CN114173069A - Difference image sensor with digital pixel storage - Google Patents
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Abstract
The invention belongs to the technical field of image sensors, and particularly relates to a differential image sensor with digital pixel storage, which comprises a pixel array and a plurality of acquisition circuits, wherein each acquisition circuit comprises at least one sensor circuit and is used for generating a sensor signal VSIG according to an optical signal for illuminating at least one pixel corresponding to an optical sensor; at least one analog-to-digital conversion circuit for generating a current digital signal from the sensor signal VSIG; at least one digital storage circuit for storing a previous digital signal; at least one digital comparison circuit, which is used for comparing the level of the current digital signal with the level of the previous digital signal and judging whether the current digital signal has a changed level; and at least one digital output circuit, which generates and outputs an event signal when the current digital signal has a changed level.
Description
Technical Field
The invention belongs to the technical field of image sensors, and particularly relates to a differential image sensor with digital pixel storage.
Background
Image sensors having one ADC per pixel or per small subset of pixels are well known in the art and are commonly used in applications where important processing is performed in the pixels, such as X-ray particle trajectory tracking or satellite imaging.
Also, image sensors are known that generate events using image pixel level variation detection, storage and comparison in the analog domain, which provides advantages and disadvantages over digital methods, such as the possibility of implementation based on a compact architecture, and the gradual storage degradation, including "hot pixels", sensitivity to mismatch, reduced flexibility of the light-to-electricity conversion function, etc.
Image sensors that share circuitry between pixels are well known, for example, Suh et al have been proposed in 2020. Sharing is critical in image sensor design, creating dense pixel arrays and high pixel resolution based on shared implementations.
The CMOS image sensor is mass-produced in a professional process in an optimized process, and the CMOS digital logic device is mass-produced in an optimized process. The density of both processes is increasing, particularly digital logic processes, which allows for the addition of digital circuitry associated with the pixel circuitry in the image sensor. Furthermore, digital storage of a preceding stage in the pixel circuit has advantages in terms of fidelity of storage and subsequent processing of the storage stage.
Selanor goradona et al, solved the problem of mismatch in standard analog memory implementations of dynamic vision sensors using transistors in sub-threshold operation. Since operation in this transistor mode can only work properly to a limited extent, they use global analog feedback to the analog portion of the acquisition circuitry of the entire array to achieve satisfactory operation.
Disclosure of Invention
There may be a need for an improved delta image sensor with digital pixel storage, and in particular, there may be a need to use digital storage and event computation in a time sequential manner, which is particularly suitable for resource sharing between pixels without degrading performance. In particular, it may be desirable to modulate analog circuit parameters based on stored digital levels or event outputs, since this feedback is effectively accomplished by switches under digital control. In particular, modulation of analog circuit parameters based on locally stored pixel digital levels or event outputs may be required, since the feedback is effectively achieved with switches under digital control. In particular, small pixel structures that enable area optimization may be required, resulting in high resolution and cost optimized sensors. In particular, there may be a need for an improved incremental image sensor of pixel circuits with digital storage of representations of previous illumination intensities in the pixels. In particular, it may be desirable to achieve an area optimized small pixel structure, resulting in a high resolution and cost optimized sensor, taking advantage of the conversion and storage within digital pixels.
This need may be met by the subject matter of the independent claims. Advantageous embodiments are defined in the dependent claims.
One aspect of the invention relates to a delta image sensor with digital pixel storage, comprising a pixel array and a plurality of acquisition circuits, wherein the pixel array comprises a plurality of unit pixels, and each acquisition circuit corresponds to at least one unit pixel; wherein each of the acquisition circuits comprises:
at least one sensor circuit, each of said sensor circuits comprising a photosensor for generating a sensor signal VSIG from a light signal illuminating at least one pixel corresponding to said photosensor;
at least one analog-to-digital conversion circuit for generating a current digital signal from the sensor signal VSIG;
at least one digital storage circuit for storing a previous digital signal, wherein the previous digital signal is a digital signal generated from a previous sensor signal VSIG;
at least one digital comparison circuit, wherein the digital comparison circuit is used for comparing the level of the current digital signal with the level of the previous digital signal and judging whether the current digital signal has a changed level;
at least one digital output circuit, wherein the digital output circuit is used for generating and outputting an event signal when the current digital signal has a changed level.
In some embodiments, one acquisition circuit corresponds to at least two unit pixels adjacent to each other.
In some embodiments, the sensor circuit generates the sensor signal VSIG in response to a control signal, and the sensor signal VSIG changes its correspondence to light intensity based on control of the control signal, and/or,
the sensor circuit generates the sensor signal VSIG in response to a control signal during operation, and the sensor signal VSIG changes its correspondence to light intensity based on control of the control signal, wherein one of the control signals acts on the entire pixel array or on a local unit pixel in the pixel array.
In some embodiments, the sensor signal VSIG produced by the sensor circuit has any one of the following relationships to light intensity:
the sensor signal VSIG is linearly related to the light intensity, or,
the sensor signal VSIG is non-linearly related to light intensity, wherein the non-linear relationship includes, but is not limited to, logarithmic variation; or the like, or, alternatively,
the sensor signal VSIG is in a non-linear and linear correlation with light intensity; wherein, the above corresponding relation changes in response to a control signal.
