Differential image sensor with long-term interruptible digital pixel storage

Abstract

The present invention relates to a differential image sensor, comprising a pixel arrangement and a plurality of acquisition circuits, the plurality of acquisition circuits corresponding to at least one pixel and forming a part of an integrated circuit. Each acquisition circuit comprises: at least one sensor circuit, which comprises a light sensor, the light sensor being configured to generate a sensor signal VSIG according to a light signal of the light sensor illuminating at least one pixel; at least one analog-to-digital conversion A / D circuit, which is configured to convert a current VSIG into a digital signal; at least one digital storage circuit, which is configured to store a representation of at least one digital signal corresponding to a previous VSIG; at least one digital comparison circuit, which is configured to compare the level of the stored representation with the current VSIG to detect whether there is a changed level; and at least one digital output circuit, which is configured to generate an event output under the condition that there is a changed level.

Description

Technical Field

[0001] The present invention relates to an image sensor comprising a plurality of pixel circuits. Background Art

[0002] As is known, image sensors have one ADC per pixel or per small subset of pixels. These image sensors are often used in applications where significant processing is performed in the pixel (e.g., X-ray particle tracking or satellite imaging).

[0003] In image sensors with a single slope ADC, it is known that each pixel includes a comparator, for example, from Reckleben et al. (2015), Suarez et al. (2010) and Chi et al. (2010). In particular, Suarez et al. create an analog ramp and a digital code globally for the pixel arrangement and provide the digital code to the pixel.

[0004] Image sensors that store digital values ​​inside the pixel and compare them between samples to create event change data are not known. The current invention enables an area optimized small pixel structure that can result in a high resolution and cost optimized sensor.

[0005] An image sensor is known from WO 2014 / 174498 Al in which a representation of the previous illumination level is digitally stored in the pixel and compared between samples to create event change data, while Itoh et al. proposed a conceptually related structure earlier in "4-Layer 3-D IC with a function of parallel signal processing" (Microelectronic engineering, Vol. 15, No. 1-4, 1991, pp. 187-190), which has a simple single-bit pixel compared to a fixed level.

[0006] Image sensors that use image pixel level change detection, storage, and comparison for event generation in the analog domain are known, for example, Chi et al., "CMOS Camera With In-Pixel Temporal Change Detection and ADC" (IEEE Journal of Solid-State Circuits, Vol. 42, No. 10, 2007, pp. 2187-2196). Comparison and storage in the analog domain offer advantages of digital methods (e.g., compact implementation) as well as disadvantages (e.g., gradual degradation of storage, including "hot-pixels", sensitivity to mismatch, reduced flexibility of light-to-electrical conversion functions).

[0007] Image sensors that share circuitry between pixels are well known, for example, KR2020-0029328A.

[0008] The use of stroboscopic effects is generally known, as well as suppressing harmonics by averaging or synchronizing during interfering (unwanted signal) periods, e.g. US 2015 / 358570 A1, where this technique is applied in a camera to detect and synchronize to a variable light source and then suppress the response to the light source.

[0009] WO 2020 / 080383 Al discloses an event-based dynamic vision sensor having a filter that ignores events from one pixel based on the event state (single bit) of neighboring pixels.

[0010] T. Delbruck in "Frame-free dynamic digital vision" (Proceedings of the International Conference on Secure Life Electronics, Advanced Electronics for Quality Life and Society, 2008, pp. 21-26) discloses filtering events from a dynamic vision sensor based on the timestamp of the last event of a pixel or the timestamps of neighboring pixels. This processing is implemented outside the pixel array and requires the events to be transmitted to the outside of the array in a computationally expensive manner (32-bit timestamp) for subsequent filtering.

[0011] EP 3313064 A1 discloses an analog storage dynamic vision sensor in which one comparator input is a representation of the previous value of pixel illumination, which is then used for subsequent comparisons. This can be thought of as analog feedback from the previous level to control the subsequent function of the analog comparator that is enabled (sampled) when creating a digital event output.

[0012] EP 2933995 A1 solves the problem of poor mismatch in standard analog storage implementations of dynamic vision sensors using transistors in subthreshold operation. Since operation in this transistor mode only works correctly over a limited range, they use global analog feedback to the analog part of the acquisition circuitry of the entire array to obtain satisfactory operation. Summary of the invention

[0013] There may be a need for a delta image sensor including improved pixel circuitry having digital storage of a representation of previous illumination intensity in a pixel.

[0014] This need is met by the subject matter of the independent claims. Advantageous embodiments are defined in the dependent claims.

[0015] The conception of the basic embodiment of the present invention can be explained as being based in particular on the following observations and perceptions:

[0016] CMOS (Complementary Metal Oxide Silicon) image sensors are mass produced in optimized foundry processes using specialized processes. CMOS digital logic devices are mass produced in optimized foundry processes. The density of both processes is increasing, especially the density of the logic process. The increased density allows for increased digital complexity associated with the pixel circuits in the image sensor.

[0017] Digital storage of previous levels in the pixel circuit has advantages in terms of storage fidelity and subsequent processing of the stored levels.

[0018] Local processing of the levels has efficiency advantages in terms of power and area since the propagation and processing of redundant data is limited.

[0019] The present invention discloses a structure and method in which digital conversion and storage are combined in the pixel circuit, along with local evaluation of differences that vary over time and location, and preparation and propagation of event information.

[0020] The invention is defined in the independent claim. The dependent claims describe preferred embodiments thereof.

[0021] The present invention relates to a differential image sensor, which includes a pixel arrangement and a plurality of acquisition circuits, which correspond to at least one pixel and form a part of an integrated circuit. Each acquisition circuit includes at least one sensor circuit, at least one analog-to-digital conversion circuit, at least one digital storage circuit, at least one digital comparison circuit and at least one digital output circuit, at least one sensor circuit includes a light sensor, the light sensor is configured to generate a sensor signal VSIG according to a light signal of the light sensor illuminating at least one pixel, and at least one analog-to-digital conversion circuit is configured to generate a digital representation corresponding to a current VSIG. At least one digital storage circuit is configured to store a representation of at least one previous VSIG. At least one digital comparison circuit is configured to compare the level of the stored representation with the current VSIG to detect whether there is a changed level. At least one digital output circuit is configured to generate an event output under the condition that there is a changed level.

[0022] Various embodiments may preferably achieve the following features:

[0023] Preferably, the time period between event generation is variable and / or is in the range of 0.1 seconds to 24 hours, preferably in the range of 0.2 seconds to 1 hour, more preferably 0.5 seconds to 60 seconds, and most preferably 1 to 5 seconds.

