Image sensor with processor controlled integration time
Claim Score by NHIP
Abstract
An image sensor that has one or more pixels within a pixel array. The pixels are arranged within a plurality of rows within the array. Each row of the pixel array can be selected by a row decoder in response to an edge of a control signal. The control signal may be one of a plurality of signals generated by a processor coupled to the image sensor. The processor can control the exposure time of the pixels by varying the control signals. The control signals may also have an embedded narrow pulse that is used to determine the location of a "window" in the pixel array.

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20 claims: 3 independent, 17 dependent
- 1An image sensor that is connected to a processor which generates a plurality of control signals, the control signals including a first edge separated from a second edge by a control interval, comprising:a pixel array that contains a plurality of rows of pixels;and, a selection circuit that selects a row of said pixel array to generate and retrieve pixel data from said pixel array by resetting and reading said selected row of said pixel array, a time interval between the resetting and reading of said selected row being proportional to the control interval between the first and second edges.
- 10An image sensor that is connected to a processor which generates a plurality of control signals including a first pulse that has a first width and a second pulse that has a different second width, comprising:a pixel array that contains a plurality of rows of pixels;and, a selection circuit that selects a group of rows of said pixel array, the group being a function of a location of the second pulse relative to the first pulse.
- 19Broadest claimClaim Score 83, broad(NHIP)An image sensor, comprising:a pixel array that contains a plurality of rows of pixels;an address decoder coupled to a row of said pixel array;a multiplexor coupled to said address decoder;a first address generator coupled to said multiplexor;and, a second address generator coupled to said multiplexor.
Independent claims3
82 paragraphs in 5 sections, as filed
REFERENCE TO CROSS RELATED APPLICATION
P-0001[0001] This application claims priority under 35 U.S.C §119(e) to provisional application No. 60/372,902 filed on Apr. 16, 2002.
BACKGROUND OF THE INVENTION
P-0002[0002] 1. Field of the Invention
P-0003[0003] The subject matter disclosed generally relates to the field of semiconductor image sensors.
P-0004[0004] 2. Background Information
P-0005[0005] Photographic equipment such as digital cameras and digital camcorders contain electronic image sensors that capture light for processing into a still or video image, respectively. There are two primary types of electronic image sensors, charge coupled devices (CCDs) and complimentary metal oxide semiconductor (CMOS) sensors. CCD image sensors have relatively high signal to noise ratios (SNR) that provide quality images. Additionally, CCDs can be fabricated to have pixel arrays that are relatively small while conforming with most camera and video resolution requirements. A pixel is the smallest discrete element of an image. For these reasons, CCDs are used in most commercially available cameras and camcorders.
P-0006[0006] CMOS sensors are faster and consume less power than CCD devices. Additionally, CMOS fabrication processes are used to make many types of integrated circuits. Consequently, there is a greater abundance of manufacturing capacity for CMOS sensors than CCD sensors.
P-0007[0007] To date there has not been developed a CMOS sensor that has the same SNR and pixel pitch requirements as commercially available CCD sensors. Pixel pitch is the space between the centers of adjacent pixels. It would be desirable to provide a CMOS sensor that has relatively high SNR while providing a commercially acceptable pixel pitch.
P-0008[0008] The image sensor is typically connected to an external processor and external memory. The external memory stores data from the image sensor. The processor processes the stored data. The data includes one or more images generated by exposing the pixels for a predetermined time interval. The exposure time of the pixels is typically controlled by an internal clock(s) of the image sensor.
P-0009[0009] The exposure time of a picture frame is established by a word written into an exposure time register. Changing the exposure time requires writing new data into the register and then reading the data. In video and fast successive still photo shots this technique may create confusion regarding the exposure time of incoming pixel data, thereby creating instability in the system. It would be desirable to provide processor control of the exposure time of the pixels that improves stability and does not require an undesirable number of pins and signals.
P-0010[0010] Camera or camcorder products typically have an auto-focus function. To increase the speed of an auto-focus cycle the camera may be designed to process only a “window” of the pixel array. The auto-focus routine may require the window to move around the pixel array of the image sensor. It would be desirable to provide processor control of the window data in a manner that minimizes the pin count and number of signals required for the image sensor.
BRIEF SUMMARY OF THE INVENTION
P-0011[0011] An image sensor coupled to a process that generates a plurality of control signals. The image sensor includes a pixel array that is arranged into a number of rows. The sensor may also contain a logic circuit that selects a row of the pixel array to generate and retrieve pixel data in response to a first edge and a second edge of the control signals. A time interval between a resetting and a reading of the selected row is proportional to an interval between the first and second edges of the control signals.
