Image sensor device and method

Abstract

The present invention discloses an image sensor device and method. The image sensor device includes a sensor array and a processing circuit. The sensor array includes a plurality of pixel units. The pixel unit includes a photodiode unit and a storage capacitor. When the image sensor device performs an exposure operation, the photodiode unit is illuminated to generate a photodiode current to generate an image of a specific frame. The photodiode current is stored in the storage capacitor. Before the exposure operation of generating the specific frame begins, the processing circuit is used to generate a reference current according to the photodiode current of the photodiode unit of the pixel unit, and then estimate the length of the exposure time segment of the exposure operation for generating the specific frame based on the generated reference current. The image sensor device can operate at a low frame rate to save more power and avoid power consumption, and can be used in different light conditions.

Description

Technical Field

[0001] The present application relates to an image sensing mechanism, and more particularly to an image sensor device and a corresponding method. Background Art

[0002] Generally speaking, conventional image sensor devices are not able to estimate the appropriate exposure time period until many frames have been sensed, which is inefficient. Furthermore, when operating at a low frame rate, conventional image sensor devices may frequently move from one surface position to another surface position corresponding to a different light condition, that is, the light condition may have changed before the number of sensed frames is sufficient to estimate the appropriate exposure time period. Thus, when operating at a low frame rate, conventional image sensor devices often encounter the problem of drastic changes in light conditions. Summary of the invention

[0003] Therefore, one of the objectives of the present invention is to disclose an image sensor device and method to solve the above-mentioned problems.

[0004] According to an embodiment of the present invention, an image sensor device is disclosed, which includes a sensor array and a processing circuit. The sensor array includes a plurality of pixel units, and the pixel unit includes a photodiode unit and a storage capacitor. When the image sensor device performs an exposure operation, the photodiode unit is illuminated to generate a photodiode current to generate an image of a specific frame, and the photodiode current is stored in the storage capacitor. The processing circuit is coupled to the sensor array. Before the exposure operation of generating the specific frame begins, the processing circuit is used to generate a reference current according to the photodiode current of the photodiode unit of the pixel unit, and then estimate the length of the exposure time segment of the exposure operation used to generate the specific frame based on the generated reference current.

[0005] According to an embodiment of the present invention, a method for an image sensor device is disclosed, the method comprising: providing a sensor array, the sensor array comprising pixel units, the pixel units comprising photodiode units and storage capacitors; using the sensor array to generate an image of a specific frame, when the image sensor device performs an exposure operation, the photodiode units are illuminated to generate photodiode currents, and the photodiode currents are stored in the storage capacitors; before the exposure operation for the specific frame begins to be performed, a reference current is generated according to the photodiode currents of the photodiode units of the pixel units; and, based on the generated reference current, the length of an exposure time segment of the exposure operation for the specific frame is estimated.

[0006] The image sensor device and method provided by the present invention can dynamically adjust the length of the exposure time segment according to the ambient light conditions, so that the image sensor device can be used and applied in different light conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a block diagram of an image sensor device according to an embodiment of the present application.

[0008] Figure 2 FIG. 4 is a schematic diagram showing an example of the predicted length of the exposure time segment, the signal waveforms of the reset control signal RST, the voltage Vsh, the control signal EN and the output signal SH_OUT.

[0009] Figure 3 is a schematic diagram of an example of an image sensor device according to another embodiment of the present invention.

[0010] Figure 4 is a block diagram of an image sensor device according to an embodiment of the present invention.

[0011] The reference numerals are described as follows:

[0012] 100, 300, 400 Image sensor device

[0013] 105 Sensor Array

[0014] 106_1~106_N pixel unit

[0015] 110 Processing circuit

[0016] 115 Control Circuit

[0017] 1101 Current Mirror Circuit

[0018] 1102 Comparator DETAILED DESCRIPTION

[0019] The present application aims to provide a technical solution for an image sensor device that can predict or estimate the length of an appropriate exposure time segment of an exposure operation, that is, the exposure opening time of the shutter, and the exposure operation is for one or more specific frames, such as the next one or more frames. The technical solution can be applicable to a global shutter mode and a rolling shutter mode. For example, the sensor can operate at a low frame rate, such as a frame rate below 100 Hz to save more power and avoid power consumption, and it is also possible to know how to adjust the length of the shutter exposure opening time.