[0024] The analog-to-digital conversion circuit may include a comparator configured to compare VSIG to a swept frequency signal, wherein repetition of the swept frequency signal may be interrupted for a brief or extended period of time during operation, and / or wherein a repetition rate of the swept frequency signal is selected from one or more repetition rates corresponding to a light source modulation of a light signal illuminating the light sensor to preferably increase or suppress an event output.

[0025] Each acquisition circuit may be formed as an integrated circuit or part of an integrated circuit. The acquisition circuit may also be referred to as a pixel circuit throughout the specification. At least one sensor circuit may generate a sensor signal continuously or periodically. The analog-to-digital conversion circuit may convert the current VSIG into a digital signal. The digital storage circuit may be configured accordingly to store a representation of at least one digital signal corresponding to the previous VSIG. The digital representations of the current and previous VSIGs may be compared by at least one digital comparison circuit. The digital representations of the previous VSIG or VSIG may correspond to signals generated and stored in the digital storage circuit in any previous sampling cycle, respectively. It may also be a signal provided from the outside and stored as a reference signal. In addition, at least one event output line may be included in the circuit to output an event output from the differential image sensor. At least one event output line may also be shared by multiple digital output circuits.

[0026] Preferably, each acquisition circuit is shared between at least two pixels, wherein preferably the pixels are adjacent to each other.

[0027] Preferably, the sensor circuit is configured to generate VSIG based on one of the following relationships:

[0028] a) Linear dependence on light intensity,

[0029] b) a non-linear dependence on the light intensity, preferably a logarithmic dependence on the light intensity, and

[0030] c) a combination of nonlinear and linear dependence on light intensity,

[0031] Therein, preferably, the relationship is changeable in response to a control signal.

[0032] The control signal can be provided from outside the pixel array and acquisition circuitry. There can be one control signal for the entire array, or there can be more target signals.

[0033] Preferably, the sensor circuit is configured to change the dependence of VSIG on light intensity in response to a control signal during operation, preferably, the sensor circuit is configured to change the dependence of VSIG on light intensity irregularly in response to a control signal during operation, and / or the sensor circuit is configured to change the dependence of VSIG on light intensity in response to a control signal during operation individually for at least one pixel or a subset of pixels.

[0034] The control signal may be changed at irregular intervals due to changes in global light intensity or in the mode of operation. A separate circuit may be provided for generating the change in the control signal at irregular intervals.

[0035] The image sensor may preferably further implement the following features:

[0036] a) The analog-to-digital conversion circuit may include a comparator configured to compare VSIG with one of the following swept frequency signals:

[0037] aa) frequency swept analog input signal, and

[0038] ab) sequentially sweeping analog input signals, wherein each swept analog signal provides a different difference function,

[0039] Preferably, input signals are provided to a plurality of conversion circuits, and / or

[0040] b) the analog-to-digital conversion circuit may also be configured to provide at least one digital code synchronized with the swept frequency analog signal to at least one pixel,

[0041] ba) wherein, preferably, the digital code is a gray-coded digital signal, and

[0042] bb) wherein, preferably, the relationship between the analog swept frequency signal and the digital code is changed between a storage ramp and a comparison ramp.

[0043] also,

[0044] a) The sweep signal can be a linear ramp, or

[0045] b) The sweep signal can be a nonlinear ramp, or

[0046] c) the sweep frequency signal may be changed during operation, and / or

[0047] d) The period of the swept frequency signal can be changed during operation.

[0048] In particular, under item f) above, the repetition rate of the swept frequency signal can be selected from one or more repetition rates corresponding to the light source modulation of the light signal illuminating the light sensor, so as to preferably increase or suppress the response to the target, or to suppress the response to interference with a given frequency, the target being, for example, a light source with a given frequency.

[0049] Preferably, the image sensor further comprises at least one reference pixel configured to set sweep ramp limits, wherein preferably the at least one reference pixel is located outside the pixel arrangement and / or wherein preferably the at least one reference pixel is biased under reference conditions.

[0050] Preferably, the digital comparison circuit is configured to perform the comparison with the stored level during the frequency sweep of the analog signal, or the digital comparison circuit is configured to perform the comparison with the stored level after the frequency sweep of the analog signal.

[0051] “During the frequency sweep of the analog signal” and “during the frequency sweep of the analog signal” may represent the same process.

[0052] In particular, if the comparison is performed during the analog signal sweep, the A / D output value does not need to be stored, only the result of the comparison. This results in less memory requirements, but more comparisons are performed. If the comparison is performed after the analog signal sweep, the A / D output value needs to be stored. This increases the memory requirements, but reduces the number of comparisons required.

[0053] Preferably,

[0054] a) the digital comparison circuit is configured to use static logic in the pixel circuit to perform the comparison, or

[0055] b) the digital comparison circuit is configured to use dynamic logic in the pixel circuit to perform the comparison, and / or

[0056] c) the digital comparison circuit is configured to perform the comparison based on hysteresis, and / or

[0057] d) The digital comparison circuit is configured to perform comparison by acquiring a difference that changes from time to time in operation.

[0058] Preferably, the output circuit is configured to generate an output based on the comparison results of the comparison circuit in adjacent pixels, or the output circuit is configured to generate an output based on a function of adjacent pixels in a fixed configuration or in a configuration that changes during operation, wherein, preferably, the function is an average function, and / or the output circuit is configured to generate an output if the rate of change of the comparison results of the comparison exceeds a certain threshold.

[0059] Preferably,

[0060] a) the output circuit is configured to generate an output based on the output in the adjacent pixel, or

[0061] b) the output circuit is configured to generate an output based on the levels stored in adjacent pixels, or

[0062] c) The output circuit is configured to generate an output based on the plurality of stored values.

[0063] Preferably,

[0064] a) the output circuit is configured to generate an event output indicating the direction of the changing level, and / or

[0065] b) the output circuit is configured to generate an event output indicating a level changing in only one direction, and / or

[0066] c) the output circuit is configured to generate an event output indicating the magnitude of the changed level, and / or

[0067] d) The output circuit is configured to generate an event output indicative of the illumination intensity before and / or after the changed level.

[0068] Preferably,

[0069] a) digital storage circuitry configured to provide the stored digital representation at an output line of the pixel arrangement, and / or

[0070] b) digital storage circuitry configured to selectively provide the stored digital representation for pixels having an event output at an output line of the pixel arrangement, and / or

[0071] c) the digital storage circuit is configured to provide the stored digital representation at an output line using an event column line, and / or

[0072] d) digital storage circuitry configured to write the stored digital representation to the pixel, and / or

[0073] e) digital storage circuitry configured to write the stored digital representation from the data stream, and / or

[0074] f) wherein the digital storage circuit is configured to write the stored digital representation from the data stream as a stream of events.

