Image sensing device for generating HDR image and imaging device including the same
An image sensing device includes: a pixel configured to output a reference signal corresponding to a sensing node that is reset and an image signal corresponding to the sensing node in which photocharges are accumulated, in each of a high conversion gain (HCG) mode and a low conversion gain (LCG) mode; an analog-to-digital converter (ADC) configured to sequentially perform analog-to-digital conversion of the reference signal of the HCG mode, the image signal of the HCG mode, the image signal of the LCG mode, and the reference signal of the LCG mode; and a ramp generator configured to generate a first ramp signal that is used for analog-to-digital conversion in the HCG mode, and to generate a second ramp signal that is used for analog-to-digital conversion in the LCG mode while having a waveform different from that of the first ramp signal.
1 . An image sensing device comprising:
a pixel configured to output a reference signal corresponding to a sensing node that is reset and an image signal corresponding to the sensing node in which photocharges are accumulated, in each of a high conversion gain (HCG) mode in which the sensing node has a first capacitance and a low conversion gain (LCG) mode in which the sensing node has a second capacitance greater than the first capacitance;
an analog-to-digital converter (ADC) configured to sequentially perform analog-to-digital conversion of the reference signal of the HCG mode, the image signal of the HCG mode, the image signal of the LCG mode, and the reference signal of the LCG mode; and
a ramp generator configured to generate a first ramp signal having a negative slope, the first ramp signal being used for analog-to-digital conversion in the HCG mode, and to generate a second ramp signal having a positive slope, the second ramp signal being used for analog-to-digital conversion in the LCG mode while having a waveform different from that of the first ramp signal,
wherein the analog-to-digital converter (ADC) comprises:
a comparator configured to generate comparison data indicating a result of comparison between a pixel signal having both the reference signal and the image signal and a ramp signal having both the first ramp signal and the second ramp signal; and
a counter configured to generate ADC data indicating a result of counting in a period in which the comparison data is at a logic high level, and
wherein the comparator comprises:
a non-inverting terminal configured to receive the first ramp signal in the HCG mode and receive the pixel signal in the LCG mode; and
an inverting terminal configured to receive the pixel signal in the HCG mode and receive the second ramp signal in the LCG mode.
2 . The image sensing device according to claim 1 , wherein:
the ramp generator is configured to perform an auto-zeroing operation for adjusting a pixel signal having both the reference signal and the image signal and a ramp signal having both the first ramp signal and the second ramp signal, at each of a time point at which the HCG mode is started and a time point at which the LCG mode is started.
3 . The image sensing device according to claim 1 , wherein:
the slope of the first ramp signal and the slope of the second ramp signal have the same absolute value.
4 . The image sensing device according to claim 1 , wherein the ramp generator comprises:
a bidirectional ramp generator configured to generate the first ramp signal or the second ramp signal in response to a dual conversion gain (DCG) control signal for selecting the HCG mode or the LCG mode.
5 . The image sensing device according to claim 1 , wherein the ramp generator comprises:
a negative ramp generator configured to generate the first ramp signal; and
a positive ramp generator configured to generate the second ramp signal.
6 . The image sensing device according to claim 1 , wherein the pixel further includes:
a dual conversion gain (DCG) transistor connected between the sensing node and a dual conversion gain (DCG) capacitor, wherein the DCG transistor is turned off in the HCG mode and is turned on in the LCG mode.
7 . An imaging device comprising:
an image sensing device configured to generate image data based on each of a reference signal corresponding to a sensing node that is reset and an image signal corresponding to the sensing node in which photocharges are accumulated, in each of a high conversion gain (HCG) mode in which the sensing node has a first capacitance and a low conversion gain (LCG) mode in which the sensing node has a second capacitance greater than the first capacitance; and
an image signal processor configured to generate a high dynamic range (HDR) image using image data generated in the HCG mode and image data generated in the LCG mode,
wherein the image sensing device comprises:
an analog-to-digital converter (ADC) configured to sequentially perform analog-to-digital conversion of the reference signal of the HCG mode, the image signal of the HCG mode, the image signal of the LCG mode, and the reference signal of the LCG mode; and
a ramp generator configured to generate a first ramp signal having a negative slope, the first ramp signal being used for analog-to-digital conversion in the HCG mode and to generate a second ramp signal having a positive slope, the second ramp signal being used for analog-to-digital conversion in the LCG mode while having a waveform different from that of the first ramp signal,
wherein the ADC comprises a comparator that has a non-inverting terminal for receiving the first ramp signal and the second ramp signal in each of the HCG mode and the LCG mode and an inverting terminal for receiving the pixel signal in each of the HCG mode and the LCG mode; and
wherein the image signal processor subtracts a reference value obtained by conversion of the reference signal of the LCG mode from a sum of a signal value obtained by conversion of the image signal of the LCG mode and a margin value, and acquires image data corresponding to a voltage difference between the image signal and the reference signal in the LCG mode.
8 . An image sensing device comprising:
a pixel configured to output a reference signal corresponding to a sensing node that is reset and an image signal corresponding to the sensing node in which photocharges are accumulated, in each of a high conversion gain (HCG) mode in which the sensing node has a first capacitance and a low conversion gain (LCG) mode in which the sensing node has a second capacitance greater than the first capacitance;
an analog-to-digital converter (ADC) configured to sequentially perform analog-to-digital conversion of the reference signal of the HCG mode, the image signal of the HCG mode, the image signal of the LCG mode, and the reference signal of the LCG mode; and
a ramp generator configured to generate a first ramp signal that is used for analog-to-digital conversion in the HCG mode, and to generate a second ramp signal that is used for analog-to-digital conversion in the LCG mode,
wherein each of the first ramp signal and the second ramp signal has a negative slope; and
wherein a voltage level at which the second ramp signal starts to fall for readout of the image signal of the LCG mode is lower by a signal offset than a voltage level at which the second ramp signal starts to fall for readout of the reference signal of the LCG mode.