[0020] Figure 11 is a block diagram of an image sensor device 100 according to an embodiment of the present application. The image sensor device 100 includes a sensor array 105, a processing circuit 110 and a control circuit 115. The processing circuit 110 is coupled to the sensor array 105, a reference voltage level (e.g., a photodiode supply voltage level VDDPD), a reference voltage level (e.g., a pixel supply voltage level VDDPXL) and a ground level GN. The processing circuit 110 includes a current mirror circuit 1101, a reference capacitor (or also referred to as a sampling / holding capacitor) Csh, a comparator 1102 and four switch units SW1-SW4, the four switch units SW1-SW4 are composed of Figure 1 The current mirror circuit 1101 is formed by two transistor circuits M1 and M2. Each transistor circuit M1 and M2 includes one or more PNP or NPN transistors (but not limited to).

[0021] The sensor array 105 is used to generate one or more images of one or more frames, and includes a plurality of pixel units, such as N pixel units 106_1-106_N, and each pixel unit 106_1-106_N includes a photodiode unit PD and a storage capacitor Cpd. Furthermore, each pixel unit 106_1-106_N includes a reset transistor M3, a source follower transistor M4, a read transfer capacitor C1, and a read transfer transistor M5. When the image sensor device 100 performs an exposure operation, the photodiode unit PD is irradiated by light to generate a photodiode current, which is stored in the storage capacitor Cpd.

[0022] The processing circuit 110 is used to generate a reference current according to one or more photodiode currents of one or more photodiode units PD of one or more pixel units before the exposure operation for a specific frame (the next or following frame) is performed. The processing circuit 110 is then used to predict a length of an appropriate exposure time segment for the exposure operation for the specific frame based on the generated reference current.

[0023] For the circuit structure of each pixel unit 106_1-106_N, the reset transistor M3 has a first terminal, a second terminal and a control terminal, wherein the first terminal is coupled to the photodiode supply voltage level VDDPD, the second terminal is coupled to the photodiode unit PD, and the control terminal is coupled to a reset signal RST and controlled by the reset signal RST. The photodiode unit PD is coupled between the ground level GND and the second terminal of the reset transistor M3. The storage capacitor Cpd is also coupled between the ground level GND and the second terminal of the reset transistor M3.

[0024] During a shutter turn-on period, a photodiode current Iphoton is generated due to the illumination of light, and a voltage Vpd is generated at one end of the storage capacitor Cpd. The source follower transistor M4 has a first end, a second end and a control end, wherein the first end is coupled to a pixel supply voltage level VDDPXL, the second end is coupled to a current source I1, and the control end is coupled to the voltage Vpd, so that the source follower transistor M4 can transmit the voltage Vpd to the second end. The current source I1 is coupled to the read transfer capacitor C1 in parallel. The read transfer transistor M5 has a first end, a second end and a control end, wherein the first end is coupled to the pixel supply voltage level VDDPXL, and the control end is coupled to the second end of the source follower transistor M4 to receive the voltage Vpd. In this way, the output voltage Vout is generated at the second end of the read transfer transistor M5 and can be read out.

[0025] For the processing circuit 110, the area sizes of the transistors M1 and M2 in the current mirror circuit 1101 are respectively related to the size values ​​n and m, such as Figure 1 , as shown by the current mirror ratio "n:m" in . For example (but not limited to), the transistor M1 can be implemented by using n transistors connected in parallel, and the transistor M2 can be implemented by using m transistors connected in parallel. The current mirror circuit 1101 is used to generate a current mirror current (mirrored current) on the output node N3 as the reference current based on the current on the input node N2. For example, the current amount of the current mirror current on the output node N3 will be equal to the current amount of the current on the input node N2 multiplied by the value The values ​​of m and n are adjustable.