[0075] A single or multiple output lines may be provided. Output lines may also be shared between output circuits. Output circuits may also be provided.

[0076] Additionally, the digital representation stored in the acquisition circuit can also be written to from outside the array. The previous output can be written back to the stored digital levels of the pixels to provide the circuit with a reference of changes. The circuit will then only report changes relative to the reference. Normal image data would represent all pixels. However, the event stream only includes changes, so there is less data. Therefore, writing back the event stream allows for lower data rates.

[0077] Preferably, the sensor circuit receives feedback from a digital storage circuit corresponding to the stored digital level, or the stored digital level of an adjacent pixel, and the sensor circuit is configured to generate VSIG based on the feedback. The A / D circuit may receive feedback from the stored digital level, or the stored digital level of an adjacent pixel, and may be configured to adjust the output signal based on the feedback.

[0078] Preferably, the sensor circuit is configured to provide VSIG, and / or the image sensor is constructed from a plurality of semiconductor layers, wherein each level is optimized for the function of the layer.

[0079] In particular, an analog representation or analog level of VSIG may be provided and read directly from a circuit or array.

[0080] Multiple groups of acquisition circuits can be connected to a common or multiple common event output lines.

[0081] A group of acquisition circuits may share at least one of the following circuit elements: (a) a digital output circuit, (b) a digital comparison circuit, (c) additionally, a digital storage circuit, (d) additionally, an analog-to-digital conversion circuit. The drawings are representative and do not exclude other combinations of shared elements.

[0082] The present disclosure may also include implementing analog-to-digital conversion using a comparator utilizing a swept analog signal and a digital code.

[0083] The present invention provides event generation on multi-silicon layer devices, which is not disclosed in the Itoh et al. document mentioned above.

[0084] In image sensor design, shared circuits between pixels in an image sensor (such as KR2020-0029328A) are critical to creating dense pixel arrays and high pixel resolution. The present invention uses digital storage and event calculation in a time-sequential manner, which is particularly suitable for sharing resources between pixels without degrading performance.

[0085] Further, the present invention extends the use of the technology disclosed in US 2015 / 358570 Al to dynamic vision sensors, where digital storage and processing with global timing is used, which is efficient and reducing the number of events generated has a significant impact on power consumption and subsequent processing.

[0086] The present invention enables in-pixel digital storage, and events can be selectively created based on the digital levels (multiple bits) stored in adjacent pixels. This specific configuration of selective filtering can be used to achieve the same results as the single-bit filtering disclosed in WO 2020 / 080383 Al.

[0087] Furthermore, compared to T. Delbruck et al. as described above, the present invention has an inherent time base due to the A / D conversion technology to reduce the complexity of time stamping and enables local, digital time filtering of events without further transmission.

[0088] The present invention modulates analog circuit parameters based on stored digital levels or event outputs, because such feedback is effectively implemented using switches under digital control (surface area), which is different from the above-mentioned disclosed EP 3313064 A1. Compared with the above-mentioned EP 2933995 A1, the present invention proposes a modulation of analog circuit parameters based on locally stored pixel digital levels or event outputs, because such feedback is effectively implemented using switches under digital control (surface area). This is different from EP2933995A1 in function (pixel local), implementation method (digital control) and purpose.

[0089] The present invention uses the advantages of digital in-pixel conversion and storage to achieve an area-optimized (small) pixel structure, which is used to make a high-resolution and cost-optimized sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] The present invention is further described with reference to the accompanying drawings.

[0091] Figures 1 to 3 Exemplary embodiments of the present invention are shown.

[0092] Figure 1 A first exemplary configuration of a differential image sensor according to the present invention is schematically shown.

[0093] Figure 2 (a)-(d) schematically show another exemplary configuration of a differential image sensor according to the present invention, wherein Figure 2 (a) shows the sharing of event generation circuits, Figure 2 (b) shows the sharing of the event generation circuit and the digital comparison circuit, Figure 2 (c) shows the sharing of the event generation circuit, the digital comparison circuit and the digital storage circuit, Figure 2 (d) shows the sharing of the event generation circuit, the digital comparison circuit, the digital storage circuit and the A / D conversion circuit.

[0094] Figure 3 An exemplary embodiment is shown in which the conversion from analog (VSIG) to digital representation is implemented using a comparator in the pixel circuit and an analog sweep signal applied to the pixel circuit.

[0095] In the accompanying drawings, the same reference numerals denote the same or similar components, and thus redundant descriptions will be omitted. DETAILED DESCRIPTION

[0096] Figure 1 A first exemplary configuration according to the present invention is schematically shown. A differential image sensor, also known as an image sensor, comprises a pixel arrangement and at least one acquisition circuit (1). The acquisition circuit (1) may also be referred to as a pixel circuit. These circuits form part of an integrated circuit. The acquisition circuit (1) of each pixel comprises at least one sensor circuit (11), at least one analog-to-digital conversion circuit (12, A / D converter), at least one digital storage circuit (13), at least one digital comparison circuit (14) and at least one digital output circuit (15), the sensor circuit (11) comprising a light sensor, the light sensor generating a sensor signal (VSIG) based on a light signal or illumination intensity of the light sensor illuminating at least one pixel. The digital conversion circuit (12) may be connected to the output of the sensor circuit (11). At least one digital storage circuit (13) is configured to store a representation of at least one digital signal corresponding to a previous VSIG. The digital storage circuit (13) may be connected to the output of the A / D converter (12). At least one digital comparison circuit (14) is configured to compare the level of the stored representation with the current VSIG to detect whether there is a changed level. A digital comparison circuit (14) may be connected to the output of the digital storage circuit (13) and the output of the A / D converter (12). At least one digital output circuit (15) or digital event generation circuit is configured to generate an event output in the presence of a changed level. The output circuit (15) may be connected to the output of the digital comparison circuit (14).

[0097] At least one event output line (16) may be included in the pixel circuit (1) or outside the pixel circuit (1) to output an event output from the differential image sensor. The at least one event output line (16) may also be shared by a plurality of digital output circuits (15).

[0098] The first exemplary pixel configuration is capable of detecting illumination intensity that changes within a certain interval. When a digital comparison circuit (14) detects a difference between the digital representation of the stored signal and the digital representation after the interval, and the difference meets a given criterion, an event is generated and the fact that a change has occurred is reported as event information at the output of the image sensor.

[0099] In a range of applications, digital storage of levels may be preferred because (i) the stored level does not degrade over time, (ii) the storage circuit (13) can be physically smaller, (iii) the value can be easily used in adjacent cells, and (iv) the value can be used more flexibly to implement combined functions with other pixels or previous values.

