Suppression of row-wise noise in CMOS image sensors
View Patent ↗Embodiments of circuits and methods for suppressing row-wise noise in the analog domain in an image sensing device. In one embodiment, a pixel sampling circuit includes a readout circuit that is connected to a plurality of pixels to receive analog signals from the pixels. The pixel sampling circuit also includes a noise correction circuit that provides a reference signal to remove at least a portion of the noise in the analog signals received from the pixels before the analog signals are converted into digital signals.
1. A pixel sampling circuit, comprising:
a readout circuit coupled to a plurality of pixels arranged in rows to receive analog pixel signals from each row of pixels of the plurality of pixels; and
a noise correction circuit coupled to the readout circuit operable to sense noise, the noise correction circuit comprising:
a plurality of dark reference pixels arranged in rows, each dark reference pixel of a row of dark reference pixels of the plurality of dark reference pixels being coupled to a respective pixel of a row of pixels of the plurality of pixels, wherein each dark reference pixel is operative to provide at least one reference signal that corresponds to the noise sensed for each respective pixel of the row of pixels to remove at least a portion of a noise component of the pixel signals received from the row of pixels while the pixel signals are analog signals; and
a reference unit comprising a separate dark reference pixel, a transistor, and a capacitor, the separate dark reference pixel not being coupled to the plurality of pixels, and wherein a signal of the separate dark reference pixel is sampled on the capacitor to provide a separate reference signal that is operable to reset an output line of the readout circuit.
2. The pixel sampling circuit of claim 1 wherein the noise correction circuit is operable to generate a plurality of reference signals responsive to noise sensed by the noise correction circuit, each of the plurality of reference signals provided to the readout circuit for a respective pixel of the plurality of pixels.
3. A pixel sampling circuit, comprising:
a readout circuit having a plurality of sampling units arranged in rows, each sampling unit coupled to a respective pixel of a row of pixels to receive analog pixel signals from the respective pixel;
at least one reference unit coupled to the readout circuit, the at least one reference unit operable to sense noise and comprising a row of dark reference pixels, each dark reference pixel of the row of dark reference pixels being coupled to a respective pixel of the row of pixels, wherein each dark reference pixel is operative to provide a reference signal that corresponds to the sensed noise for each respective pixel of the row of pixels to cancel at least a portion of a noise component of the pixel signals received from the row of pixels while the pixel signals are analog signals; and
a separate reference unit coupled to the readout circuit, the separate reference unit comprising a separate dark reference pixel, a transistor, and a capacitor, the separate dark reference pixel not being coupled to the row of pixels, and wherein a signal of the separate dark reference pixel is sampled on the capacitor to provide a separate reference signal that is operable to reset an output line of the readout circuit.
4. The pixel sampling circuit of claim 3 wherein the at least one reference unit comprises a plurality of reference units each of which is coupled to and provides a respective reference signal to and drives a respective sampling unit of the plurality of sampling units.
5. An image sensing circuit, comprising:
an array of light-sensing pixels arranged in rows, each of the light-sensing pixels operable to provide a first signal and a second signal;
a pixel sampling circuit coupled to the array and operable to receive the first and second signals from the array of light-sensing pixels and operable to output corresponding noise-suppressed first and second signals, the pixel sampling circuit comprising:
a plurality of sampling units arranged in rows, each sampling unit of each row of sampling units coupled to a respective light-sensing pixel of a respective row of the array of light-sensing pixels and operable to receive the respective first and second signals from the respective pixel;
a plurality of reference units coupled to the plurality of sampling units, the plurality of reference units operable to sense noise and comprising an array of dark reference pixels arranged in rows, each dark reference pixel of each row of the array of dark reference pixels being coupled to a respective light-sensing pixel of a respective row of the array of light-sensing pixels, wherein each dark reference pixel is operative to provide a reference signal corresponding to the sensed noise to the plurality of sampling units to cancel at least a portion of a noise component of the received first and second signals while the first and second signals are analog signals; and
a separate reference unit comprising a separate dark reference pixel, a transistor, and a capacitor, the separate dark reference pixel not being coupled to the array of light-sensing pixels, and wherein a signal of the separate dark reference pixel is sampled on the capacitor to provide a reference voltage that is operable to reset an output line;
an amplifier circuit coupled to receive the noise-suppressed first and second signals from the pixel sampling circuit, the amplifier circuit operable to generate a plurality of final output signals each of which for a respective light-sensing pixel of the array of light-sensing pixels by amplifying the difference of the respective noise-suppressed first signal and the respective noise-suppressed second signal of each respective light-sensing pixel; and
an analog-to-digital converter coupled to receive the plurality of final output signals from the amplifier circuit and operable to convert each of the plurality of final output signals into a respective digital image signal.
6. The image sensing circuit of claim 5 wherein at least one of each of the plurality of reference units is coupled to a respective sampling unit to provide a respective reference signal to the respective sampling unit.