[0026] The switch unit SW1 is selectively coupled between the current mirror circuit 1101 (i.e., the node N2) and the node N1 of the processing circuit 110. The switch unit SW2 is selectively coupled between the pixel supply voltage level VDDPXL and the node N1 of the processing circuit 110. The switch unit SW3 is selectively coupled between a first end of the reference capacitor Csh and the output node N3 of the current mirror circuit 1101. The switch unit SW4 is selectively coupled between the first end of the reference capacitor Csh and the ground level GND. The reference capacitor Csh has the first end and a second end, and the second end is coupled to the ground level GND.

[0027] The comparator 1102 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is coupled to the first terminal of the reference capacitor Csh, the second input terminal is coupled to the threshold voltage Vth, and the output terminal is used to generate and output the output signal SH_OUT as a shutter output signal, and the shutter output signal is used to determine the length of the exposure time segment. The control circuit 115 included in the processing circuit 110 is used to generate four control signals SC, EN and To control the open / closed states of the switch units SW1, SW2, SW3 and SW4 respectively. is an inverted signal of the control signal SC, and the control signal It is an inverted signal of the control signal EN.

[0028] In practice, in this embodiment (but not limited to), the photodiode supply voltage levels VDDPD of all pixel units 106_1 to 106_N of the sensor array 105 are respectively coupled to the node N1. When all pixel units are exposed, the processing circuit 110 is used to generate the current mirror current according to the current amount of the photodiode currents of all pixel units caused by light irradiation (i.e., the sum of the photodiode currents of all pixel units), and then determine the length of the exposure time segment according to the current mirror current. It should be noted that in other embodiments, the processing circuit 110 can also generate the current mirror current according to a part of the photodiode current of one or more pixel units.

[0029] Figure 2 is a schematic diagram showing an example of the predicted length of the exposure time segment, the signal waveforms of the reset control signal RST, the voltage Vsh, the control signal EN and the output signal SH_OUT. Figure 2 As shown in FIG. 1 , before time point t1 , the reset control signal RST is at a high logic level, the control signal SC is also at a high logic level, and accordingly the control signal At this time, the switch unit SW1 is in a closed state, and the switch unit SW2 is in an open state, so that the photodiode supply voltage level VDDPD of each pixel unit 106_1 to 106_N is disconnected from the pixel supply voltage level VDDPXL. In addition, the control signal EN is in a low logic level, and the control signal At the high logic level, since the switch unit SW3 is in an open state and the switch unit SW4 is in a closed state, the current mirror circuit 1101 is disconnected from the comparator 1102 and the reference capacitor Csh, and the two voltage levels of the two terminals of the reference capacitor Csh are connected to the ground level GND. At this time, the current mirror circuit 1101 does not generate a current mirror current at the node N3.

[0030] At time point t1, the control signal EN switches from the low logic level to the high logic level, so that the switch unit SW3 is in a closed state and the switch unit SW4 is in an open state. The current mirror circuit 1101 starts to mirror the current on the node N2 according to the current mirror ratio to generate and output the current mirror current on the node N3. Since the current mirror current charges the reference capacitor Csh (i.e., a sampling / holding capacitor), the voltage level on the first end of the reference capacitor Csh, i.e., the sampling / holding voltage Vsh, gradually increases.

[0031] The comparator 1102 is used to compare the sample / hold voltage Vsh with the threshold voltage Vth to generate and output the output signal SH_OUT. When the sample / hold voltage Vsh is less than the threshold voltage Vth, the output signal SH_OUT is at a low logic level, and when the sample / hold voltage Vsh becomes greater than the threshold voltage Vth, the output signal SH_OUT is at a high logic level.

[0032] For example, at time point t2, the sample / hold voltage Vsh begins to become larger than the threshold voltage Vth, and a rising edge appears in the output signal SH_OUT. At time point t3, when the reset control signal RST is still maintained at a high logic level, it indicates that the execution of the reset charge operation has not ended, and the control signal SC is switched from a high logic level to a low logic level, so that the switch unit SW1 is in an open state, and the switch unit SW2 is in a closed state. At this time, the photodiode supply voltage level VDDPD of each pixel unit is connected to the pixel supply voltage level VDDPXL through the switch unit SW2. In addition, the control signal EN is also switched from a high logic level to a low logic level at time point t3, so that the switch unit SW3 is in an open state, and the switch unit SW4 is in a closed state. At this time, the charge on the first end of the reference capacitor Csh is discharged to the ground level GND, and the sample / hold voltage level Vsh is immediately reduced to zero, such as Figure 2 As shown in . Since the sample / hold voltage level Vsh is zero at time point t3, a falling edge appears in the output signal SH_OUT, causing the output signal SH_OUT to switch from a high logic level to a low logic level.