BRIEF DESCRIPTION OF THE DRAWINGS
P-0012[0012] FIGS. <b>1</b> is a schematic of an embodiment of an image sensor;
P-0013[0013]FIG. 2 is a schematic of an embodiment of a pixel of the image sensor;
P-0014[0014]FIG. 3 is a schematic of an embodiment of a light reader circuit of the image sensor;
P-0015[0015]FIG. 4 is a flowchart for a first mode of operation of the image sensor;
P-0016[0016]FIG. 5 is a timing diagram for the first mode of operation of the image sensor;
P-0017[0017]FIG. 6 is a diagram showing the levels of a signal across a photodiode of a pixel;
P-0018[0018]FIG. 7 is a schematic for a logic circuit for generating the timing diagrams of FIG. 5;
P-0019[0019]FIG. 8 is a schematic of a logic circuit for generating a RST signal for a row of pixels;
P-0020[0020]FIG. 9 is a timing diagram for the logic circuit shown in FIG. 8;
P-0021[0021]FIG. 10 is a flowchart showing a second mode of operation of the image sensor;
P-0022[0022]FIG. 11 is a timing diagram for the second mode of operation of the image sensor;
P-0023[0023]FIG. 12 is a schematic of an embodiment of a row decoder of the image sensor;
P-0024[0024]FIG. 13 is a timing diagram for the row decoder shown in FIG. 12;
P-0025[0025]FIG. 14 is a timing diagram showing the transfer of pixel data when the image sensor is in a low noise mode;
P-0026[0026]FIG. 15 is a timing diagram showing the transfer of pixel data when the image sensor is in an extended dynamic range mode;
P-0027[0027]FIG. 16 is an illustration of a window of the pixel array;
P-0028[0028]FIG. 17 is timing diagram showing an embedded narrow pulse used to determine a start location of the window.
DETAILED DESCRIPTION
P-0029[0029] Disclosed is an image sensor that has one or more pixels within a pixel array. The pixels are arranged within a plurality of rows within the array. Each row of the pixel array can be selected by a row decoder in response to an edge of a control signal. The control signal may be one of a plurality of signals generated by a processor coupled to the image sensor. The processor can control the exposure time of the pixels by varying the control signals. The control signals may also have an embedded narrow pulse that is used to determine the location of a “window” in the pixel array.
P-0030[0030] The pixel may be a three transistor structure that minimizes the pixel pitch of the image sensor. The entire image sensor is preferably constructed with CMOS fabrication processes and circuits. The CMOS image sensor has the characteristics of being high speed, low power consumption, small pixel pitch and a high SNR.
P-0031[0031] Referring to the drawings more particularly by reference numbers, FIG. 1 shows an image sensor <b>10</b>. The image sensor <b>10</b> includes a pixel array <b>12</b> that contains a plurality of individual photodetecting pixels <b>14</b>. The pixels <b>14</b> are arranged in a two-dimensional array of rows and columns.
P-0032[0032] The pixel array <b>12</b> is coupled to a light reader circuit <b>16</b> by a bus <b>18</b> and to a row decoder <b>20</b> by control lines <b>22</b>. The row decoder <b>20</b> can select an individual row of the pixel array <b>12</b>. The light reader <b>16</b> can then read specific-discrete columns within the selected row. Together, the row decoder <b>20</b> and light reader <b>16</b> allow for the reading of an individual pixel <b>14</b> in the array <b>12</b>.
P-0033[0033] The light reader <b>16</b> may be coupled to an analog to digital converter <b>24</b> (ADC) by output line(s) <b>26</b>. The ADC <b>24</b> generates a digital bit string that corresponds to the amplitude of the signal provided by the light reader <b>16</b> and the selected pixels <b>14</b>.
P-0034[0034] The ADC <b>24</b> may be coupled to line buffers <b>28</b> by data lines <b>30</b>. The line buffers <b>28</b> may include separate pairs of buffers for first image data and second image data. The line buffers <b>28</b> are coupled to a data interface <b>32</b> that transfers data to a processor <b>34</b> over bus <b>36</b>. The processor <b>34</b> may be coupled to memory <b>38</b> by bus <b>40</b>. Although the memory <b>38</b> is shown coupled to the processor <b>34</b>, it is to be understood that the system may have other configurations. For example, the processor <b>34</b> and memory <b>38</b> may be coupled to the interface <b>32</b> by separate busses.
P-0035[0035] The data interface <b>32</b> may be connected to a control line INTG <b>42</b> which provides a control signal from the processor <b>34</b>. The control signal may contain a series of pulses that control the transfer of data to the processor <b>34</b>. The pixel data may be transferred to the processor <b>34</b> in an interleaving manner. For example, the buffers <b>28</b> may store pixel data of a first image and a second image. The data interface <b>32</b> may interleave the data by sending a first line of the first image and then a first line of the second image and so forth and so on.