[0100] In another exemplary configuration, Figure 2 As shown in (a)-(d), parts of the pixel circuitry are shared between subsets of pixels. The shared components are then used in a time-sequential manner.

[0101] Figure 2 (a) shows the sharing of the event generation circuit (15), Figure 2 (b) shows the sharing of the event generation circuit (15) and the digital comparison circuit (14), Figure 2 (c) shows the sharing of the event generation circuit (15), the digital comparison circuit (14) and the digital storage circuit (13), Figure 2 (d) shows the sharing of the event generation circuit (15), the digital comparison circuit (14), the digital storage circuit (13) and the A / D conversion circuit (12).

[0102] Note that other sharing configurations are possible and the above list does not exclude these possibilities. Different functions may also be shared to varying degrees, such as 4 pixels sharing the A / D conversion circuit (12) and 16 pixels sharing the event generation circuit (15). Other configurations may also be advantageous.

[0103] An exemplary embodiment of the present invention converts the optical illumination intensity signal into an analog electrical signal with a linear relationship. This embodiment is advantageous at low light illumination levels, integrates the charge in photodiode mode, and uses commercial standard cells optimized for image capture applications.

[0104] Another exemplary embodiment of the present invention converts the optical illumination intensity signal into an analog electrical signal having a logarithmic relationship. This embodiment is advantageous for optical illumination signals with a high dynamic range because the output analog signal is not saturated in a wider illumination intensity range.

[0105] Another exemplary embodiment of the present invention uses a combination of linear and logarithmic functions, or a similar combination of nonlinear functions as the response curve. This embodiment is advantageous for achieving good low light performance and high dynamic range. The first embodiment uses a fixed configuration with a combination function.

[0106] Another exemplary embodiment allows configuration so that the response curve changes for all pixel arrangements during operation. This is preferably implemented depending on the global illumination conditions or the operating mode of the image sensor application.

[0107] Another embodiment allows configuration so that the response curve is changed independently for a subset of pixels during operation. This is preferably implemented according to the local lighting conditions or the focus of interest of the image sensor application.

[0108] In an exemplary embodiment, according to Figure 3 The conversion from analog (VSIG) to digital representation is performed using a comparator in the pixel circuit (1) and an analog sweep signal applied to the pixel circuit. Depending on the point at which the comparator output switches, the digital representation is copied to a digital storage circuit (13).

[0109] In a derivative embodiment, the analog frequency sweep signal is a linear ramp; in another embodiment, the analog frequency sweep signal is a non-linear ramp, such as an exponential ramp.

[0110] Since the swept signal can be generated centrally, the non-linear ramp implementation is advantageous because the additional complexity of the circuit only needs to be considered once on the device, thereby (i) saving area and (ii) providing matched functionality for all pixels.

[0111] In particular, modification of the slope may be used to compensate for non-idealities in the sensor circuit (11), or changes with temperature or other environmental conditions.

[0112] In particular, the modification may be implemented by analog or digital means.

[0113] In particular, the modification can be performed with reference to the test cells on the device.This embodiment is advantageous because the compensation for non-idealities reflected in the test cells is automatic.

[0114] In one exemplary embodiment, the same analog swept frequency ramp is applied to the entire pixel array simultaneously. In a derivative embodiment, different analog swept frequency ramps are applied to subsets of the array.

[0115] Using different ramps is advantageous in case the characteristics of the sensor circuit (11) vary across the pixel arrangement (either intentional cell change or due to process or optical configuration), such variations being compensated by providing different ramps.

[0116] In another embodiment, the analog swept frequency ramp is modified at irregular intervals during operation depending on the operating mode of the image sensor.

[0117] In an exemplary embodiment, the changing digital code is provided simultaneously with the analog ramp. The digital code stored in the digital storage circuit (13) is the value of the digital code when the comparator output switches. In a first embodiment, the code is a binary code.

[0118] In a derivative embodiment, the digital encoding is a Gray code. Gray code is advantageous because (i) no synchronization with digital storage is required because only one edge changes at a time and the encoding on both sides of the edge is valid, and (ii) Gray code has fewer edges in one cycle and consumes less power.

[0119] In a derivative embodiment, the analog and digital code sweeps are sequentially divided into a storage sweep and a comparison sweep, or multiple comparison sweeps. The relationship between the analog signal level and the digital code changes between the reference sweep and the comparison sweep. This is advantageous because the digital comparison logic required in the pixel is simpler. This can reduce the required area.

[0120] In derivative embodiments, different relationships between analog sweep levels and digital codes are created for different subsets of pixels.

[0121] This is advantageous because the digital code can be varied while being (i) calculated or (ii) timed using digital circuitry. This saves area when generating multiple analog ramps and provides flexibility so that the functionality of subsets of the pixel arrangement can be compensated or altered.

[0122] In an exemplary embodiment, a digital comparison between the stored level and the current level is continuously performed during the analog frequency sweep. The comparison result is related to the timing of the switching of the analog comparator output and the digital comparison. In this embodiment, the differentiation of the event generation threshold is implemented based on the relative timing.

[0123] In one exemplary embodiment, the change in timing is generated based on a clock. In another exemplary embodiment, the change is generated using a timer circuit within the pixel circuit.

[0124] In another exemplary embodiment, a digital comparison between the stored level and the current level is performed after the analog voltage sweep. This embodiment is advantageous in that the logic can use sequential elements, such as sequential bits (bitwise), again saving silicon area.

[0125] In one exemplary embodiment, sequential logic is implemented using static logic.

[0126] In another exemplary embodiment, sequential logic is implemented using dynamic logic.

[0127] In a derivative embodiment, the digital comparison is performed using feedback from previous results. This is often used to implement hysteresis in the comparison and is helpful in rejecting noise and reducing false events.

[0128] In a derivative embodiment, digital comparison and event generation is performed by taking the difference (>1) to generate an event. This may be advantageous to (i) reduce the number of events, or (ii) increase the resolution of event generation.

[0129] The acquired difference may depend on (i) signal level, (ii) operation mode, e.g. region of interest, (iii) adjacent pixel levels, (iv) previous level of the pixel, (v) previous event of the pixel, (vi) events of adjacent pixels.

[0130] In a derivative embodiment, event generation rates below a certain rate are suppressed within the pixel circuitry. This is advantageous because this information is less useful for subsequent image processing, and event suppression reduces power and processing requirements.

[0131] In one exemplary embodiment, the digital condition for event generation depends on event generation of neighboring pixel circuits. This operation can, for example, filter the events to reduce the number of false events.