[0033] It should be noted that, in this embodiment, the predicted length of the shutter time is determined by the processing circuit based on the rising edge of the control signal EN and the rising edge of the output signal SH_OUT, such as Figure 2 As shown in . That is, the time end point of the predicted length of the exposure time segment is determined based on the time point at which the signal level of the shutter output signal SH_OUT changes. After obtaining the predicted length of the shutter time, the image sensor device enters a shutter mode (such as a global shutter mode or a rolling shutter mode) during the time segment between time points t4 and t5, wherein the length of the time segment is equal to the predicted length of the shutter time, or may also be determined by the predicted length of the shutter time.

[0034] According to the estimated or predicted exposure time segment, when within the estimated or predicted exposure time segment between time points t4 and t5, the voltage Vpd can be gradually reduced from the pixel supply voltage VDDPXL to a lower voltage level, and the charge amount corresponding to the voltage difference between the two voltages at time points t4 and t5 is the charge signal to be read.

[0035] Furthermore, in other embodiments, the current mirror ratio may also be adjusted.

[0036] Furthermore, in other embodiments, the current mirror circuit 1101 may be used to sample / hold and mirror the charging current of one or more pixel units among all pixel units 1601_1 to 1601_N to predict the length of the exposure time segment for one or more subsequent frames. Figure 3 FIG. 3 is a schematic diagram of an exemplary image sensor device 300 according to another embodiment of the present invention. Figure 3 As shown in FIG. 1 , the node N1 is only connected to the photodiode supply voltage level VDDPD in one or more pixel units, rather than being connected to all pixel units. Detailed description is omitted.

[0037] Furthermore, one or more spatial locations of one or more pixel units connected to the node N1 of the processing circuit 110 with the photodiode supply voltage level VDDPD may also be any spatial location within an entire frame / image; this is not a limitation of the present invention.

[0038] Furthermore, the prediction operation of estimating the appropriate exposure time segment for the next frame may also be performed within the exposure time segment of the previous or current frame and / or may also be performed at any time point between these two exposure time segments.

[0039] By doing so, the image sensor device can dynamically adjust the length of the exposure time segment according to the ambient light conditions, so that the image sensor device can be used and applied in different light conditions. In one embodiment, the appropriate exposure time segment for the next image frame can be correctly predicted based on only one previous image frame or one current image frame.

[0040] Furthermore, in other embodiments, an image sensor device may include a plurality of the aforementioned processing circuits, and the processing circuits are respectively related to a plurality of pixel units in the sensor array, or are related to all pixel units in the sensor array. Figure 4 FIG. 4 is a block diagram of an image sensor device 400 according to an embodiment of the present invention. Figure 4As shown in , the image sensor device 400 includes the sensor array 105, the control circuit 115, and M groups of processing circuits 110, wherein the value of M may be equal to or less than the value of N. In this embodiment, each processing circuit 110 is used to receive a plurality of different control signals from the control circuit 115. For example, if the values ​​of M and N are equal, it means that each processing circuit 110 is coupled to a corresponding pixel unit provided in the sensor array 105. At this time, each processing circuit 110 generates a current mirror current according to the current amount of the photodiode current of the corresponding pixel unit, wherein the current amount is generated by the light irradiation when the corresponding pixel unit is exposed, and then each processing circuit 110 can determine the length of the exposure time segment according to the current mirror current. In fact, a plurality of different pixel units may be exposed to different light irradiation (but not limited to), and the current amounts of the current mirror currents of the different pixel units may be different, and the lengths of the exposure time segments determined based on the different current amounts of the different current mirror currents may also be different. In this embodiment, the control circuit 115 can select a specific exposure time segment from the exposure time segments with different lengths as a final exposure time segment for one or more subsequent frames. For example, the selected specific exposure time segment can be an exposure time segment with a maximum length, a minimum length, a median length, or an average length, and the average length can be calculated from the different lengths. After determining the final exposure time segment, the control circuit 115 can also additionally fine-tune or correct the final exposure time segment.