7. A computer system, comprising:
a data input device;
a data output device;
a data storage device;
a computing circuitry coupled to the data input device, the data output device, and the data storage device, the computing circuitry operable to process data to and from the data input device, the data output device, and the data storage device; and
an image sensing device coupled to the computing circuitry and operable to provide image data representing an image sensed by the image sensing device, the image sensing device comprising:
a plurality of light-sensing pixels arranged in rows and operable to produce pixel signals;
a readout circuit comprising a plurality of readout units each of which is coupled to a respective light-sensing pixel of the plurality of light-sensing pixels to receive the pixel signals from the respective light-sensing pixel;
a plurality of reference units coupled to the readout circuit, the plurality of reference units operable to sense noise and comprising a plurality of dark reference pixels arranged in rows, each dark reference pixel of each row of the plurality of dark reference pixels being coupled to a respective light-sensing pixel of a respective row of the plurality of light-sensing pixels, wherein each dark reference pixel is operative to provide to the readout circuit a respective reference signal that corresponds to noise sensed for each respective light-sensing pixel to remove at least a portion of a noise component of the pixel signals while the pixel signals are analog signals; and
a separate reference unit coupled to the readout circuit, the separate reference unit comprising a separate dark reference pixel, a transistor, and a capacitor, the separate dark reference pixel not being coupled to the plurality of light-sensing pixels, wherein a signal of the separate dark reference pixel is sampled on the capacitor to provide a reference voltage that is operable to reset an output line of the readout circuit.
8. The computer system of claim 7 wherein at least one of each of the plurality of reference units being coupled to a respective readout unit is operable to provide the respective reference signal to the respective readout unit.
9. A consumer device, comprising:
a processor operable to process data, addresses, and commands;
a display device coupled to the processor; and
an input device coupled to the processor, the input device comprising an image sensing device that is operable to provide image data representing image sensed by the image sensing device, the image sensing device comprising:
a plurality of light-sensing pixels arranged in rows and operable to produce pixel signals;
a readout circuit comprising a plurality of readout units each of which is coupled to a respective light-sensing pixel of the plurality of light-sensing pixels to receive the pixel signals from the respective light-sensing pixel;
a plurality of reference units coupled to the readout circuit, the plurality of reference units operable to sense noise and comprising a plurality of dark reference pixels arranged in rows, each dark reference pixel of a row of dark reference pixels of the plurality of dark reference pixels being coupled to a respective light-sensing pixel of a row of light-sensing pixels of the plurality of light-sensing pixels, wherein each dark reference pixel is operative to provide to the readout circuit a respective reference signal that corresponds to noise sensed to remove at least a portion of a noise component of the pixel signals while the pixel signals are analog signals; and
a separate reference unit coupled to the readout circuit, the separate reference unit comprising a separate dark reference pixel, a transistor, and a capacitor, the separate dark reference pixel not being coupled to the plurality of light-sensing pixels, wherein a signal of the separate dark reference pixel is sampled on the capacitor to provide a reference voltage that is operable to reset an output line of the readout circuit.
10. The consumer device of claim 9 wherein at least one of each of the plurality of reference units being coupled to a respective readout unit is operable to provide the respective reference signal to the respective readout unit.
11. The consumer device of claim 9 , further comprising a data storage device for storing data from the processor and the input device.
12. The consumer device of claim 9 , further comprising a peripheral device interface for coupling external devices to the processor.
13. A method for sampling pixel signals, comprising:
receiving pixel signals from at least one pixel of a row of pixels;
providing at least one reference signal that corresponds to at least a portion of noise to which each pixel of the row of pixels are susceptible using a row of dark reference pixels, wherein each dark reference pixel of the row of dark reference pixels is coupled to a respective pixel of the row of pixels;
sampling a signal of a separate dark reference pixel on a capacitor in order to provide a reference voltage that is operable to reset an output line of a readout circuit, wherein the separate dark reference pixel and the capacitor are coupled to a transistor to form a reference unit, the separate dark reference pixel not being coupled to the row of pixels; and
compensating for noise in the received pixel signals with the at least one reference signal before the pixel signals are converted into digital signals.
14. The method of claim 13 wherein providing at least one reference signal that corresponds to at least a portion of noise to which each pixel of the row of pixels are susceptible comprises:
sensing the noise with a plurality of noise-sensing units, wherein each noise-sensing unit of the plurality of noise-sensing units comprises a respective dark reference pixel of the row of dark reference pixels; and
generating a plurality of noise reference signals each of which is generated by one of the plurality of noise-sensing units.
15. The method of claim 14 wherein compensating for noise in the received pixel signals with the at least one reference signal comprises subtracting a noise reference signal generated by a noise-sensing unit of the plurality of noise-sensing units from the pixel signals received from a respective pixel of the row of pixels to which the noise-sensing unit is coupled.
16. The pixel sampling circuit of claim 1 wherein the signal is an output voltage level of the separate dark reference pixel.
17. The pixel sampling circuit of claim 3 wherein the signal is an output voltage level of the separate dark reference pixel.
18. The image sensing circuit of claim 5 wherein the signal is an output voltage level of the separate dark reference pixel.
19. The computer system of claim 7 wherein the signal is an output voltage level of the separate dark reference pixel.
20. The consumer device of claim 9 wherein the signal is an output voltage level of the separate dark reference pixel.
21. The method of claim 13 wherein sampling the signal of the separate dark reference pixel further comprises sampling an output voltage level of the separate dark reference pixel on the capacitor.