[0132] In one exemplary embodiment, the digital condition for event generation depends on the stored levels of neighboring pixel circuits. This operation can, for example, filter events to increase sensitivity near edges.

[0133] In one exemplary embodiment, the digital condition for event generation depends on a plurality of stored levels of the pixel circuit. This operation can, for example, filter analog noise to reduce the number of false events.

[0134] In an exemplary embodiment, the sampling rate is selected to be synchronized with the flickering frequency of the interfering light source. This is advantageous because it allows events due to such light sources to be suppressed.

[0135] In an exemplary embodiment, the event output is a single event bit, such as an up event, a no event. In other words, an up event corresponds to an increased light intensity.

[0136] In another embodiment, the event output is two bits, such as up and down. In other words, the event output may indicate whether the light intensity or sensor signal VSIG is greater than or less than a stored light intensity level or a stored VSIG.

[0137] In another exemplary embodiment, the event output comprises a digital representation of the magnitude of the change.This embodiment is advantageous because it enables perfect reconstruction of the image from the event information.

[0138] Analog implementations of dynamic vision sensor cameras include analog storage of representations of previous pixel illumination intensities. This is typically sampled using a sample and hold circuit with a capacitor for storage. Any leakage in the circuit due to the capacitor itself or connected switches will cause degradation of the stored information. This degradation is not reflected in the data output and results in a loss of information.

[0139] Because of this loss of information, analog dynamic vision sensors typically require a refresh frame, where the image field is read out to restore a known state. This typically requires a high rate (tens of Hz).

[0140] This is not ideal because refreshing consumes power, interrupts operation (e.g., complicating object tracking), increases data rates, requires a second functional mode for the dynamic vision sensor array, which imposes area requirements and is generally not as high performance because it is not the primary function of the array, and is subject to the additional constraint that this secondary function must be aligned with the primary dynamic vision sensor function. The present invention provides a technique that does not require intermediate refresh frames or support circuitry in the array for the secondary function.

[0141] Digital storage does not degrade over time and information can be retained indefinitely without loss of information or the need to refresh image frames.

[0142] In certain applications such as surveillance, intelligent triggering of access points, there are often long periods of time where the image does not change, which allows a significant reduction in the observation rate and power savings. The digitally stored image does not degrade, allowing this interruption to be achieved without a refresh operation or refresh circuitry, potentially indefinitely, but typically only a few seconds.

[0143] In another exemplary embodiment, the event output includes a representation of the illumination intensity before and / or after the change. In one embodiment, the level of the value stored in the pixel array may be additionally read out.

[0144] In a derived embodiment, the digitally stored value is selectively read from the target area, ie by random reading.

[0145] In another exemplary embodiment, the digital levels are read via an existing common event output line. In one embodiment, the stored digital levels can be written to the arrangement of pixels to provide a new or intentionally modified reference for comparison. In a derivative embodiment, a data stream is written to the stored digital levels to intentionally provide a time-correlated reference for event generation.

[0146] In a related derivative embodiment, the data stream is an event stream similar to the event stream normally generated by the sensor.

[0147] In one embodiment, the sensor circuit (11) has feedback from a stored digital level, or feedback from a stored digital level of an adjacent pixel, to adjust the VSIG level of that pixel. This embodiment may be useful for implementing, for example, a hysteresis function in a minimal surface area.

[0148] In one exemplary embodiment, the comparator circuit has feedback from a stored digital level, or feedback from a stored digital level of an adjacent pixel, to adjust the function of the comparator, typically adding an offset. This embodiment can be advantageous in implementing, for example, a hysteresis function in a minimal surface area.

[0149] In an exemplary embodiment, the sampling rate is electronically configurable or electronically changed from time to time during operation.

[0150] The power consumption and event generation rate may depend on the sampling rate. Reducing the sampling rate enables very low power modes in quiescent conditions. In addition, the low sampling rate combined with integrating the behavior of the sensor circuit (11) enables operation in low light conditions.

[0151] In one exemplary embodiment, sampling is completely interrupted for an extended period of time.

[0152] The power consumption and event generation rate may depend on the sampling rate. Interrupting sampling for a period of time, such as 1 second, enables very low power operation, but preserves the fidelity of the recorded image due to digital storage.

[0153] In one exemplary embodiment, an analog signal level (VSIG) can be read out from the pixel arrangement. This embodiment can be implemented using a common event column line.

[0154] In one exemplary embodiment, an image sensor is constructed from multiple semiconductor layers, wherein the type of semiconductor process at each level is optimized for the function of the layer. This embodiment is advantageous because the optimization of the semiconductor process function allows for (i) improved performance, (ii) reduced silicon area and (ii) a) device size and (ii) b) device cost. The modified physical structure improves optical performance in terms of (i) fill factor (ii) quantum efficiency and reduces electrical interference between control signal lines and light sensor circuitry.

[0155] Multiple pixels are typically organized in a two-dimensional grid with "rows" and "columns." It should be noted that the definitions of "rows" and "columns" can be interchanged without affecting the present invention. It should also be noted that other geometric configurations that map to a two-dimensional grid are possible without affecting the applicability of the present invention.

[0156] Finally, it should be pointed out that the term "comprising" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. Elements described in connection with different embodiments may also be combined. It should also be noted that reference signs in the claims should not be interpreted as limiting the scope of the claims.

Claims

1. A differential image sensor, comprising a pixel arrangement and a plurality of acquisition circuits (1) corresponding to at least one pixel and forming part of an integrated circuit, each acquisition circuit (1) comprising: at least one sensor circuit (11) comprising a light sensor configured to generate a sensor signal VSIG based on a light signal of the light sensor illuminating the at least one pixel; at least one analog-to-digital conversion circuit (12) configured to generate a digital representation corresponding to a current VSIG; at least one digital storage circuit (13) configured to store a representation of at least one digital signal corresponding to a previous VSIG; at least one digital comparison circuit (14) configured to compare the stored represented level with the current VSIG to detect whether a changed level exists; as well as at least one digital output circuit (15) configured to generate an event output in the presence of a changed voltage level; The analog-to-digital conversion circuit (12) comprises a comparator, and the comparator is configured to compare the VSIG with a frequency sweep signal. wherein the repetition of the swept frequency signal can be interrupted for a brief or extended period of time during operation, and / or The repetition rate of the frequency sweep signal is selected from one or more repetition rates corresponding to the light source modulation of the light signal illuminating the light sensor, so as to increase or suppress event output.

2. The differential image sensor according to claim 1, wherein: The time period between event generation is variable and / or is in the range of 0.1 seconds to 24 hours.

3. The differential image sensor according to claim 1 or 2, wherein: Each acquisition circuit (1) is shared between at least two pixels, wherein the pixels are adjacent to each other.

