Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
  • H04N25/50—Control of the SSIS exposure
  • H04N25/57—Control of the dynamic range
  • H04N25/571—Control of the dynamic range involving a non-linear response
  • H04N25/575—Control of the dynamic range involving a non-linear response with a response composed of multiple slopes
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
  • H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
  • H04N25/67—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response
  • H04N25/671—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response for non-uniformity detection or correction
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
  • H04N25/70—SSIS architectures; Circuits associated therewith
  • H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
  • H04N25/77—Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
  • H04N25/70—SSIS architectures; Circuits associated therewith
  • H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
  • H04N25/77—Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
  • H04N25/772—Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components comprising A/D, V/T, V/F, I/T or I/F converters
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
  • H04N25/70—SSIS architectures; Circuits associated therewith
  • H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
  • H04N25/78—Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters

Definitions

• the invention relates generally to the field of image sensors, and more particularly, to such CMOS image sensors in which the image signal is converted into a digital signal immediately after output from the pixel array.
• CMOS image sensors all have the same or substantially the same structures. They typically include the photosensitive devices, like a photodiode or photogate, in the pixel array to convert the optical signal to charge; a floating diffusion capacitor for converting the charge to a voltage; and a pixel amplifier buffering the floating diffusion capacitance from the large output bus capacitance and sending the electrical signal out of the pixel array.
• the pixel output signals are stored by a sample/hold circuit array followed by an analog signal processing chain and an analog-to-digital converter.
• the invention resides in an image sensor comprising (a) a photosensitive region that accumulates charge corresponding to received incident light; (b) a transfer gate for transferring charge from the photosensitive region; (c) a voltage supply having a ramped voltage over time; (d) a floating diffusion for receiving the charge from the photosensitive region and converting the charge to a voltage; (e) an amplifier for receiving and amplifying a signal from the floating diffusion; (f) a comparator for comparing a voltage from the amplifier to a reference voltage; and (g) a counter for counting clock cycles between initiation of the increasing voltage until a signal is received from the comparator indicating charge transfer from the photosensitive region to the floating diffusion.
• the present invention has the advantage of high-speed processing, lower power dissipation and low noise. It further eliminates the effects of non- linearity and threshold variations in the pixel amplifier.
• FIG. 1 is a block diagram of the image sensor of the present invention
• Fig. 2 is a schematic diagram of Fig. 1;
• Fig. 3 is a timing diagram for Fig 2;
• Fig.4a illustrates the image sensor of the present invention in schematic form;
• Fig. 4b illustrates a cross section of the present invention
• Fig. 4c illustrates a well potential diagram for Fig. 4b for clearly illustrating the concept of the present invention.
• Fig. 5 is a digital camera of the present invention for illustrating a typical commercial embodiment for the image sensor of the present invention.
• a image sensor 10 of the present invention having a plurality of pixels 20 and a plurality of sample and hold circuits 30 for receiving and storing the signals from the plurality of pixels 20 in a predetermined manner.
• a plurality of comparators 40 are respectively connected to the output of each sample and hold circuit 30, and a plurality of counters 50 are respectively connected to the plurality of comparators 40.
• Fig. 2 illustrates only one pixel and its associated circuitry of the present invention for illustrating a representative pixel of the plurality of pixels of the present invention for clarity of understanding. It is understood that the present invention includes a plurality of such pixels; for example, the pixel array 20 as shown in Fig. 1. Referring to Fig. 2, the pixel 20 is composed of a photosensitive region or photodiode 60 that accumulates charge in response to incident light.
• a transfer gate 70 receives a ramped voltage over time (preferably an increasing voltage over time) from a voltage supply 95 which causes transfer of charge from the photodiode 60 to a charge-to-voltage conversion region or floating diffusion 80, which converts charge to a voltage signal.
