Gain controlled image sensor

Abstract

A gain-controlled solid-state imaging device, comprising a gain amplifier configured to amplify the output of photodiode, and circuitry configured to dynamically change the output of the amplifier during exposure in response to a feedback signal.

Description

[0001] GAIN CONTROLLED IMAGE SENSOR

[0002] TECHNICAL FIELD

[0003] The present disclosure generally pertains to image sensor technology, specifically focusing on the dynamic range and image processing capabilities relating to camera sensors and image data.

[0004] TECHNICAL BACKGROUND

[0005] Known are image sensors and their limitations in terms of dynamic range and acquisition time. Traditional image sensors consist of a photodiode, an amplifier and an integrating block that accumulate charges for a fixed amount of time (exposure time) and measure the light incident on the photodiode as a voltage signal.

[0006] In such a voltage measurement process the photodiode converts the incident light into an electrical charge. The amplifier then amplifies this charge to a measurable voltage level. The integrator accumulates the voltage level of the amplifier over a fixed amount of time, known as the exposure time. This integration process allows for the accumulation of a voltage level to obtain an analog voltage signal, which is proportional to the incident light intensity. Then an Analog-to-Digital-Converter ADC converts the analog voltage signal into a digital representation that can be further processed and analyzed. A sequencer controls the timing and synchronization of the voltage measurement process, ensuring accurate and precise data acquisition.

[0007] However, this fixed exposure time limits the dynamic range of the data.

[0008] Further known is an alternative solution, such as measuring the time it takes for the accumulation to reach a certain level.

[0009] There are two main approaches to time measurement: analog and digital. In the analog approach, the time measurement is achieved through the integration of two signals. An integrator accumulates the charges generated by the photodiode until the accumulated signal reaches a certain level. In parallel a second integrator integrates a constant to obtain a representation of time passed while the charges of the photodiode are accumulated. The time is obtained as the pixel signal when the accumulated signal reaches the certain level.

[0010] In the digital time measurement approach, a counter is used to count the number of clock cycles corresponding to the time passed while the charges of the photodiode are accumulated. Then the counter value is obtained as the pixel signal when the accumulated signal reaches the certain level. Although there exist such sensors and techniques for imaging, it is generally desirable to improve imaging.

[0011] SUMMARY

[0012] According to a first aspect, the disclosure provides a gain-controlled solid-state imaging device, comprising a gain amplifier configured to amplify the output of photodiode, circuitry configured to dynamically change the output of the amplifier during exposure in response to a feedback signal.

[0013] According to a second aspect, the disclosure provides a method for controlling a gain controlled solid-state imaging device, comprising amplifying, by a gain amplifier, the output of a photodiode, dynamically changing the output of the gain amplifier during exposure in response to a feedback signal.

[0014] According to a third aspect, the disclosure provides a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method above.

[0015] Further aspects are set forth in the dependent claims, the drawings and the following description.

[0016] BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Embodiments are explained by way of example with respect to the accompanying drawings, in which:

[0018] Fig. 1 is a schematic diagram of an imaging device, specifically designed for an image sensing application, such as a camera;

[0019] Fig. 2 is a diagram showing an example of an implementation of the imaging device of Fig. 1.

[0020] Fig. 3 is a flowchart of the operation of an imaging device of Fig. 1 and Fig. 2;

[0021] Fig. 4 is a schematic diagram of an imaging device, specifically designed for an image sensing application, such as a camera;

[0022] Fig. 5 is a diagram showing an example of an implementation of the imaging device of Fig. 4.

[0023] Fig. 6 is a flowchart of the operation of an imaging device of Fig. 4 and Fig. 5;

[0024] Fig. 7 is a schematic diagram of an imaging device, specifically designed for an image sensing application, such as a camera;

[0025] Fig. 8 is a diagram showing an example of an implementation of the imaging device of Fig. 7; Fig. 9 is a flowchart of the operation of an imaging device of Fig. 7 and Fig. 8;

[0026] Fig. 10 is a schematic diagram of a gain-controlled imaging device according to an embodiment of the present disclosure, specifically designed for an image sensing application, such as a camera;

[0027] Fig. 11 is a diagram showing an example of an implementation of the imaging device of Fig. 10;

[0028] Fig. 12 is a flowchart of the operation of an imaging device of Fig. 10 and Fig. 11;

[0029] Fig. 13 is a schematic diagram of a gain-controlled imaging device according to an embodiment of the present disclosure, specifically designed for an image sensing application, such as a camera;