4. The differential image sensor according to claim 1 or 2, wherein: The sensor circuit (11) is configured to generate VSIG based on one of the following relationships: a) Linear dependence on light intensity, b) a non-linear dependence on the light intensity, and c) a combination of a non-linear dependence and a linear dependence on said light intensity, Therein, the relationship can be changed in response to a control signal.

5. The differential image sensor according to claim 3, wherein: The sensor circuit (11) is configured to generate VSIG based on one of the following relationships: a) Linear dependence on light intensity, b) a non-linear dependence on the light intensity, and c) a combination of a non-linear dependence and a linear dependence on said light intensity, Therein, the relationship can be changed in response to a control signal.

6. The differential image sensor according to claim 1 or 2, wherein: The sensor circuit (11) is configured to change the dependence of VSIG on light intensity in response to a control signal during operation, and / or The sensor circuit (11) is configured to change the dependency of VSIG on the light intensity in response to a control signal during operation individually for at least one pixel or a subset of pixels.

7. The differential image sensor according to claim 3, wherein: The sensor circuit (11) is configured to change the dependence of VSIG on light intensity in response to a control signal during operation, and / or The sensor circuit (11) is configured to change the dependency of VSIG on the light intensity in response to a control signal during operation individually for at least one pixel or a subset of pixels.

8. The differential image sensor according to claim 4, wherein: The sensor circuit (11) is configured to change the dependence of VSIG on light intensity in response to a control signal during operation, and / or The sensor circuit (11) is configured to change the dependency of VSIG on the light intensity in response to a control signal during operation individually for at least one pixel or a subset of pixels.

9. The differential image sensor according to claim 5, wherein: The sensor circuit (11) is configured to change the dependence of VSIG on light intensity in response to a control signal during operation, and / or The sensor circuit (11) is configured to change the dependency of VSIG on the light intensity in response to a control signal during operation individually for at least one pixel or a subset of pixels.

10. The differential image sensor according to claim 1 or 2, a) Among them, The analog-to-digital conversion circuit (12) comprises the comparator, which is configured to compare VSIG with one of the following frequency sweep signals: aa) frequency swept analog input signal, and ab) sequentially sweeping analog input signals, wherein each swept analog input signal provides a different difference function, wherein the input signal is provided to a plurality of analog-to-digital conversion circuits (12), and / or b) wherein the analog-to-digital conversion circuit (12) is further configured to provide at least one digital code synchronized with the frequency-sweeping analog input signal to at least one pixel, ba) wherein the digital code is a Gray-coded digital signal, and bb) wherein the relationship between the swept analog input signal and the digital code changes between a storage ramp and a comparison ramp.

11. The differential image sensor according to claim 1 or 2, wherein: Each acquisition circuit (1) is shared between at least two pixels, wherein the pixels are adjacent to each other; a) wherein the analog-to-digital conversion circuit (12) comprises the comparator, and the comparator is configured to compare VSIG with one of the following frequency sweep signals: aa) frequency swept analog input signal, and ab) sequentially sweeping analog input signals, wherein each swept analog input signal provides a different difference function, wherein the input signal is provided to a plurality of analog-to-digital conversion circuits (12), and / or b) wherein the analog-to-digital conversion circuit (12) is further configured to provide at least one digital code synchronized with the frequency-sweeping analog input signal to at least one pixel, ba) wherein the digital code is a Gray-coded digital signal, and bb) wherein the relationship between the swept analog input signal and the digital code changes between a storage ramp and a comparison ramp.

12. The differential image sensor according to claim 1 or 2, wherein: The sensor circuit (11) is configured to generate VSIG based on one of the following relationships: a linear dependence on light intensity; a nonlinear dependence on the light intensity; and, a combination of a non-linear dependence and a linear dependence on said light intensity, wherein said relationship is changeable in response to a control signal; a) wherein the analog-to-digital conversion circuit (12) comprises the comparator, and the comparator is configured to compare VSIG with one of the following frequency sweep signals: aa) frequency swept analog input signal, and ab) sequentially sweeping analog input signals, wherein each swept analog input signal provides a different difference function, wherein the input signal is provided to a plurality of analog-to-digital conversion circuits (12), and / or b) wherein the analog-to-digital conversion circuit (12) is further configured to provide at least one digital code synchronized with the frequency-sweeping analog input signal to at least one pixel, ba) wherein the digital code is a Gray-coded digital signal, and bb) wherein the relationship between the swept analog input signal and the digital code changes between a storage ramp and a comparison ramp.

13. The differential image sensor according to claim 1 or 2, wherein: Each acquisition circuit (1) is shared between at least two pixels, wherein the pixels are adjacent to each other; wherein the sensor circuit (11) is configured to generate VSIG based on one of the following relationships: a linear dependence on light intensity; a nonlinear dependence on the light intensity; and a combination of a nonlinear dependence and a linear dependence on the light intensity, wherein the relationship is changeable in response to a control signal; a) wherein the analog-to-digital conversion circuit (12) comprises the comparator, and the comparator is configured to compare VSIG with one of the following frequency sweep signals: aa) frequency swept analog input signal, and ab) sequentially sweeping analog input signals, wherein each swept analog input signal provides a different difference function, wherein the input signal is provided to a plurality of analog-to-digital conversion circuits (12), and / or b) wherein the analog-to-digital conversion circuit (12) is further configured to provide at least one digital code synchronized with the frequency-sweeping analog input signal to at least one pixel, ba) wherein the digital code is a Gray-coded digital signal, and bb) wherein the relationship between the swept analog input signal and the digital code changes between a storage ramp and a comparison ramp.

14. The differential image sensor according to claim 1 or 2, wherein: The sensor circuit (11) is configured to change the dependence of VSIG on light intensity in response to a control signal during operation, and / or wherein the sensor circuit (11) is configured to change the dependency of VSIG on the light intensity in response to a control signal during operation for at least one pixel or a subset of pixels alone; a) wherein the analog-to-digital conversion circuit (12) comprises the comparator, and the comparator is configured to compare VSIG with one of the following frequency sweep signals: aa) frequency swept analog input signal, and ab) sequentially sweeping analog input signals, wherein each swept analog input signal provides a different difference function, wherein the input signal is provided to a plurality of analog-to-digital conversion circuits (12), and / or b) wherein the analog-to-digital conversion circuit (12) is further configured to provide at least one digital code synchronized with the frequency-sweeping analog input signal to at least one pixel, ba) wherein the digital code is a Gray-coded digital signal, and bb) wherein the relationship between the swept analog input signal and the digital code changes between a storage ramp and a comparison ramp.