In some embodiments, a) the analog-to-digital conversion circuit comprises a comparator for comparing the sensor signal VSIG with any one of the following scanning signals:
aa) an analog scan input signal;
bb) successive analog scan input signals, wherein each analog scan input signal provides a different ramp signal slope;
wherein a single or continuous analog scan input signal is used to provide to at least one of the analog-to-digital conversion circuits; and/or the presence of a gas in the gas,
b) the analog-to-digital conversion circuit is also used for providing at least one digital code in parallel with the scanning signal to at least one unit pixel, and the digital code comprises but is not limited to Gray code.
In some embodiments, the scan signal is a linear ramp, or,
the scanning signal is a non-linear ramp, or,
the scan signal changes during operation, and/or,
the period of the scanning signal varies during operation, and/or,
the scan signal is interrupted at a specific time during operation, the specific time being set or preset during operation.
In some embodiments, the display device further comprises at least one reference pixel for defining a ramp signal; wherein the reference pixel is disposed outside the pixel array.
In some embodiments, the digital comparison circuit compares levels of the previous digital signal during a scan of the analog signal; or the like, or, alternatively,
the digital comparison circuit compares the level of the previous digital signal after the scanning of the analog signal.
In some embodiments, the digital comparison circuit uses dynamic logic to perform the comparison of levels, or,
the digital comparison circuit uses static logic to make the comparison of levels.
In some embodiments, the digital output circuit is configured to output the output signal according to a comparison result of the digital comparison circuit in an adjacent pixel, or,
the digital output circuit is used to generate an output signal as a function of neighboring pixels in a fixed configuration or in a configuration that changes during operation, where the function includes, but is not limited to, an averaging function.
In some embodiments, the digital output circuit is configured to generate an event signal based on the output of a neighboring pixel, or,
the output circuit is used to generate an event signal according to the level stored in the adjacent pixel, or,
the output circuit is for generating an event signal from a plurality of pre-stored storage values.
In some embodiments, the digital output circuit is configured to generate an event signal indicative of a direction of a level change, and/or,
the digital output circuit is adapted to generate an event signal indicative of only one direction of change of one of the change levels, and/or,
the digital output circuit is operable to generate an event signal indicative of the magnitude of the change in level, and/or,
the digital output circuit is used to generate an intensity of light indicative of the level of the change before and/or after the change.
In some embodiments, the digital storage circuitry is used to provide a stored previous digital signal at an output line of the pixel array, and/or,
the digital storage circuit is used to selectively provide stored previous digital signals on output lines of the pixel array for unit pixels having event outputs, and/or,
the digital storage circuit is used to provide a stored previous digital signal at an output line using a time column line, and/or,
the digital storage circuit is used for writing the stored previous digital signal into the unit pixel, and/or,
the digital storage circuit is used for writing a data stream into a previous digital signal;
the digital storage circuit is used for writing data from a data stream as an event stream into a stored previous digital signal.
In some embodiments, the sensor circuit receives feedback from the digital storage circuit corresponding to the digital levels stored by the digital storage circuit or the digital levels stored by the adjacent pixels, and the sensor circuit generates a sensor signal VSIG based on the feedback card, and/or,
the analog-to-digital conversion circuit receives feedback from the level of the stored previous digital signal or the level of the stored previous digital signal of the adjacent unit pixel and adjusts the output current digital signal according to the feedback.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.
Fig. 1 is a block diagram of a circuit structure of a delta image sensor with digital pixel storage according to an embodiment of the present invention.
Wherein, in the figures, the respective reference numerals:
100. a sensor circuit; 200. an analog-to-digital conversion circuit; 300. a digital storage circuit; 400. a digital comparison circuit; 500. a digital output circuit.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are exemplary and intended to be illustrative of the embodiments of the present invention, and should not be construed as limiting the invention.
In the description of the embodiments of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience in describing the embodiments of the present invention and simplifying the description, but do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the embodiments of the present invention, "a plurality" means two or more unless specifically limited otherwise.
In the embodiments of the present invention, unless otherwise explicitly specified or limited, the terms "mounted," "connected," "fixed," and the like are to be construed broadly, e.g., as being fixedly connected, detachably connected, or integrated; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. Specific meanings of the above terms in the embodiments of the present invention can be understood by those of ordinary skill in the art according to specific situations.
In one embodiment of the present invention, as shown in fig. 1, a delta image sensor with digital pixel storage is provided, which includes a pixel array including a plurality of unit pixels and a plurality of acquisition circuits, each of which corresponds to at least one unit pixel, and is also referred to as a pixel circuit in the whole specification. Wherein each of the unit pixels is typically organized into a two-dimensional grid having "rows" and "columns" to form the pixel array. Alternatively, the unit pixels are arranged in an irregular shape to form the pixel array.
Each of the acquisition circuits includes a sensor circuit 100, an analog-to-digital conversion circuit 200, a digital storage circuit 300, a digital comparison circuit 400, and a digital output circuit 500, and at least one of the sensor circuit 100, the analog-to-digital conversion circuit 200, the digital storage circuit 300, the digital comparison circuit 400, and the digital output circuit 500 is provided.