[0041] In other embodiments, the value of M may be smaller than the value of N, that is, the number of the processing circuits may be less than the total number of all pixel units in the sensor array 105. In other words, each processing circuit is used to generate a current mirror current corresponding to a portion of the pixel units. Other descriptions are omitted.

[0042] The value of the current mirror ratio n:m, the capacitance of the reference capacitor Csh, and the voltage level of the threshold voltage Vth can be adjusted in different embodiments. For example, an initial level of the threshold voltage Vth can be set based on the full scale range of the analog-to-digital converter (ADC) in the comparator 1102. For example, when the full scale voltage is equal to 800 millivolts (but not limited), the initial level can be equal to 400 millivolts (but not limited). The level of the threshold voltage Vth can then be dynamically adjusted based on different light conditions.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An image sensor device, characterized in that: Include: A sensor array includes a plurality of pixel units, each pixel unit including a photodiode unit and a storage capacitor. When the image sensor device performs an exposure operation, the photodiode unit is illuminated to generate a photodiode current to generate an image of a specific frame. The photodiode current is stored in the storage capacitor; as well as a processing circuit coupled to the sensor array, for generating a reference current according to the photodiode current of the photodiode unit of the pixel unit before the exposure operation for generating the specific image frame begins, and then estimating the length of an exposure time segment for the exposure operation for generating the specific image frame based on the generated reference current; Wherein, the processing circuit includes a current gain circuit, which is configured to generate the reference current based on a current gain value of a portion or a sum of at least one photodiode current of at least one photodiode unit, and the processing circuit is configured to generate a shutter output signal for determining the length of the exposure time segment.

2. The image sensor device according to claim 1, wherein: The current gain circuit comprises: a current mirror circuit with a current mirror gain, having a first end and a second end, wherein the first end of the current mirror circuit is coupled to the pixel unit, and the second end of the current mirror circuit is coupled to a reference capacitor, and the current mirror circuit is used to generate the reference current based on the current mirror gain and a part of or all of the photodiode current of the photodiode unit; The processing circuit further comprises: The reference capacitor is coupled to the current mirror circuit and a ground level, and is used to be charged by the reference current; as well as A comparator having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal of the comparator is coupled to the second terminal of the current mirror circuit, the second input terminal of the comparator is coupled to a threshold voltage, and the output terminal of the comparator is used to generate a shutter output signal, and the shutter output signal is used to determine the length of the exposure time segment.

3. The image sensor device according to claim 2, wherein: The end time point of the length of the exposure time segment is determined based on the time point at which the signal level of the shutter output signal changes.

4. The image sensor device according to claim 2, wherein: The pixel unit further includes a first switch unit, which is coupled between a port corresponding to a first voltage level and a port corresponding to a second voltage level, the port corresponding to the first voltage level is coupled to a first end of a reset transistor of the pixel unit, the port corresponding to the second voltage level is coupled to a source follower transistor of the pixel unit, and the control end of the source follower transistor is coupled to a second end of the reset transistor; when the image sensor device estimates the length of the exposure time segment, the first switch unit will be in an open circuit state to separate the first voltage level from the second voltage level.

5. The image sensor device according to claim 4, characterized in that The processing circuit further includes a second switch unit, which is arranged between the first end of the current mirror circuit and the first end of the reset transistor of the pixel unit; when the image sensor device estimates the length of the exposure time segment, the second switch unit will be in a closed state so that the port corresponding to the first voltage level is connected to the current mirror circuit, and the reference current is generated from the second end of the current mirror circuit to charge the reference capacitor.

6. The image sensor device according to claim 5, characterized in that When the voltage at the first terminal of the reference capacitor increases and then becomes higher than the threshold voltage, the shutter output signal generated at the output terminal of the comparator may change in signal level.