P-0036[0036] The image sensor <b>10</b> may have registers <b>44</b> that store mode and gain values. The values can be provided to the data interface <b>32</b>, buffers <b>28</b>, light reader <b>16</b> and row decoder <b>20</b> over lines <b>46</b>, <b>48</b>, <b>50</b> and <b>52</b>, respectively. The values can be loaded into the registers <b>44</b> through lines <b>54</b>, <b>56</b> and <b>58</b>. The image sensor <b>10</b> may also have clock circuits <b>60</b> that provide CLK timing signals over line <b>62</b>.
P-0037[0037] The light reader circuit <b>16</b> may be coupled to a column decoder <b>64</b> by control lines <b>66</b>. The decoder <b>64</b> selects a column within the pixel array <b>12</b> to generate and retrieve pixel data from the pixels <b>14</b>. The decoder <b>64</b> is coupled to a counter <b>68</b> by a bus <b>70</b>. The counter <b>68</b> provides a count value that causes the decoder <b>64</b> to switch the selection of a column in the pixel array <b>12</b>. Counter <b>68</b> is also connected to an input line HD <b>72</b> and an output line HDF <b>74</b>.
P-0038[0038] The row decoder <b>20</b> may include a plurality of row drivers <b>76</b> that are coupled to the pixel array <b>12</b>. The row drivers <b>76</b> may be coupled to decoders <b>78</b> and counters <b>80</b>. The counters <b>80</b> may be coupled to a counter/latch circuit <b>82</b>.
P-0039[0039] The row decoder <b>20</b> may also include a phase sequence decoder <b>84</b>. The phase sequence decoder <b>84</b> may be coupled to the light reader <b>16</b>, row drivers <b>76</b> and decoders <b>78</b> by control signals <b>86</b>. The row decoder <b>20</b> may further include a wide pulse detector <b>88</b> and a narrow pulse detector <b>90</b>. The wide pulse detector <b>88</b> may be connected to the counters <b>80</b> by LEAD <b>92</b> and LAG <b>94</b> control signals, respectively. The narrow pulse detector <b>90</b> may be connected to the counter/latch <b>82</b> by control signal NP <b>96</b>. The pulse detectors <b>88</b> and <b>90</b> may be connected to the INTG control line <b>42</b> that is coupled to the processor <b>34</b>. The counter/latch <b>82</b>, narrow pulse detector <b>90</b> and phase sequence decoder <b>84</b> may be connected to the mode line <b>52</b> of register <b>44</b>.
P-0040[0040]FIG. 2 shows an embodiment of a cell structure for a pixel <b>14</b> of the pixel array <b>12</b>. The pixel <b>14</b> may contain a photodetector <b>100</b>. By way of example, the photodetector <b>100</b> may be a photodiode. The photodetector <b>100</b> may be connected to a reset transistor <b>112</b>. The photodetector <b>100</b> may also be coupled to a select transistor <b>114</b> through a level shifting transistor <b>116</b>. The transistors <b>112</b>, <b>114</b> and <b>116</b> may be field effect transistors (FETs).
P-0041[0041] The gate of reset transistor <b>112</b> may be connected to a RST line <b>118</b>. The drain node of the transistor <b>112</b> may be connected to IN line <b>120</b>. The gate of select transistor <b>114</b> may be connected to a SEL line <b>122</b>. The source node of transistor <b>114</b> may be connected to an OUT line <b>124</b>. The RST <b>118</b> and SEL lines <b>122</b> may be common for an entire row of pixels in the pixel array <b>12</b>. Likewise, the IN <b>120</b> and OUT <b>124</b> lines may be common for an entire column of pixels in the pixel array <b>12</b>. The RST line <b>118</b> and SEL line <b>122</b> are connected to the row decoder <b>20</b> and are part of the control lines <b>22</b>.
P-0042[0042]FIG. 3 shows an embodiment of a light reader circuit <b>16</b>. The light reader <b>16</b> may include a plurality of double sampling capacitor circuits <b>150</b> each connected to an OUT line <b>124</b> of the pixel array <b>12</b>. Each double sampling circuit <b>150</b> may include a first capacitor <b>152</b> and a second capacitor <b>154</b>. The first capacitor <b>152</b> is coupled to the OUT line <b>124</b> and ground GND<b>1</b><b>156</b> by switches <b>158</b> and <b>160</b>, respectively. The second capacitor <b>154</b> is coupled to the OUT line <b>124</b> and ground GND<b>1</b> by switches <b>162</b> and <b>164</b>, respectively. Switches <b>158</b> and <b>160</b> are controlled by a control line SAM<b>1</b><b>166</b>. Switches <b>162</b> and <b>164</b> are controlled by a control line SAM<b>2</b><b>168</b>. The capacitors <b>152</b> and <b>154</b> can be connected together to perform a voltage subtraction by closing switch <b>170</b>. The switch <b>170</b> is controlled by a control line SUB <b>172</b>.