The sensor circuits 100 each comprise a photo sensor for generating a sensor signal VSIG from a light signal illuminating at least one pixel corresponding to the photo sensor. The light sensor may generate the sensor signal VSIG continuously or periodically.
The analog-to-digital conversion circuit 200 is configured to generate a current digital signal from the sensor signal VSIG.
The digital storage circuit 300 is used for storing previous digital signals. Wherein the previous digital signal is a digital signal generated from a previous sensor signal VSIG. The previous sensor signal VSIG corresponds to a signal generated and stored in digital storage circuit 300 during any previous sampling period. Alternatively, the previous digital signal may be provided externally and stored. In order to guarantee the timeliness of data storage and to take into account that the level of the digital signal does not degrade with time, the previous digital signal is stored, and the storage circuit of the previous digital signal can be physically realized by a smaller volume, and the previous digital signal can be used more conveniently and more efficiently, such as combination and comparison with other pixels or other signals.
The digital comparison circuit 400 is used for comparing the level of the current digital signal with the level of the previous digital signal and determining whether the current digital signal has a changed level. The digital output circuit 500 is configured to generate and output an event signal when there is a changed level of the current digital signal.
The output mode of the event signal includes a continuous output mode and an intermittent output mode, and the output mode of the event signal is switched between the continuous output mode and the intermittent output mode in response to an interrupt control signal generated by the digital output circuit 500. By setting the continuous output mode, the method is applicable to the situation that the event signal is generated at high frequency, namely a high power consumption state. The intermittent output mode is suitable for a low power consumption state, that is, when the frequency of the event signal generation is not high, or it is understood that the event signal is not generated for a long time.
When the device is in the intermittent output mode, the event signal is intermittently output at preset specific time intervals. That is, the event signal is stored for a period of time, and after the event signal is stored for a period of time, the same event signal is output. Wherein, the specific time interval is set by itself, such as 5 minutes, 10 minutes or even half an hour, or 6 hours, etc., taking 5 minutes as an example, the event signal outputs an event signal every 5 minutes.
In this way, by using the intermittent output and the characteristic that the digital signal is easily stored in the digital output circuit 500 without data loss, low power consumption is ensured while lossless output of the event is ensured.
When in the continuous output mode, the event signal is output immediately when the current digital signal is detected to have a changed level.
In another embodiment of the present invention, when the digital output circuit 500 detects that there is a changed level of the current digital signal within a first specific time period and the frequency of the level change does not exceed a preset frequency, the digital output circuit 500 controls the output mode of the event signal to be an intermittent output mode. The first specific time period is set as needed, such as 1 minute. The preset frequency is preset, and when the frequency of the level change does not exceed the preset frequency, the generation frequency of the event signal is represented to be lower, so that the low power consumption mode, namely the intermittent output mode, can be set at the moment.
In another embodiment of the present invention, when the digital output circuit 500 detects that there is a changed level of the current digital signal in a first specific time period and the frequency of the level change exceeds a preset frequency, the frequency of the event signal generation is higher, and is a high power consumption mode, and the digital output circuit 500 controls the output mode of the event signal to be a continuous output mode.
In another embodiment of the present invention, when the digital storage circuit 300 does not acquire the digital signal generated according to the previous sensor signal VSIG within a second specific time period, it indicates that no new digital signal is generated within the second specific time period, and therefore it indicates that the external environment has not changed, that is, no new event signal is generated, and it can be determined that the digital storage circuit is in the low power consumption mode, and therefore a first command signal is generated and sent to the digital output circuit 500, and the digital output circuit 500 controls the output mode of the event signal to be the intermittent output mode according to the first command signal.
Further, when the digital storage circuit 300 obtains at least one digital signal generated according to the previous sensor signal VSIG within a second specific time period, which indicates that the external environment continuously changes, a second instruction signal is generated and sent to the digital output circuit 500, and the digital output circuit 500 controls the output mode of the event signal to be the continuous output mode according to the second instruction signal.
In addition, the storage of the digital signal does not degrade over time, the information can be retained indefinitely, the information is not lost or the image frame needs to be refreshed, in some application programs, such as monitoring, different triggering environments, the image is not changed for a long time, and the observation rate can be greatly reduced and the power can be saved by setting the switching of the event output mode.
The acquisition circuit is capable of detecting light intensity that changes over a period of time. If the digital comparison circuit 400 detects that there is a difference between the previously stored previous digital signal and the subsequent digital signal and the difference satisfies a predetermined criterion, an event is generated, i.e., an event signal is generated, and the fact of the change is reported as event information to a device, such as an image sensor, at the output terminal.
In another embodiment of the present invention, one of the acquisition circuits corresponds to at least two unit pixels, that is, one of the acquisition circuits can acquire signals of at least two unit pixels. Preferably, at least two unit pixels are adjacent to each other.
