 12 , wherein when the generating of the distance information signal includes:
comparing the ramp signal with the reset first pixel signal to generate a first count signal corresponding to a first voltage change of the reset first pixel signal;
comparing the ramp signal with the reset second pixel signal to generate a second count signal corresponding to a second voltage change of the reset second pixel signal; and
processing the first count signal and the second count signal to generate the distance information signal.