P-0043[0043] The double sampling circuits <b>150</b> are connected to an operational amplifier <b>180</b> by a plurality of first switches <b>182</b> and a plurality of second switches <b>184</b>. The amplifier <b>180</b> has a negative terminal−coupled to the first capacitors <b>152</b> by the first switches <b>182</b> and a positive terminal+coupled to the second capacitors <b>154</b> by the second switches <b>184</b>. The operational amplifier <b>180</b> has a positive output+connected to an output line OP <b>188</b> and a negative output−connected to an output line OM <b>186</b>. The output lines <b>186</b> and <b>188</b> are connected to the ADC <b>24</b> (see FIG. 1).
P-0044[0044] The operational amplifier <b>180</b> provides an amplified signal that is the difference between the voltage stored in the first capacitor <b>152</b> and the voltage stored in the second capacitor <b>154</b> of a sampling circuit <b>150</b> connected to the amplifier <b>180</b>. The gain of the amplifier <b>180</b> can be varied by adjusting the variable capacitors <b>190</b>. The variable capacitors <b>190</b> may be discharged by closing a pair of switches <b>192</b>. The switches <b>192</b> may be connected to a corresponding control line (not shown). Although a single amplifier is shown and described, it is to be understood that more than one amplifier can be used in the light reader circuit <b>16</b>.
P-0045[0045]FIGS. 4 and 5 show an operation of the image sensor <b>10</b> in a first mode also referred to as a low noise mode. In process block <b>300</b> a reference signal is written into each pixel <b>14</b> of the pixel array and then a first reference output signal is stored in the light reader <b>16</b>. Referring to FIGS. 2 and 5, this can be accomplished by switching the RST <b>118</b> and IN <b>120</b> lines from a low voltage to a high voltage to turn on transistor <b>112</b>. The RST line <b>118</b> is driven high for an entire row. IN line <b>120</b> is driven high for an entire column. In the preferred embodiment, RST line <b>118</b> is first driven high while the IN line <b>120</b> is initially low.
P-0046[0046] The RST line <b>118</b> may be connected to a tri-state buffer (not shown) that is switched to a tri-state when the IN line <b>120</b> is switched to a high state. This allows the gate voltage to float to a value that is higher than the voltage on the IN line <b>120</b>. This causes the transistor <b>112</b> to enter the triode region. In the triode region the voltage across the photodiode <b>100</b> is approximately the same as the voltage on the IN line <b>120</b>. Generating a higher gate voltage allows the photodetector to be reset at a level close to Vdd. CMOS sensors of the prior art reset the photodetector to a level of Vdd-Vgs, where Vgs can be up to 1 V.
P-0047[0047] The SEL line <b>122</b> is also switched to a high voltage level which turns on transistor <b>114</b>. The voltage of the photodiode <b>100</b> is provided to the OUT line <b>124</b> through level shifter transistor <b>116</b> and select transistor <b>114</b>. The SAM<b>1</b> control line <b>166</b> of the light reader <b>16</b> (see FIG. 3) is selected so that the voltage on the OUT line <b>124</b> is stored in the first capacitor <b>152</b>.
P-0048[0048] Referring to FIG. 4, in process block <b>302</b> the pixels of the pixel array are then reset and reset output signals are then stored in the light reader <b>16</b>. Referring to FIGS. 2 and 5 this can be accomplished by driving the RST line <b>118</b> low to turn off the transistor <b>112</b> and reset the pixel <b>14</b>. Turning off the transistor <b>112</b> will create reset noise, charge injection and clock feedthrough voltage that resides across the photodiode <b>100</b>. As shown in FIG. 6 the noise reduces the voltage at the photodetector <b>100</b> when the transistor <b>112</b> is reset.
P-0049[0049] The SAM<b>2</b> line <b>168</b> is driven high, the SEL line <b>122</b> is driven low and then high again, so that a level shifted voltage of the photodiode <b>100</b> is stored as a reset output signal in the second capacitor <b>154</b> of the light reader circuit <b>16</b>. Process blocks <b>300</b> and <b>302</b> are repeated for each pixel <b>14</b> in the array <b>12</b>.
P-0050[0050] Referring to FIG. 4, in process block <b>304</b> the reset output signals are then subtracted from the first reference output signals to create noise output signals that are then converted to digital bit strings by ADC <b>24</b>. The digital output data can be stored within the line buffers <b>28</b> and eventually transferred and stored within the external memory <b>38</b>. The noise signals may be referred to as a first image. Referring to FIG. 3, the subtraction process can be accomplished by closing switches <b>182</b>, <b>184</b> and <b>170</b> of the light reader circuit <b>16</b> (FIG. 3) to subtract the voltage across the second capacitor <b>154</b> from the voltage across the first capacitor <b>152</b>.