15. The differential image sensor according to claim 1 or 2, wherein: Each acquisition circuit (1) is shared between at least two pixels, wherein the pixels are adjacent to each other; wherein the sensor circuit (11) is configured to change the dependence of VSIG on light intensity in response to a control signal during operation, and / or wherein the sensor circuit (11) is configured to change the dependency of VSIG on the light intensity in response to a control signal during operation for at least one pixel or a subset of pixels alone; a) wherein the analog-to-digital conversion circuit (12) comprises the comparator, and the comparator is configured to compare VSIG with one of the following frequency sweep signals: aa) frequency swept analog input signal, and ab) sequentially sweeping analog input signals, wherein each swept analog input signal provides a different difference function, wherein the input signal is provided to a plurality of analog-to-digital conversion circuits (12), and / or b) wherein the analog-to-digital conversion circuit (12) is further configured to provide at least one digital code synchronized with the frequency-sweeping analog input signal to at least one pixel, ba) wherein the digital code is a Gray-coded digital signal, and bb) wherein the relationship between the swept analog input signal and the digital code changes between a storage ramp and a comparison ramp.

16. The differential image sensor according to claim 1 or 2, wherein: The sensor circuit (11) is configured to generate VSIG based on one of the following relationships: a linear dependence on light intensity; a nonlinear dependence on the light intensity; and, a combination of a non-linear dependence and a linear dependence on said light intensity, wherein said relationship is changeable in response to a control signal; wherein the sensor circuit (11) is configured to change the dependence of VSIG on light intensity in response to a control signal during operation, and / or wherein the sensor circuit (11) is configured to change the dependency of VSIG on the light intensity in response to a control signal during operation for at least one pixel or a subset of pixels alone; a) wherein the analog-to-digital conversion circuit (12) comprises the comparator, and the comparator is configured to compare VSIG with one of the following frequency sweep signals: aa) frequency swept analog input signal, and ab) sequentially sweeping analog input signals, wherein each swept analog input signal provides a different difference function, wherein the input signal is provided to a plurality of analog-to-digital conversion circuits (12), and / or b) wherein the analog-to-digital conversion circuit (12) is further configured to provide at least one digital code synchronized with the frequency-sweeping analog input signal to at least one pixel, ba) wherein the digital code is a Gray-coded digital signal, and bb) wherein the relationship between the swept analog input signal and the digital code changes between a storage ramp and a comparison ramp.

17. The differential image sensor according to claim 1 or 2, wherein: Each acquisition circuit (1) is shared between at least two pixels, wherein the pixels are adjacent to each other; wherein the sensor circuit (11) is configured to generate VSIG based on one of the following relationships: a linear dependence on light intensity; a nonlinear dependence on the light intensity; and a combination of a nonlinear dependence and a linear dependence on the light intensity, wherein the relationship is changeable in response to a control signal; wherein the sensor circuit (11) is configured to change the dependence of VSIG on light intensity in response to a control signal during operation, and / or wherein the sensor circuit (11) is configured to change the dependency of VSIG on the light intensity in response to a control signal during operation for at least one pixel or a subset of pixels alone; a) wherein the analog-to-digital conversion circuit (12) comprises the comparator, and the comparator is configured to compare VSIG with one of the following frequency sweep signals: aa) frequency swept analog input signal, and ab) sequentially sweeping analog input signals, wherein each swept analog input signal provides a different difference function, wherein the input signal is provided to a plurality of analog-to-digital conversion circuits (12), and / or b) wherein the analog-to-digital conversion circuit (12) is further configured to provide at least one digital code synchronized with the frequency-sweeping analog input signal to at least one pixel, ba) wherein the digital code is a Gray-coded digital signal, and bb) wherein the relationship between the swept analog input signal and the digital code changes between a storage ramp and a comparison ramp.

18. The differential image sensor according to claim 10, a) wherein the frequency sweep signal is a linear ramp, or b) Among them, The frequency sweep signal is a nonlinear ramp, or c) Among them, The sweep signal varies during operation, and / or d) wherein the period of the frequency sweep signal varies during operation.

19. The differential image sensor according to claim 11, a) wherein the frequency sweep signal is a linear ramp, or b) Among them, The frequency sweep signal is a nonlinear ramp, or c) wherein the frequency sweep signal varies during operation, and / or d) wherein the period of the frequency sweep signal varies during operation.

20. The differential image sensor according to claim 12, a) wherein the frequency sweep signal is a linear ramp, or b) Among them, The frequency sweep signal is a nonlinear ramp, or c) Among them, The sweep signal varies during operation, and / or d) wherein the period of the frequency sweep signal varies during operation.

21. The differential image sensor according to claim 13, a) wherein the frequency sweep signal is a linear ramp, or b) Among them, The frequency sweep signal is a nonlinear ramp, or c) wherein the frequency sweep signal varies during operation, and / or d) wherein the period of the frequency sweep signal varies during operation.

22. The differential image sensor according to claim 14, a) wherein the frequency sweep signal is a linear ramp, or b) Among them, The frequency sweep signal is a nonlinear ramp, or c) Among them, The sweep signal varies during operation, and / or d) wherein the period of the frequency sweep signal varies during operation.

23. The differential image sensor according to claim 15, a) wherein the frequency sweep signal is a linear ramp, or b) Among them, The frequency sweep signal is a nonlinear ramp, or c) Among them, The sweep signal varies during operation, and / or d) wherein the period of the frequency sweep signal varies during operation.

24. The differential image sensor according to claim 16, a) wherein the frequency sweep signal is a linear ramp, or b) Among them, The frequency sweep signal is a nonlinear ramp, or c) wherein the frequency sweep signal varies during operation, and / or d) wherein the period of the frequency sweep signal varies during operation.

25. The differential image sensor according to claim 17, a) wherein the frequency sweep signal is a linear ramp, or b) Among them, The frequency sweep signal is a nonlinear ramp, or c) Among them, The sweep signal varies during operation, and / or d) wherein the period of the frequency sweep signal varies during operation.

26. The differential image sensor according to claim 10, wherein: The image sensor further includes at least one reference pixel configured to set sweep ramp limits, wherein the at least one reference pixel is located outside the pixel arrangement, and / or Wherein, the at least one reference pixel is biased under reference conditions.

27. The differential image sensor according to claim 11, wherein: The image sensor further includes at least one reference pixel configured to set sweep ramp limits, wherein the at least one reference pixel is located outside the pixel arrangement, and / or Wherein, the at least one reference pixel is biased under reference conditions.

28. The differential image sensor according to claim 17, wherein: The image sensor further includes at least one reference pixel configured to set sweep ramp limits, wherein the at least one reference pixel is located outside the pixel arrangement, and / or Wherein, the at least one reference pixel is biased under reference conditions.