• the increasing voltage is supplied by a voltage supply 95 which is preferably on-chip but outside the pixel array 20.
• the voltage supply 95 may optionally be located off-chip in an alternative embodiment.
• a reset transistor 90 sets a reference voltage for both the floating diffusion 80 and the sample and hold circuit 30, which (in the case of the sample and hold circuit 30) will be subsequently used by the comparator 40, as will be described in detail hereinbelow.
• An amplifier or amplifier transistor 100 receives and amplifies the signal from the floating diffusion 80.
• a row select transistor 110 selects the particular row of pixels for output to the sample and hold circuit 30.
• Fig. 3 includes the preferred timing for Fig. 2 and includes common timing signal acronyms for the timing signal to be applied to a component referred to in Fig. 2 - RS, TG, RG and SHR.
• an image is captured by the plurality of photodiodes 60 during integration, and after integration, a row of pixels in the pixel array is selected for readout by applying a "high" to the gate of row select transistor 110.
• a pulse voltage is then applied to the gate of the reset transistor 90 to clear charge from the floating diffusion (FD) capacitor 80 and to then reset the floating diffusion 80 to the reference voltage.
• the voltage at FD 80 is amplified by the amplifier 100 and sent out to the column bus.
• clock SHR goes from “low” to “high” to close switch S2 and open switch Sl .
• the reference voltage is sampled onto the capacitor (Csh) 120.
• the SHR clock also resets the counter 50.
• a ramped or an increasing voltage over time is applied onto the transfer gate 70 to create a potential underneath the transfer gate 70 for transferring the signal from the photodiode 60 to the floating diffusion 80.
• SHR changes from high to low, switch Sl closes and S2 opens which puts the comparator 40 in the comparing state, and the counter 50 starts counting clock cycles until the comparator 40 signals the counter 50 to terminate counting.
• the comparator 50 compares the pixel output voltage to the sampled reset voltage in each column.
• a digital calibration function is included in the A/D conversion operation by sampling incident light in darkness which is stored in memory (on or off-chip). This calibration signal will be subtracted from the digital signal representing the captured image. The pixel noise and pixel amplifier offset are removed or greatly reduced.
• the image sensor of the present invention detects the electrical charge potential of the photodiode, or in other words, it detects the depth of the unfilled potential well of the photodiode.
• the voltage applied on the gate of the transfer gate 70 controls , the potential underneath the gate and creates a conductive channel when the voltage is higher the threshold voltage of the transfer gate 70.
• the potential well 121 of the photodiode 60 and the floating diffusion area 80 are connected by this created channel of the transfer gate 70.
• the electrical potential underneath the gate is lowered.
• the potential underneath the transfer gate 70 is equal to the electrical potential of the well 121 of the photodiode 60, charge accumulated in the photodiode 60 starts to move from photodiode 60 to the diffusion area 80 through the transfer gate 70.
• the move of charge from photodiode 60 to the floating diffusion 80 will generate a voltage signal at the floating diffusion area 80 which is then sent to the input of the pixel amplifier 100.
• the circuit in the column sample-and-hold array 30 compares the voltage signal at the pixel amplifier output 115 to a previously generated reference voltage when the transfer gate voltage is applied.
• the move of the electrons from photodiode 60 to the floating diffusion 80 will trigger the comparator 40 in the sample-and-hold circuit 30 to change its output state.
• This change of comparator 40 output state stops the counter 50 and a digital code is generated at the counter 50 output.
• This digital code or the digital signal represents the image signal created by the pixel .
• FIG. 5 there is shown a digital camera 125 in which the image sensor 10 of the present invention is disposed for illustrating a preferred commercial embodiment of the present invention.

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Physics & Mathematics (AREA)
• Nonlinear Science (AREA)
• Transforming Light Signals Into Electric Signals (AREA)
• Solid State Image Pick-Up Elements (AREA)

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• 2006
  • 2006-02-15 US US11/354,444 patent/US7652706B2/en active Active
• 2007
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  • 2007-02-07 CN CN200780005721XA patent/CN101385329B/zh active Active
  • 2007-02-07 JP JP2008555278A patent/JP4916517B2/ja active Active
  • 2007-02-07 WO PCT/US2007/003332 patent/WO2007097918A1/en not_active Ceased
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