P-0051[0051] Referring to FIG. 4, in block <b>306</b> light response output signals are sampled from the pixels <b>14</b> of the pixel array <b>12</b> and stored in the light reader circuit <b>16</b>. The light response output signals correspond to the optical image that is being detected by the image sensor <b>10</b>. Referring to FIGS. 2, 3 and <b>5</b> this can be accomplished by having the IN <b>120</b>, SEL <b>122</b> and SAM<b>2</b> lines <b>168</b> in a high state and RST <b>118</b> in a low state. The second capacitor <b>152</b> of the light reader circuit <b>16</b> stores a level shifted voltage of the photodiode <b>100</b> as the light response output signal.
P-0052[0052] Referring to FIG. 4, in block <b>308</b> a second reference output signal is then generated in the pixels <b>14</b> and stored in the light reader circuit <b>16</b>. Referring to FIGS. 2, 3 and <b>5</b>, this can be accomplished similar to generating and storing the first reference output signal. The RST line <b>118</b> is first driven high and then into a tri-state. The IN line <b>120</b> is then driven high to cause the transistor <b>112</b> to enter the triode region so that the voltage across the photodiode <b>100</b> is the voltage on IN line <b>120</b>. The SEL <b>122</b> and SAM<b>2</b><b>168</b> lines are then driven high to store the second reference output voltage in the first capacitor <b>154</b> of the light reader circuit <b>16</b>. Process blocks <b>306</b> and <b>308</b> are repeated for each pixel <b>14</b> in the array <b>12</b>.
P-0053[0053] Referring to FIG. 4, in block <b>310</b> the light response output signal is subtracted from the second reference output signal to create a normalized light response output signal. The normalized light response output signal is converted into a digital bit string to create normalized light output data that is transferred to the processor <b>34</b>. The normalized light response output signals may be referred to as a second image. Referring to FIGS. 2, 3 and <b>5</b> the subtraction process can be accomplished by closing switches <b>170</b>, <b>182</b> and <b>184</b> of the light reader <b>16</b> to subtract the voltage across the first capacitor <b>152</b> from the voltage across the second capacitor <b>154</b>. The difference is then amplified by amplifier <b>180</b> and converted into a digital bit string by ADC <b>24</b> as light response data.
P-0054[0054] Referring to FIG. 4, in block <b>312</b> the noise data is retrieved from memory <b>38</b>. In block <b>314</b> the noise data, first image, is combined (subtracted) with the normalized light output data, second image, by the processor <b>34</b>. The noise data corresponds to the first image and the normalized light output data corresponds to the second image. The second reference output signal is the same or approximately the same as the first reference output signal such that the present technique subtracts the noise data, due to reset noise, charge injection and clock feedthrough, from the normalized light response signal. This improves the signal to noise ratio of the final image data.
P-0055[0055] The process described is performed in a sequence across the various rows of the pixels in the pixel array <b>12</b>. As shown in FIG. 5, the n-th row in the pixel array may be generating noise signals while the n-<b>1</b>-th row generates normalized light response signals, where <b>1</b> is the exposure duration in multiples of a line period.
P-0056[0056] The various control signals RST, SEL, IN, SAM<b>1</b>, SAM<b>2</b> and SUB can be generated in the circuit generally referred to as the phase sequence decoder <b>84</b>. FIG. 7 shows an embodiment of logic to generate the IN, SEL, SAM<b>1</b>, SAM<b>2</b> and RST signals in accordance with the timing diagram of FIG. 5. The logic may include a plurality of comparators <b>350</b> with one input connected to a counter <b>68</b> and another input connected to hardwired signals that contain a lower count value and an upper count value. The counter <b>68</b> sequentially generates a count. The comparators <b>350</b> compare the present count with the lower and upper count values. If the present count is between the lower and upper count values the comparators <b>350</b> output a logical 1.
P-0057[0057] The comparators <b>350</b> are connected to plurality of AND gates <b>356</b> and OR gates <b>358</b>. The OR gates <b>358</b> are connected to latches <b>360</b>. The latches <b>360</b> provide the corresponding IN, SEL, SAM<b>1</b>, SAM<b>2</b> and RST signals. The AND gates <b>356</b> are also connected to a mode line <b>364</b>. To operate in accordance with the timing diagram shown in FIG. 5, the mode line <b>364</b> is set at a logic 1.
P-0058[0058] The latches <b>360</b> switch between a logic 0and a logic 1 in accordance with the logic established by the AND gates <b>356</b>, OR gates <b>358</b>, comparators <b>350</b> and the present count of the counter <b>352</b>. For example, the hardwired signals for the comparator coupled to the IN latch may contain a count values of <b>6</b> and a count value of <b>24</b>. If the count from the counter is greater or equal to 6 but less than 24 the comparator <b>350</b> will provide a logic 1 that will cause the IN latch <b>360</b> to output a logic 1. The lower and upper count values establish the sequence and duration of the pulses shown in FIG. 5. The mode line <b>364</b> can be switched to a logic 0 which causes the image sensor to function in a second mode.