29. The differential image sensor according to claim 18, wherein: The image sensor further includes at least one reference pixel configured to set sweep ramp limits, wherein the at least one reference pixel is located outside the pixel arrangement, and / or Wherein, the at least one reference pixel is biased under reference conditions.

30. The differential image sensor according to claim 19, wherein: The image sensor further includes at least one reference pixel configured to set sweep ramp limits, wherein the at least one reference pixel is located outside the pixel arrangement, and / or Wherein, the at least one reference pixel is biased under reference conditions.

31. The differential image sensor according to claim 20, wherein: The image sensor further includes at least one reference pixel configured to set sweep ramp limits, wherein the at least one reference pixel is located outside the pixel arrangement, and / or Wherein, the at least one reference pixel is biased under reference conditions.

32. The differential image sensor according to claim 10, wherein: The digital comparison circuit (14) is configured to perform a comparison with the stored level during a frequency sweep of the analog signal, or The digital comparison circuit (14) is configured to perform a comparison with the stored level after the analog input signal is frequency-sweeped.

33. The differential image sensor according to claim 11, wherein: The digital comparison circuit (14) is configured to perform a comparison with the stored level during a frequency sweep of the analog signal, or The digital comparison circuit (14) is configured to perform a comparison with the stored level after the analog input signal is frequency-sweeped.

34. The differential image sensor according to claim 17, wherein: The digital comparison circuit (14) is configured to perform a comparison with the stored level during a frequency sweep of the analog signal, or The digital comparison circuit (14) is configured to perform a comparison with the stored level after the analog input signal is frequency-sweeped.

35. The differential image sensor according to claim 18, wherein: The digital comparison circuit (14) is configured to perform a comparison with the stored level during a frequency sweep of the analog signal, or The digital comparison circuit (14) is configured to perform a comparison with the stored level after the analog input signal is frequency-sweeped.

36. The differential image sensor according to claim 19, wherein: The digital comparison circuit (14) is configured to perform a comparison with the stored level during a frequency sweep of the analog signal, or The digital comparison circuit (14) is configured to perform a comparison with the stored level after the analog input signal is frequency-sweeped.

37. The differential image sensor according to claim 20, wherein: The digital comparison circuit (14) is configured to perform a comparison with the stored level during a frequency sweep of the analog signal, or The digital comparison circuit (14) is configured to perform a comparison with the stored level after the analog input signal is frequency-sweeped.

38. The differential image sensor according to claim 26, wherein: The digital comparison circuit (14) is configured to perform a comparison with the stored level during a frequency sweep of the analog signal, or The digital comparison circuit (14) is configured to perform a comparison with the stored level after the analog input signal is frequency-sweeped.

39. The differential image sensor according to claim 31, wherein: The digital comparison circuit (14) is configured to perform a comparison with the stored level during a frequency sweep of the analog signal, or The digital comparison circuit (14) is configured to perform a comparison with the stored level after the analog input signal is frequency-sweeped.

40. The differential image sensor according to claim 1 or 2, a) wherein the digital comparison circuit (14) is configured to perform the comparison using static logic in the pixel circuit, or b) Among them, The digital comparison circuit (14) is configured to use dynamic logic in the pixel circuit to perform the comparison, and / or c) wherein the digital comparison circuit (14) is configured to perform the comparison based on hysteresis, and / or d) wherein the digital comparison circuit (14) is configured to perform the comparison by acquiring a difference that changes irregularly during operation.

41. The differential image sensor according to claim 1 or 2, wherein: The output circuit (15) is configured to generate an output according to the comparison result of the comparison circuit (14) in adjacent pixels, or wherein the output circuit (15) is configured to generate an output as a function of adjacent pixels in a fixed configuration or in a configuration that changes during operation, and / or Wherein, the output circuit (15) is configured to generate an output if the rate of change of the compared comparison result exceeds a certain threshold.

42. The differential image sensor according to claim 1 or 2, a) wherein the output circuit (15) is configured to generate an output based on outputs in adjacent pixels, or b) Among them, The output circuit (15) is configured to generate an output based on the levels stored in adjacent pixels, or c) wherein the output circuit (15) is configured to generate an output based on a plurality of stored values.

43. The differential image sensor according to claim 1 or 2, a) wherein the output circuit (15) is configured to generate an event output indicating the direction of the changed level, and / or b) Among them, The output circuit (15) is configured to generate an event output indicating a level changing in only one direction, and / or c) wherein the output circuit (15) is configured to generate an event output indicating the magnitude of the changed level, and / or d) wherein the output circuit (15) is configured to generate an event output indicative of the lighting intensity before and / or after the changed level.

44. The differential image sensor according to claim 1 or 2, a) wherein the digital storage circuit (13) is configured to provide the stored digital representation at an output line of the pixel arrangement, and / or b) Among them, The digital storage circuit (13) is configured to selectively provide the stored digital representation for pixels having an event output at an output line of the pixel arrangement, and / or c) wherein the digital storage circuit (13) is configured to provide the stored digital representation at the output line using an event column line, and / or d) wherein the digital storage circuit (13) is configured to write the stored digital representation into the pixel, and / or e) wherein the digital storage circuit (13) is configured to write the stored digital representation from the data stream, and / or f) wherein the digital storage circuit (13) is configured to write the stored digital representation from a data stream as an event stream.

45. The differential image sensor according to claim 1 or 2, wherein: The sensor circuit (11) receives feedback from the digital storage circuit (13) corresponding to the stored digital level, or corresponding to the stored digital level of an adjacent pixel, and the sensor circuit (11) is configured to generate VSIG based on the feedback, and / or The analog-to-digital conversion circuit (12) receives feedback from the stored digital level, or the stored digital level of an adjacent pixel, and is configured to adjust the output signal according to the feedback.

46. ​​The differential image sensor according to claim 1 or 2, wherein: The sensor circuit (11) is configured to provide an analog representation of VSIG, and / or The image sensor is composed of a plurality of semiconductor layers, wherein each level is optimized for the function of the plurality of semiconductor layers.

47. The differential image sensor according to claim 2, wherein: The time period is in the range of 0.2 seconds to 1 hour, or the time period is in the range of 0.5 seconds to 60 seconds, or the time period is in the range of 1 to 5 seconds.

48. The differential image sensor according to claim 4, wherein: The non-linear dependence is a logarithmic dependence.

49. The differential image sensor according to claim 6, wherein: The sensor circuit (11) is configured to vary the dependency of VSIG on light intensity at irregular intervals in response to a control signal during operation.

50. The differential image sensor according to claim 41, wherein: The function is an average function.

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