In another embodiment of the invention, as shown in fig. 1, the sensor circuit 100 generates the sensor signal VSIG in response to a control signal and the sensor signal VSIG changes its correspondence to the light intensity based on the control of the control signal, and/or the sensor circuit 100 generates the sensor signal VSIG in response to a control signal during operation and the sensor signal VSIG changes its correspondence to the light intensity based on the control of the control signal.
Wherein the control signal is applied to the entire pixel array or a local unit pixel in the pixel array. The operation period is a use period of the delta image sensor with digital pixel storage.
In another embodiment of the present invention, the sensor signal VSIG generated by the sensor circuit 100 has any one of the following relationships to light intensity:
the sensor signal VSIG is linearly related to the light intensity, or the sensor signal VSIG is non-linearly related to the light intensity, wherein the non-linear correlation includes, but is not limited to, logarithmic variation; or, the sensor signal VSIG exhibits a combined relationship of nonlinear and linear correlation with light intensity; wherein, the above corresponding relation changes in response to a control signal.
Wherein the sensor signal VSIG is linearly related to the light intensity, meaning that the optical illumination intensity signal is converted to an analog electrical signal (VSIG) having a linear relationship. The conversion relationship is suitable for application environments with low illumination and little illumination change.
The sensor signal VSIG is non-linearly related to light intensity, meaning that the optical illumination intensity signal is converted to an analog electrical signal having a logarithmic relationship. This conversion relationship is advantageous in terms of high dynamic range of the optical illumination signal, since the output analog signal does not saturate over a large range of illumination intensities to more truly reflect changes in the optical illumination intensity.
The sensor signal VSIG is a combination of non-linear and linear correlations of light intensity, meaning that the optical illumination intensity signal is converted to an analog electrical signal having a combination of logarithmic and linear relationships or a similar non-linear functional relationship.
During actual operation, the specific conversion correspondence is selected or set according to actual requirements.
Specifically, a signal source such as a signal generating circuit may be separately provided to supply the control signal, which is a signal that changes from time to time based on actual use. The variation of the control signal is derived from the global light intensity or the actual operation during operation. Based on the control signal, the conversion of the corresponding relation between the sensor signal VSIG and the light intensity is realized to meet the use requirements of different scenes on data.
In another embodiment of the present invention, as shown in fig. 1, the analog-to-digital conversion circuit 200 includes a comparator for comparing the sensor signal VSIG with a scan signal. Conversion from an analog signal (VSIG) to a digital signal is performed by the comparator and a scan signal applied to the pixel array. The digital representation is copied to the digital memory circuit 300 depending on the point at which the comparator output switches.
The scan signal may be an analog scan input signal, or a succession of analog scan input signals, each providing a different ramp signal slope. By providing different slope signal slopes, comparison between analog scanning input signals of different slope signal slopes and the sensor signal VSIG is achieved, and the accuracy of converting the sensor signal VSIG into a digital signal is improved.
Wherein a single or continuous analog scan input signal is used to provide to at least one of the analog-to-digital conversion circuits 200. That is, one scan signal may be swept to one or more analog-to-digital conversion circuits 200 in one acquisition circuit, or may be swept to one or more analog-to-digital conversion circuits 200 in a plurality of acquisition circuits at the same time, so as to improve the analog-to-digital conversion efficiency and the data processing speed.
And/or, b) the analog-to-digital conversion circuit 200 is further configured to provide a digital code in parallel with the scan signal to at least one pixel, and the digital code stored in the digital storage circuit 300 is a digital code value output after comparison by the comparator. The digital code is preferably a gray code, the gray code is fully utilized and does not need to be synchronous with digital storage, only one bit is changed at a time, the codes on any side of the gray code are effective, the gray code has fewer edges, and the power consumption in the data processing process is reduced.
In another embodiment of the present invention, the analog-to-digital conversion circuit 200 is a single slope analog-to-digital converter.
Wherein the analog-to-digital conversion circuit 200 compares the different storage ramps with the comparison ramp to implement the analog-to-digital conversion, the comparison of the storage ramp and the comparison ramp producing a difference function.
In another embodiment of the present invention, as shown in fig. 1, the analog-to-digital conversion circuit 200 includes a comparator for comparing the sensor signal VSIG with a scan signal. Conversion from an analog signal (VSIG) to a digital signal is performed by the comparator and a scan signal applied to the pixel array. The digital representation is copied to the digital memory circuit 300 depending on the point at which the comparator output switches.
The scan signal may be an analog scan input signal, or a continuous analog scan input signal, where each analog scan input signal provides a different slope of the ramp signal, and the slope of the ramp signal is a slope of the storage ramp.
By providing different slope signal slopes, comparison between analog scanning input signals of different slope signal slopes and the sensor signal VSIG is achieved, and the accuracy of converting the sensor signal VSIG into a digital signal is improved.
In another embodiment of the present invention, each comparison between the storage ramp and the comparison ramp generates a difference value therebetween, the difference value is a voltage difference, the voltage differences are summed to form a difference function, and the difference function is used to represent the difference between the storage ramp and the comparison ramp.