P-0059[0059] The sensor <b>10</b> may have a plurality of reset RST(n) drivers <b>370</b>, each driver <b>370</b> being connected to a row of pixels. FIGS. 8 and 9 show an exemplary driver circuit <b>370</b> and the operation of the circuit <b>370</b>. Each driver <b>370</b> may have a pair of NOR gates <b>372</b> that are connected to the RST and SAM<b>1</b> latches shown in FIG. 7. The NOR gates control the state of a tri-state buffer <b>374</b>. The tri-state buffer <b>374</b> is connected to the reset transistors in a row of pixels. The input of the tri-state buffer is connected to an AND gate <b>376</b> that is connected to the RST latch and a row enable ROWEN(n) line.
P-0060[0060]FIGS. 10 and 11 show operation of the image sensor in a second mode also referred to as an extended dynamic range mode. In this mode the image provides a sufficient amount of optical energy so that the SNR is adequate even without the noise cancellation technique described in FIGS. <b>4</b> and <b>5</b>. Although it is to be understood that the noise cancellation technique shown in FIGS. 4 and 5 can be utilized while the image sensor <b>10</b> is in the extended dynamic range mode. The extended dynamic mode has both a short exposure period and a long exposure period. Referring to FIG. 10, in block <b>400</b> each pixel <b>14</b> is reset to start a short exposure period. The mode of the image sensor can be set by the processor <b>34</b> through register <b>44</b> to determine whether the sensor should be in the low noise mode, or the extended dynamic range mode.
P-0061[0061] In block <b>402</b> a short exposure output signal is generated in the selected pixel and stored in the second capacitor <b>154</b> of the light reader circuit <b>16</b>.
P-0062[0062] In block <b>404</b> the selected pixel is then reset. The level shifted reset voltage of the photodiode <b>100</b> is stored in the first capacitor <b>152</b> of the light reader circuit <b>16</b> as a reset output signal. The short exposure output signal is subtracted from the reset output signal in the light reader circuit <b>16</b>. The difference between the short exposure signal and the reset signal is converted into a binary bit string by ADC <b>24</b> and stored into the external memory <b>38</b>. The short exposure data corresponds to the first image pixel data. Then each pixel is again reset to start a long exposure period.
P-0063[0063] In block <b>406</b> the light reader circuit <b>16</b> stores a long exposure output signal from the pixel in the second capacitor <b>154</b>. In block <b>408</b> the pixel is reset and the light reader circuit <b>16</b> stores the reset output signal in the first capacitor <b>152</b>. The long exposure output signal is subtracted from the reset output signal, amplified and converted into a binary bit string by ADC <b>24</b> as long exposure data.
P-0064[0064] Referring to FIG. 10, in block <b>410</b> the short exposure data is retrieved from memory <b>38</b>. In block <b>412</b> the short exposure data is combined with the long exposure data by the processor <b>34</b>. The data may be combined in a number of different manners. The external processor <b>34</b> may first analyze the image with the long exposure data. The photodiodes may be saturated if the image is too bright. This would normally result in a “washed out” image. The processor <b>34</b> can process the long exposure data to determine whether the image is washed out, if so, the processor <b>34</b> can then use the short exposure image data. The processor <b>34</b> can also use both the long and short exposure data to compensate for saturated portions of the detected image.
P-0065[0065] By way of example, the image may be initially set to all zeros. The processor <b>34</b> then analyzes the long exposure data. If the long exposure data does not exceed a threshold then N least significant bits (LSB) of the image is replaced with all N bits of the long exposure data. If the long exposure data does exceed the threshold then N most significant bits (MSB) of the image are replaced by all N bits of the short exposure data. The image data is N+M bits per pixel. This technique increases the dynamic range by M bits, where M is the exponential in an exposure duration ratio of long and short exposures that is defined by the equation l=2<sup>M</sup>. The replaced image may undergo a logarithmic mapping to a final picture of N bits in accordance with the mapping equation Y=2<sup>N </sup>log<sub>2 </sub>(X)/(N+M).
P-0066[0066]FIG. 11 shows the timing of data generation and retrieval for the long and short exposure data. The reading of output signals from the pixel array <b>12</b> overlap with the retrieval of signals from memory <b>38</b>. FIG. 11 shows timing of data generation and retrieval wherein a n-th row of pixels starts a short exposure, the (n-k)-th row ends the short exposure period and starts the long exposure period, and the (n-k-<b>1</b>)-th row of pixels ends the long exposure period. Where k is the short exposure duration in multiples of the line period, and <b>1</b> is the long exposure duration in multiples of the line period.
