Image sensor ADC and CDS per column

• US 7,518,646 B2
• Filed: 09/20/2005
• Issued: 04/14/2009
• Est. Priority Date: 03/26/2001
• Status: Expired due to Fees

• Current Assignee: Dynamax Imaging, LLC
• Original Assignee: Panavision Imaging LLC
• Inventors: Zarnowski, Jeffrey J., Poonnen, Thomas, Karia, Ketan V.
• Primary Examiner(s): Tran; Sinh N
• Assistant Examiner(s): Lam; Hung H
• Application Number:
  US11/230,385
• Publication Number:
  US 20060012696A1
• Time in Patent Office: 1,302 Days
• Field of Search: 348/302, 348/298
• US Class Current: 348/302
• CPC Class Codes: H03M 1/1019 by storing a corrected or correction value in a digital look-up table
• CPC Class Codes: H03M 1/123 Simultaneous, i.e. using one converter per channel but with common control or reference circuits for multiple converters
• CPC Class Codes: H03M 1/1235 Non-linear conversion not otherwise provided for in subgroups of H03M1/12
• CPC Class Codes: H03M 1/56 Input signal compared with linear ramp
• CPC Class Codes: H04N 25/00 Circuitry of solid-state image sensors [SSIS]; Control thereof
• CPC Class Codes: H04N 25/745 Circuitry for generating timing or clock signals
• CPC Class Codes: H04N 25/75 Circuitry for providing, modifying or processing image signals from the pixel array
• CPC Class Codes: H04N 25/767 Horizontal readout lines, multiplexers or registers
• CPC Class Codes: H04N 25/772 comprising A/D, V/T, V/F, I/T or I/F converters

Abstract

A solid state imager converts analog pixel values to digital form on an arrayed per-column basis. An N-bit counter supplies an N-bit DAC to produce an analog ramp output with a level that varies corresponding to the contents of the counter. A ripple counter or equivalent is associated with each respective column. A clock supplies clock signals to the counter elements. A comparator in each column gates the counter element when the analog ramp equals the pixel value for that column. The contents of the counters are transferred sequentially to a video output bus to produce the digital video signal. Additional black-level readout counter elements can create and store a digital value that corresponds to a dark or black video level. A subtraction element subtracts the black level value from the pixel value to reduce fixed pattern noise. An additional array of buffer counter/latches can be employed. The ripple counters can be configured as counters to capture the digital video level, and then as shift registers to clock out the video levels to an output bus. The clock pulses for the DAC counter and for the ripple counters can be at the same or different rates.

Claims

1. Arrangement for converting analog pixel values from an array of pixels to a digital video signal, said array comprising a plurality of columns and at least one row, each column having at one pixel therein, and each column providing a respective pixel value;

the arrangement comprising

a source of clock signals;

an N-bit counter coupled to said source of clock signals;

an N-bit DAC connected to said counter and having a ramp output providing a signal corresponding to a count existing on said counter;

a plurality of digital counter/latch elements each associated with a respective one of said columns and each also coupled to said source of clock signals;

a plurality of comparators each associated with a respective one of said columns, and having one input connected to receive the respective column pixel value, another input connected to the ramp output of said N-bit counter, and a comparator output connected to a gating terminal of the respective digital counter/latch element;

a video readout bus; and

means selectively transferring contents of said digital counter/latch elements to said video output bus to produce said digital video signal.

2. Arrangement of claim 1 wherein each said digital counter/latch element includes a ripple counter.

3. Arrangement of claim 1 further comprising a plurality of black-level readout counter/latch elements, each associated with a respective one of said columns;

each black level readout counter/latch element having an input connected to said source of clock signals and a gating element connected to the respective comparator output;

a black-level readout bus;

means for transferring the contents of the respective black-level counter/latch elements to the black-level readout bus simultaneously with the transfer of the contents of the associated digital counter/latch elements to said video readout bus; and

a subtraction element connected to the video readout bus and the black-level readout bus.