When the slope of the storage slope is set to be constant, if the slope of the comparison slope is also constant, a specific voltage difference exists between the storage slope and the comparison slope, and the specific voltage difference is constant. This applies to
When the slope of the storage slope is changed, the slope of the comparison slope is constant or changed, and when the slope of the slope is changed, the levels of the storage slope and the comparison slope are changed, at the moment, a specific voltage difference exists between the storage slope and the comparison slope, and the specific voltage difference changes along with the level change of the storage slope and the level change of the comparison slope.
In another embodiment of the present invention, the storage ramp is generated from a pre-stored digital signal generated by the digital storage circuit 300 for representing the light intensity at a previous time or a previous time period for the VSIG signal.
Then, the stored ramp is compared with a comparison ramp generated from the current VSIG signal at the current time to generate a digital signal when the light intensity signal changes.
Therefore, when the storage slope is derived from the previous moment, the slope of the storage slope is constant, and when the storage slope is derived from the previous time period, the slope of the storage slope is changed, so that the current analog-to-digital signal conversion is regulated and controlled based on the digital signal at the rear end, the conversion efficiency is improved, and meanwhile the generation of redundant events is reduced.
In another embodiment of the present invention, the storage slope is preset, and the slope of the slope is changed in real time, the change of the slope is based on a difference value generated by comparing the previous time with the comparison slope, and the difference value between the changed storage slope and the comparison slope is reduced by changing the slope of the slope, so as to change the difference function.
In another embodiment of the invention, the storage ramp and the comparison ramp are used according to the state of the pixel, wherein a change of state of the pixel reverses the definition of the storage ramp and the comparison ramp. That is, as the state of the pixel changes, the comparison slope at the current time is defined as the storage slope at the next time, so that the determination of whether the light intensity changes at the current time and the next time is realized.
If the digital code A is recorded during the storage slope, the digital code B is read during the comparison slope, and B is larger than or equal to A, the VSIG during the comparison is represented to be larger than the VSIG, namely, the change of the VSIG signal at the current moment and the change of the VSIG signal at the last moment are represented through the difference between the slopes, and then the change of the light intensity of the external environment is represented.
In another embodiment of the invention, a storage ramp is compared to one or more comparison ramps, depending on the state of the pixel.
Alternatively, the plurality of stored ramps are compared to one or more comparison ramps.
Wherein, a difference function is generated by comparing one storage slope with one comparison slope, and a difference function is generated when one storage slope is compared with a plurality of comparison slopes.
A plurality of storage ramps each generate a difference function when compared to a comparison ramp.
When the plurality of storage slopes are compared with the plurality of comparison slopes, a difference function is generated respectively.
In another embodiment of the invention, one storage ramp is compared to one or more comparison ramps, or a plurality of storage ramps are compared to one or more comparison ramps; wherein a comparison of a stored ramp and a compared ramp produces a difference function; also, the comparison between the storage ramp and the comparison ramp is not affected by the state of the pixel.
In another embodiment of the invention, a digital comparison based on a stored ramp and a compared ramp is performed during the ramp, and the digital comparison value produced by the digital comparison is not stored.
The ramp device is used for storing the time of the existence of the ramp and the comparison ramp, and only compares the time and does not store the comparison value temporarily so as to inhibit the signal change caused by the local light intensity change and reduce the generation of invalid events.
In another embodiment of the invention, a digital comparison based on the stored ramp and the comparison ramp is performed after the ramp period, and a digital comparison value generated by the digital comparison is stored.
In another embodiment of the present invention, the digital output circuit 500 is configured to generate and output an event signal when there is a changed level of the current digital signal and the changed level exceeds a preset specific threshold, wherein the specific threshold is set based on a fixed intensity change rate of the optical signal.
The light signal is a signal emitted by the artificial light source, the artificial light source usually has regularly changing intensity based on different voltages of the power supply, that is, the intensity of the artificial light source on the market regularly changes due to the limitations of the structure and control of the artificial light source, for example, the fixed intensity of an incandescent lamp changes to 14%, the fixed intensity of a fluorescent lamp changes to 8%, and the fixed intensity of an LED changes to 9%, and when the digital output circuit 500 generates an event signal and outputs a required specific threshold value which is set to be less than the fixed intensity change of the artificial light source, for example, 2% to 3%, the modulation of the artificial lighting easily causes a large number of redundant events.
Therefore, in order to suppress or eliminate redundant events caused by a fixed intensity variation of the artificial light source, it is therefore necessary to set the specific threshold value based on a fixed intensity variation rate of the light signal.
Specifically, when the number of the optical signals is one more, the specific threshold is greater than the fixed intensity change rate corresponding to the optical signal, so that the generation of redundant events is reduced.
When the optical signals are multiple and each optical signal has different fixed intensity change rates, the specific threshold is greater than the maximum fixed intensity change rate in the fixed intensity change rates, so that the influence of the fixed intensity change rates of all the optical signals per se is avoided. This arrangement is applicable to situations where the number of optical signals inherent in a known background environment and where all of the optical signals inherent in the background need to be shielded from causing redundant events.
If there are 3 inherent optical signals in the background environment of the experiment during the related experiment, in order to obtain the event change situation caused by the optical signals except for the 3 optical signals in the background environment, it is necessary to mask the redundant event caused by the 3 optical signals in the background environment during the experiment, so that the specific threshold is set to be greater than the maximum fixed intensity change rate of the 3 fixed intensity change rates corresponding to the 3 optical signals in the background environment, and the experiment requirement is also met.