P-0067[0067] The processor <b>34</b> begins to retrieve short exposure data for the pixels in row (n-k) at the same time as the (n-k-<b>1</b>)-th row in the pixel array is completing the long exposure period. At the beginning of a line period, the light reader circuit <b>16</b> retrieves the short exposure output signals from the (n-k)-th row of the pixel array <b>12</b> as shown by the enablement of signals SAM<b>1</b>, SAM<b>2</b>, SEL(n-k) and RST(n-k). The light reader circuit <b>16</b> then retrieves the long exposure data of the (n-k-<b>1</b>)-th row.
P-0068[0068] The dual modes of the image sensor <b>10</b> can compensate for varying brightness in the image. When the image brightness is low the output signals from the pixels are relatively low. This would normally reduce the SNR of the resultant data provided by the sensor, assuming the average noise is relatively constant. The noise compensation scheme shown in FIGS. 4 and 5 improve the SNR of the output data so that the image sensor provides a quality picture even when the subject image is relatively dark. Conversely, when the subject image is too bright the extended dynamic range mode depicted in FIGS. 10 and 11 compensates for such brightness to provide a quality picture. Although a process having a short exposure followed by a long exposure is shown and described, it is to be understood that the short exposure may follow the long exposure.
P-0069[0069]FIG. 12 shows an embodiment of a row driver <b>76</b> and adecoder <b>78</b> of the row decoder <b>20</b>. The decoder <b>20</b> may contain an address decoder <b>500</b> and a latch <b>502</b>. The input of the latch <b>502</b> is connected to input lines CLR <b>504</b>, D<b>0</b>, D<b>1</b><b>506</b> from the phase decoder circuit <b>84</b> (see FIG. 1) and the output line LE <b>508</b> of the address decoder <b>500</b>. Although a phase decoder circuit <b>84</b> is shown and described, it is to be understood that any state value generator may be utilized. The input of the driver <b>76</b> is connected to output lines Q<b>0</b>, Q<b>1</b><b>510</b> of the latch <b>502</b> and input lines RST <b>512</b> and SEL <b>514</b> from the phase sequence decoder <b>84</b>. The latches <b>502</b> for each row of pixels are all connected to the phase decoder circuit <b>84</b> by the same common control lines <b>504</b> and <b>506</b>. The common control lines <b>504</b> and <b>506</b> minimize the lines, transistors and space required by the row decoder while providing a means for loading the state valves with a time division muliplexing process.
P-0070[0070] The address decoder <b>500</b> is coupled to a multiplexor <b>520</b> by an address bus <b>522</b>. The address decoder <b>500</b> is also connected to control lines PRE# <b>524</b> and EVA# <b>526</b> from the phase sequence decoder <b>84</b>. The multiplexor <b>520</b> may have three input address busses <b>528</b>, <b>530</b> and <b>532</b>. The address busses <b>528</b>, <b>530</b> and <b>532</b> are connected to a first counter <b>534</b>, a second counter <b>536</b> and a third counter <b>538</b>, respectively. Although counters <b>534</b>, <b>536</b> and <b>538</b> are shown and described, it is to be understood that any address generator may be implemented.
P-0071[0071] The output of the multiplexor <b>520</b> is switched between the busses <b>528</b>, <b>530</b> and <b>532</b> by a control line PA <b>540</b> from the phase sequence decoder <b>84</b>. There is a corresponding address decoder <b>500</b> and latch <b>502</b> for each row of the pixel array <b>12</b>. The multiplexor <b>520</b> provides a time division multiplexing means for selecting a row of the pixel array with a reduced number of lines and transistors which minimizes the size of the image sensor.
P-0072[0072]FIGS. 13 and 14 show an operation of the row decoder <b>20</b> and transfer of pixel data. As shown in FIG. 14, the integration time and transfer of data is dependent on the control signal INTG from the processor <b>34</b>. Making the integration time and data transfer dependent on the control signal INTG allows the processor <b>34</b> to control and vary these parameters.
P-0073[0073] The INTG control signal contains a plurality of pulses each with a falling edge and a rising edge. Referring to FIGS. 1, 12, <b>13</b> and <b>14</b>, a falling edge is detected by the wide pulse detector <b>88</b>, which generates an output on the LEAD control line <b>92</b>. The LEAD control signal starts the first counter <b>534</b>. The first counter <b>534</b> outputs an address that is provided to the multiplexor <b>520</b>.
P-0074[0074] The PA control signal switches some of the multiplexors <b>520</b> to provide the address from the first counter <b>534</b> to the corresponding address decoders <b>500</b>. If the address from the first counter <b>534</b> matches a stored address within the address decoder <b>500</b> the decoder <b>500</b> will enable the latch <b>502</b> through line LE <b>508</b>. The latch <b>502</b> loads state values Q<b>0</b> and Q<b>1</b> into the row driver <b>76</b>. The output state values correspond to state values D<b>0</b> and D<b>1</b> that were previously loaded into the latch <b>502</b> from the phase sequence decoder <b>84</b>. When in low noise mode the state values allow for the RST and SEL signals to pass through the driver <b>76</b> to the selected row to generate and retrieve reference and reset signals, the first image.