7. The image sensor device according to claim 5, characterized in that The processing circuit further includes a third switch unit, which is coupled between the current mirror circuit and the reference capacitor; the starting time point of the length of the exposure time segment is determined when the third switch unit becomes a closed-circuit state so that the generated reference current charges the reference capacitor.

8. The image sensor device according to claim 7, characterized in that The processing circuit further includes a fourth switch unit, which is coupled between two ends of the reference capacitor. When the fourth switch unit is in a closed state, the charge energy on the reference capacitor will be cleared.

9. The image sensor device according to claim 2, wherein: The capacitance of the reference capacitor, the value of the current mirror gain and the level of the threshold voltage are all adjustable.

10. A method of an image sensor device, characterized in that: Include: Providing a sensor array, the sensor array comprising a pixel unit, the pixel unit comprising a photodiode unit and a storage capacitor; Using the sensor array to generate an image of a specific frame, when the image sensor device performs an exposure operation, the photodiode unit is illuminated to generate a photodiode current, and the photodiode current is stored in the storage capacitor; Before the exposure operation for the specific image frame begins to be performed, generating a reference current according to the photodiode current of the photodiode unit of the pixel unit; as well as estimating a length of an exposure time segment for the exposure operation of the specific image frame based on the generated reference current; The step of generating a reference current according to the photodiode current of the photodiode unit of the pixel unit comprises: generating the reference current according to a current gain value of a portion or a sum of at least one of the photodiode currents of at least one of the photodiode units using a current gain circuit; and A shutter output signal is generated for determining the length of the exposure time period.

11. The method according to claim 10, characterized in that The generating the reference current according to a current gain value of a part or a sum of at least one photodiode current of at least one photodiode unit using a current gain circuit further comprises: A current mirror circuit having a current mirror gain is used to generate the reference current based on the current mirror gain and a portion of or all of the photodiode current of the photodiode unit, wherein the current mirror circuit has a first end and a second end, wherein the first end of the current mirror circuit is coupled to the pixel unit, and the second end of the current mirror circuit is coupled to a reference capacitor.

12. The method according to claim 11, characterized in that The end time point of the length of the exposure time segment is determined based on the time point at which the signal level of the shutter output signal changes.

13. The method according to claim 11, characterized in that The pixel unit further includes a first switch unit, which is coupled between a port corresponding to a first voltage level and a port corresponding to a second voltage level, the port corresponding to the first voltage level is coupled to a first end of a reset transistor of the pixel unit, the port corresponding to the second voltage level is coupled to a source follower transistor of the pixel unit, and the control end of the source follower transistor is coupled to a second end of the reset transistor; when the image sensor device estimates the length of the exposure time segment, the first switch unit will be in an open circuit state to separate the first voltage level from the second voltage level.

14. The method according to claim 13, characterized in that A second switch unit is used, which is arranged between the first end of the current mirror circuit and the first end of the reset transistor of the pixel unit; when the image sensor device estimates the length of the exposure time segment, the second switch unit will be in a closed state so that the port corresponding to the first voltage level is connected to the current mirror circuit, and the reference current is generated from the second end of the current mirror circuit to charge the reference capacitor.

15. The method according to claim 14, characterized in that When the voltage at the first terminal of the reference capacitor increases and then becomes higher than the threshold voltage, the shutter output signal generated at the output terminal of the comparator will change in signal level.

16. The method according to claim 14, characterized in that A third switch unit is used, which is coupled between the current mirror circuit and the reference capacitor; the starting time point of the length of the exposure time segment is determined when the third switch unit becomes a closed-circuit state so that the generated reference current charges the reference capacitor.

17. The method according to claim 16, characterized in that A fourth switch unit is used, and the fourth switch unit is coupled between two ends of the reference capacitor. When the fourth switch unit is in a closed state, the charge energy on the reference capacitor will be cleared.

18. The method according to claim 11, characterized in that The capacitance of the reference capacitor, the value of the current mirror gain and the level of the threshold voltage are all adjustable.

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