In this case, the fixed intensity change rate of the optical signals other than the 3 optical signals in the background environment is larger than the specific threshold value. The setting of the specific threshold value is generally slightly larger than the maximum fixed intensity change rate of the 3 fixed intensity change rates corresponding to the 3 optical signals in the background environment, so that the acquisition of an event caused by the optical signal of the target is not influenced on the premise of shielding the redundant event generated by the optical signal in the background.
In a test case of the delta image sensor with digital pixel storage and synchronous sampling,
in another embodiment of the present invention, the specific threshold value may be set in advance or in real time according to a change in the optical signal during operation.
In another embodiment of the invention, the repetition rate of the scanning signal is predetermined and is used to reduce or eliminate redundant events due to variations in the intensity of the light signal illuminating the light sensor. Specifically, the repetition rate of the scan signal is the frequency at which the scan signal is provided to the analog-to-digital conversion circuit 200.
Wherein a repetition rate of the scanning signal is set based on at least one preset repetition rate that matches a modulation frequency of an optical signal illuminating the light sensor.
It is to be understood that the repetition rate of the scanning signal is selected from one or more preset repetition rates, each preset repetition rate corresponding to a modulation of the light source illuminating the light signal of the light sensor. It should be understood that, when the fixed intensity change rate of the optical signal itself is constant, the redundant events generated in a time period are constant, and in the time period, if the scanning signal continues to scan and the repetition rate is always higher than the modulation frequency of the optical signal irradiating the optical sensor, all the redundant events generated in the event period are acquired, so that in order to reduce the number of redundant events, the repetition rate of the scanning signal needs to be adjusted.
When the modulation frequency of the optical signal irradiating the optical sensor is plural, such as 50HZ, 100HZ, and 200HZ, that is, 50HZ, 100HZ, and 200HZ, respectively, the number of times of intensity changes of the corresponding light intensity in one cycle is 100 times, 200 times, and 400 times, respectively, the number of generated redundant events is 100, 200, and 400 times, respectively. At this time, in order to reduce the redundant events, the repetition rate of the scanning signal is set based on the repetition rates corresponding to 50HZ, 100HZ and 200HZ, for example, the repetition rate can be set to be smaller than the intensity change times of the light intensity, for example, the repetition rate of the scanning signal is set to be 25 times of scanning in one period, one redundant event is obtained by one scanning, 25 redundant events are obtained in total, and the reduction of the number of redundant events is realized.
Preferably, the repetition rate of the scanning signal is a multiple of the modulation frequency of the optical signal illuminating the light sensor.
In another embodiment of the present invention, the scan signal is a linear ramp, or a non-linear ramp including, but not limited to, an exponential ramp. The scanning signals can be generated in a centralized mode, and the scanning signals are preferably set to be nonlinear in consideration of the fact that most of the illumination intensity changes in a nonlinear mode, so that the scanning signals can be generated by a signal generating device on equipment, sharing of a hardware circuit is improved, and the size required by the hardware circuit is saved.
In another embodiment of the present invention, the scan signal is changed during operation, and/or a period of the scan signal is changed during operation, and/or the scan signal is interrupted at a specific time during operation, the specific time being set or preset during operation. During operation, the scanning signal of the linear ramp or the non-linear ramp can be changed to match different sensor signals VSIG, so as to implement real-time matching comparison.
In particular, the scan signal is repeatedly swept out during operation according to a preset scan rule, and the repetition of the scan signal can be interrupted or prolonged as required during operation to change the repetition rate of the scan.
In another embodiment of the present invention, as shown in fig. 1, the delta image sensor with digital pixel storage further comprises at least one reference pixel for defining a ramp signal. The reference pixels are preset or automatically set in real time during operation and are associated with the sensor signal VSIG. The reference pixel may be set after acquiring a specific value representation or value range representation of the sensor signal VSIG, and the reference pixel is used to define a ramp signal, thereby achieving more accurate and non-redundant contrast to more efficiently facilitate subsequent data generation.
In another embodiment of the present invention, the reference pixel is disposed outside the pixel array.
In another embodiment of the present invention, as shown in fig. 1, the digital comparison circuit 400 compares the level of the previous digital signal during the scanning of the analog signal; alternatively, the digital comparison circuit 400 compares the level of the previous digital signal after the scan of the analog signal.
When the digital comparison circuit 400 compares the level of the previous digital signal during the scanning of the analog signal, it is not necessary to store the a/D output value, but only the comparison result.
While in the process of comparison after scanning of the analog signal, an order, e.g., bitwise, may be used.
In another embodiment of the present invention, the digital comparison circuit 400 uses dynamic logic for the comparison of levels, or the digital comparison circuit 400 uses static logic for the comparison of levels.
When the comparison is performed in a state requiring low power consumption, static logic is selected to be used for the comparison of the levels. When the comparison speed is required to be fast, and the output result needs to be kept for a long time, the dynamic logic is selected to be used for comparing the level.