P-0075[0075] The first counter <b>534</b> continues to output new address values which in turn sequentially select rows of the pixel array <b>12</b> to allow for the generation and retrieval of reference and noise signals for each row. The falling edge of the INTG control signal also enables the transfer of the first image to the processor <b>34</b> from the data interface <b>32</b>. The process continues until all of the first image data is transferred to the processor <b>34</b>, and stored in memory <b>38</b>.
P-0076[0076] A rising edge of a pulse is detected by the wide pulse detector <b>88</b> which generates an output on the LAG control line <b>94</b>. The LAG signal initiates the second counter <b>536</b>. The second counter <b>536</b> provides addresses that are provided to the multiplexors <b>520</b> of each row. The multiplexors <b>520</b> mux the addresses to the decoders <b>500</b>. If the addresses match, the latch <b>502</b> is enabled to load state values into the row drivers <b>76</b>. When in the low noise mode the state values allow for the generation and retrieval of light response and reference signals for the second image. The rising edge also enables the data interface <b>32</b> to transfer the second image data to the processor <b>34</b>. As shown in FIG. 14, the transfer of first and second image data may overlap. The interface <b>32</b> can transfer the overlapping data to the processor <b>34</b> in an interleaving manner.
P-0077[0077]FIG. 15 shows the transfer of data when the image sensor <b>10</b> is in the extended dynamic range mode. In this mode the INTG control signal includes a narrow pulse between wide pulses. Short exposure is initiated by the falling edge of a wide pulse. The narrow pulse is detected by the narrow pulse detector <b>90</b> which initiates the third counter <b>538</b>. The third counter <b>538</b> provides addresses which are decoded by matching decoders <b>500</b> to enable corresponding latches <b>502</b>. The enabled latches <b>502</b> load state values into the row drivers <b>76</b> that allow for the generation and retrieval of long exposure and reference signals of the second image. The narrow pulse also enables the data interface <b>32</b> to transfer the short exposure and reference signals of the first image to the processor <b>34</b>.
P-0078[0078] The processor <b>34</b> can change the exposure time by varying the width of the pulses in the control signal. The variation in pulse width is an integer multiple of the line period so that the change in pulse width is in synchronization with the signals generated by the phase sequence decoder <b>82</b>. When in the extended dynamic range mode the exposure time can be varied by changing the location of the narrow pulse.
P-0079[0079] As shown in FIG. 16, the image sensor may generate data within a window <b>550</b> of the pixel array <b>12</b>. The window <b>550</b> is an area typically offset from the first row of the pixel array <b>12</b>. The window information may be provided to the processor <b>34</b> to auto-focus the camera. In auto-focus mode the window offset may vary to capture different parts of the image.
P-0080[0080]FIG. 17 shows an INTG control signal with an in embedded narrow pulse that is used to determine the offset location of the window <b>550</b>. When the register <b>44</b> sets the image sensor in a window mode, the narrow pulse detector <b>90</b> detects the embedded narrow pulse and provides a START control signal to the counter/latch <b>82</b> on the NP control line <b>96</b>. The wide pulse detector <b>88</b> detects the rising edge of the next pulse and provides a STOP control signal to the counter/latch <b>82</b> on the LAG control line <b>94</b>. The counter/latch <b>82</b> uses the START and STOP control signal to determine the offset for the window. An offset value is loaded into the counters <b>534</b>, <b>536</b> and <b>538</b> to provide an initial count value. The processor <b>34</b> can control the window offset by varying the location of the embedded narrow pulse within the control signal.
P-0081[0081] It is the intention of the inventor that only claims which contain the term “means” shall be construed under 35 U.S.C. §112, sixth paragraph.
P-0082[0082] While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.
Contents5
15 sheets
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69 transactions on the USPTO file
Abandoned after 3 non-final rejections, 3 final rejections and 2 RCEs.
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| Mail Final Rejection (PTOL - 326)Final rejectionMCTFR | MCTFR | |
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| Examiner Interview Summary Record (PTOL - 413)EXIN | EXIN | |
| Miscellaneous Incoming LetterLET. | LET. | |
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| Date Forwarded to ExaminerFWDX | FWDX | |
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| Date Forwarded to ExaminerFWDX | FWDX | |
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Numbers
- Application
- 38345003
Titles
- English
- Image sensor with processor controlled integration time
Classification
- CPC, 5
- H04N25/42
- H04N25/443
- H04N25/533
- H04N25/589
- H04N25/616
- IPC, 3
- H04N23 40
- H04N25 00
- H04N25 42
- USPC, 1
- 348308000