4. Arrangement of claim 1 wherein said digital counter/latch elements each include a first ripple counter member having an input element coupled to said source of clock signals and said comparator, and a buffer latch/counter member having an input connected to an output of the respective first ripple counter member, a gate terminal, and an output connected to the video readout bus;

and means providing a transfer signal to the gate terminals of said buffer counter/latch members.

5. Arrangement of claim 1, wherein said video readout bus comprises a sequence of DQ flip-flops.

6. Arrangement of claim 1, wherein said source of clock signals provides clock signals at different frequencies for the N-bit counter and for the counter/latch elements, respectively.

7. Arrangement for converting analog pixel values from an array of pixels to a digital video signal, said array comprising a plurality of columns and at least one row, each column having at one pixel therein, and each column providing a respective pixel value;

the arrangement comprising an N-bit counter;

an N-bit DAC connected to said counter and having a ramp output providing a signal corresponding to a count existing on said counter;

a plurality of digital latch/counter elements each associated with a respective one of said columns;

a plurality of comparators each associated with a respective one of said columns, said latch/counter elements having an input elements to receive clock pulses and also being coupled to the associated comparator;

wherein each comparator is made up of a differential-input amplifier, each of the amplifiers having a plurality of at least the first input transistor(s), one of the first input transistors located at each of the pixels with in the periphery, and a second input transistor located outside the periphery of the array and coupled to the first input transistors and to an output configuration circuit, and having one input connected to receive the respective column pixel value, another input connected to the ramp output of said N-bit DAC, and a comparator output connected to a gating terminal of the respective digital latch/counter element;

a video readout bus; and

means selectively transferring contents of said digital latch/counter elements to said video output bus to produce said digital video signal.

8. Arrangement of claim 7 wherein each said digital latch/counter element includes a ripple counter.

9. Arrangement of claim 7 further comprising a plurality of black-level readout latch/counter elements, each associated with a respective one of said columns;

each black level readout latch/counter element having a clock input element connected to receive clocking pulses with a gating terminal connected to the respective comparator output;

a black-level readout bus;

means for transferring the contents of the respective black-level latch/counter elements to the black-level readout bus simultaneously with the transfer of the contents of the associated digital latch/counter elements to said video readout bus; and

a subtraction element connected to the video readout bus and the black-level readout bus.

10. Arrangement of claim 7 wherein said digital storage elements each include a first latch/counter member having a clock input, and a buffer latch/counter member, having an input connected to an output of the respective first latch/counter member, a gate terminal, and an output connected to the video readout bus;

and means providing a transfer signal to the gate terminals of said buffer latch/counter members.

11. Arrangement of claim 7, wherein said video readout bus comprises a sequence of DQ flip-flops.

12. Arrangement of claim 7, further comprising clock generator means providing clocking pulses at different respective clock frequencies to said N-bit counter and to said latch counter elements.

13. Arrangement for converting analog pixel values from an array of pixels to a digital video signal, said array comprising a plurality of columns and at least one row, each column having at one pixel therein, and each column providing a respective pixel value;

the arrangement comprising

a source of clock signals;

an N-bit counter coupled to said source of clock signals;

an N-bit DAC connected to said counter and having a ramp output providing a signal corresponding to a count existing on said counter;

a plurality of digital counter/latch elements each associated with a respective one of said columns and each also coupled to said source of clock signals;

a plurality of comparators each associated with a respective one of said columns, and having one input connected to receive the respective column pixel value, another input connected to the ramp output of said N-bit counter, and a comparator output connected to a gating terminal of the respective digital counter/latch element; and

wherein each said digital counter/latch element is formed of a plurality of flip-flops including control inputs to receive a LATCH signal and a READ OUT signal, respectively, such that when said LATCH signal is applied the digital counter/latch elements count said clock signals to store a value corresponding to the respective pixel value, and when said READ OUT signal is applied said digital counter/latch elements are configured as a shift register and serve as means sequentially transferring contents of said digital counter/latch elements to a video output bus to produce said digital video signal.

14. The arrangement of claim 13, wherein said source of clock signals provides said clock signals at different frequencies to said N-bit counter and to said counter/latch elements, respectively.

15. The arrangement of claim 13, wherein said N-bit DAC provides ramps of different slope for different rows of pixels of said array.