In another embodiment of the present invention, the digital comparison, i.e., the comparison of the next time instant to the previous time instant, is performed using feedback from the results of the previous comparison, thereby facilitating noise suppression and reduction of the generation of spurious events.
In another embodiment of the present invention, the comparison of the digital signals and the output of the event signals are performed in a manner that requires a specific difference to occur, thereby reducing the amount of time generated and increasing the resolution of the time generation. Wherein the specific difference is generated by a level of a signal, an operation mode, a level of an adjacent pixel, a previous level of the pixel, a previous generation time of the pixel, and an event generated by the adjacent pixel.
In another embodiment of the present invention, the digital output circuit 500 is used to output the output signal according to the comparison result of the digital comparison circuit 400 in the adjacent pixel, or the digital output circuit 500 is used to generate the output signal according to the function of the adjacent pixel in a fixed configuration or in a configuration that changes during operation, wherein the function includes but is not limited to an averaging function.
In another embodiment of the present invention, the digital output circuit 500 is used to generate an event signal based on the output of an adjacent pixel, or the output circuit is used to generate an event signal based on the level stored in an adjacent pixel, or the output circuit is used to generate an event signal based on a plurality of pre-stored values.
In another embodiment of the invention, as shown in fig. 1, the digital output circuit 500 is used to generate event signals indicating the direction of a level change, and/or the digital output circuit 500 is applied to generate one direction of change event signal indicating only one level change, and/or the digital output circuit 500 is used to generate event signals indicating the magnitude of a level change, and/or the digital output circuit 500 is used to generate a light intensity indicating a level change before and/or after a change.
In another embodiment of the invention, the generation of the event signal of one acquisition circuit is dependent on the event signal of another acquisition circuit that is adjacent, thereby filtering the events to reduce the number of spurious events. Alternatively, the generation of the event signal for one acquisition circuit is dependent on the stored digital levels of the adjacent other acquisition circuit, thereby filtering the events to provide greater sensitivity near the edges.
In another embodiment of the invention, the generation of the event signal for an acquisition circuit is dependent on a plurality of digital signals stored in a digital storage circuit 300 in the acquisition circuit.
In another embodiment of the invention, the increased light intensity is characterized when the output of the event signal is a single event bit, such as an up event. When the output of the event signal is two event bits, e.g., up and down, the event output may indicate whether the light intensity or pixel signal VSIG is greater or less than the stored light intensity level or stored VSIG. The event output also includes the amplitude of change of the digital signal, based on which the image can be perfectly reconstructed from the event information, thereby acquiring the currently detected image.
In another embodiment of the present invention, as shown in fig. 1, the digital storage circuit 300 is used for providing a stored previous digital signal at an output line of a pixel array, and/or the digital storage circuit 300 is used for selectively providing a stored previous digital signal for a unit pixel having an event output at an output line of a pixel array, and/or the digital storage circuit 300 is used for providing a stored previous digital signal at an output line using a time column line, and/or the digital storage circuit 300 is used for writing a stored previous digital signal to a unit pixel, and/or the digital storage circuit 300 is used for writing a data stream to a previous digital signal; the digital storage circuit 300 is used to write a stored previous digital signal from a data stream that is an event stream.
In another embodiment of the invention, the stored digital levels may be written into the pixel arrangement as a reference for comparison. While the data stream may be written to a stored digital level to intentionally provide a time-dependent reference for event generation. Wherein the stored digital level is the previous digital signal.
In another embodiment, the data stream is typically generated by a sensor.
The digital storage circuit 300 provides at least one output line and provides the at least one digital output circuit 500, so that one digital output circuit 500 or a plurality of digital output circuits 500 can share the output line.
The previous digital signal stored in the digital storage circuit 300 is written by an external pixel array, or a signal output at a previous time may be written into a stored previous digital signal, thereby characterizing the change process of the signal, for example, when the digital signal output at time t1 is p, at the next time t2, time t1 is the previous time, and the digital signal output at time t1 is p, then p is the previous digital signal at time t2, the previous digital signal is used as a reference, and only when the signal changes compared with the reference, that is, compared with time t1, at time t2, the event signal is output, that is, the signal is output only when the signal changes, thereby reducing the generation of redundant data.
In another embodiment of the invention, the digital storage values from the target area are selectively read, i.e. by random access.
In another embodiment of the invention, a sampling rate may also be set, the sampling rate being the frequency of acquisition generated for the event signal. The sampling rate may change from time to time in operation based on an electrical configuration, such as a hardware circuit. Different sampling rates also determine the difference between the power consumption and the event generation rate, and when no event signal or non-use time occurs for a long time, the extremely low power consumption mode can be realized by reducing the sampling rate, or the power consumption is reduced by completely interrupting the sampling for a period of time.
In another embodiment of the present invention, the sensor circuit 100 receives feedback from the digital storage circuit 300 corresponding to the digital level stored by the digital storage circuit 300 or the digital level of the adjacent pixel stored, and the sensor circuit 100 generates the sensor signal VSIG based on the feedback card, and/or the analog-to-digital conversion circuit 200 receives feedback from the level of the previous digital signal stored or the level of the previous digital signal stored by the adjacent unit pixel, and adjusts the current digital signal output according to the feedback. Through the setting of feedback, the generated sensor signal VSIG is more accurate.
In another embodiment of the present invention, the sensor circuit 100 is configured to provide an analog representation of the sensor signal VSIG and/or the delta image sensor with digital pixel storage is constructed from a plurality of semiconductor layers, each having a different optimization function.
In particular, the type of semiconductor process in each layer is optimized for the function of that layer. Such as for performance improvements, in particular for heat dissipation. Alternatively, the silicon area of the semiconductor layer may be reduced to meet the actual use requirements, following the requirements of device size and device cost, as long as the changed physical structure of the semiconductor layer can improve the accuracy and efficiency of the light intensity change and reduce the electrical interference between the control signal line and the photosensor circuit 100.
In another embodiment of the invention, each of the acquisition circuits may be connected to a common or a plurality of common event output lines. Any one of the digital output circuit 500, the digital comparison circuit 400, the digital storage circuit 300 and the analog-to-digital conversion circuit 200 can be shared by a group of acquisition circuits.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. A delta image sensor with digital pixel storage comprises a pixel array and a plurality of acquisition circuits, wherein the pixel array comprises a plurality of unit pixels, and each acquisition circuit corresponds to at least one unit pixel; wherein each of the acquisition circuits comprises:
at least one sensor circuit, each of said sensor circuits comprising a photosensor for generating a sensor signal VSIG from a light signal illuminating at least one pixel corresponding to said photosensor;
at least one analog-to-digital conversion circuit for generating a current digital signal from the sensor signal VSIG;
at least one digital storage circuit for storing a previous digital signal, wherein the previous digital signal is a digital signal generated from a previous sensor signal VSIG;
at least one digital comparison circuit, wherein the digital comparison circuit is used for comparing the level of the current digital signal with the level of the previous digital signal and judging whether the current digital signal has a changed level;
at least one digital output circuit, wherein the digital output circuit is used for generating and outputting an event signal when the current digital signal has a changed level;
the output mode of the event signal includes a continuous output mode and an intermittent output mode, the output mode of the event signal is switched between the continuous output mode and the intermittent output mode in response to an interrupt control signal, and the interrupt control signal is generated by the digital output circuit.
2. The delta image sensor with digital pixel storage according to claim 1, wherein when the digital output circuit detects that there is a level of change in the current digital signal within a first specific time period and the frequency of level change does not exceed a preset frequency, the digital output circuit controls an output mode of the event signal to be an intermittent output mode in which the event signal is intermittently output at a preset specific time interval.
3. The delta image sensor with digital pixel storage according to claim 1, wherein when the digital output circuit detects a changed level of the current digital signal within a first specific time period and a frequency of the level change exceeds a preset frequency, the digital output circuit controls an output mode of the event signal to be a continuous output mode in which the event signal is output immediately when the changed level of the current digital signal is detected.
4. The delta image sensor with digital pixel storage according to claim 1, wherein when the digital storage circuit does not acquire the digital signal generated from the previous sensor signal VSIG within a second specific time period, a first instruction signal is generated and sent to the digital output circuit, and the digital output circuit controls an output mode of the event signal to be an intermittent output mode in which the event signal is intermittently output at a preset specific time interval according to the first instruction signal.
5. The delta image sensor with digital pixel storage according to claim 1, wherein when the digital storage circuit obtains at least one digital signal generated according to a previous sensor signal VSIG within a second specific time period, a second instruction signal is generated and sent to the digital output circuit, and the digital output circuit controls an output mode of the event signal according to the second instruction signal to be a continuous output mode in which the event signal is output immediately when a changed level of the current digital signal is detected.
6. The delta image sensor with digital pixel storage of any of claims 2-5, wherein one acquisition circuit corresponds to at least two unit pixels adjacent to each other.
7. The delta image sensor with digital pixel storage according to any of claims 2-5,
the digital comparison circuit uses dynamic logic to perform a comparison of levels, or,
the digital comparison circuit uses static logic to make the comparison of levels.
8. The delta image sensor with digital pixel storage according to claim 7, wherein said digital output circuit is configured to output said output signal according to a comparison result of said digital comparison circuit in an adjacent pixel, or,
the digital output circuit is used to generate an output signal as a function of neighboring pixels in a fixed configuration or in a configuration that changes during operation, where the function includes, but is not limited to, an averaging function.
9. The delta image sensor with digital pixel storage of claim 8, wherein said digital output circuit is configured to generate an event signal based on an output of an adjacent pixel, or,
the output circuit is used to generate an event signal according to the level stored in the adjacent pixel, or,
the output circuit is for generating an event signal from a plurality of pre-stored storage values.
10. The delta image sensor with digital pixel storage according to claim 8, wherein said digital output circuit is configured to generate an event signal indicating a direction of a level change, and/or,
the digital output circuit is adapted to generate an event signal indicative of only one direction of change of one of the change levels, and/or,
the digital output circuit is operable to generate an event signal indicative of the magnitude of the change in level, and/or,
the digital output circuit is used to generate an intensity of light indicative of the level of the change before and/or after the change.
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