[0030] Fig. 14 is a diagram showing an example of an implementation of the imaging device of Fig. 13;

[0031] Fig. 15 is a schematic diagram of a gain-controlled imaging device according to an embodiment of the present disclosure, specifically designed for an image sensing application, such as a camera;

[0032] Fig. 16 is a diagram showing an example of an implementation of the imaging device of Fig. 15;

[0033] Fig. 17 is a flowchart of the operation of an imaging device of Fig. 13 to Fig. 16;

[0034] Fig. 18a is a graph comparing a pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16;

[0035] Fig. 18b is a graph comparing an inverse pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16;

[0036] Fig. 18c is a graph comparing an inverse normalized pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16;

[0037] Fig. 19a is a graph comparing a pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16;

[0038] Fig. 19b is a graph comparing an inverse pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16;

[0039] Fig. 19c is a graph comparing an inverse normalized pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16;

[0040] Fig. 20a is graph comparing a pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16;

[0041] Fig. 20b is a graph comparing an inverse pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16;

[0042] Fig. 20c is graph comparing an inverse normalized pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16;

[0043] Fig. 21a depicts an image of an inside scene in the foreground and an outside scene in the background;

[0044] Fig. 21b depicts an image of an inside scene in the foreground and an outside scene in the background with a lower exposure time as the image of Fig. 21a;

[0045] Fig. 22a depicts an image of an inside scene and an outside scene with a lower exposure time of Fig. 21b;

[0046] Fig. 22b is a diagram depicting a measured signal level over time;

[0047] Fig. 23a is a diagram depicting a measured signal level over time;

[0048] Fig. 23b is a diagram depicting a measured signal level over time; Fig. 24 is a diagram depicting a derived signal over exposure time and the signal gradient of the measurement of Fig. 23a;

[0049] Fig. 25 a is a diagram of a gradient distribution of an image which may be used to correct the exposure of an image; and

[0050] Fig. 25b depicts an image of an inside scene in the foreground and an outside scene in the background;

[0051] DETAILED DESCRIPTION OF EMBODIMENTS

[0052] Before a detailed description of the embodiments under reference to Fig. 1 is given, general explanations are made.

[0053] Some embodiments provide accurate time measurement, which are not limited by long acquisition times or low resolution in certain conditions.

[0054] Some embodiments address the need for improved image sensors with controlled gain. Image sensors are an essential component in digital cameras, smartphones, surveillance systems, and other imaging devices. The dynamic range of an image sensor determines its ability to capture both bright and dark areas in a scene accurately. Traditional image sensors have limitations in their dynamic range, resulting in either overexposed or underexposed areas in an image of a scene with a high dynamic range.

[0055] Determine information may mean to establish, ascertain, identify, calculate or derive information.

[0056] To overcome this limitation, some embodiments have a gain-controlled image sensor. The core idea behind this invention is to dynamically adjust the gain of the photodiode (or the amplifier that amplifies the signal from the photodiode) in each pixel of the sensor. By doing so, the sensor can achieve a higher dynamic range and shorter acquisition time, leading to improved image quality.

[0057] Additionally, some embodiments include a method for deriving the gradient (intensity / time) per pixel, which allows for image manipulation techniques based on this information, such as changing an exposure time of some pixels in the image data simply by deriving the intensity based on the gradient and the changed exposure time. Storing the gradient instead of the intensity value per pixel is also proposed as a potential new standard for image acquisition and storage, which allows for exposure time based post-processing on the image data. In some embodiments a gain-controlled solid-state imaging device, comprises a gain amplifier configured to amplify the output of photodiode, and circuitry configured to dynamically change the output of the amplifier during exposure in response to a feedback signal.

[0058] The gain amplifier may be a component or circuitry that amplifies the output signal from the photodiode. It may be responsible for increasing the signal strength or gain before it is further processed or integrated by other components in the imaging device. The gain of the gain amplifier can be dynamically adjusted or controlled during the exposure process based on a feedback signal, allowing for changes in amplification to optimize the performance or dynamic range of the imaging device.

[0059] The photodiode may be a semiconductor device that converts light or photons into an electrical current. It is a key component of the solid-state imaging device and is responsible for capturing the incident light and generating an electrical signal proportional to the intensity of the light. The output of the photodiode is then amplified by the gain amplifier before further processing and integration by other components in the imaging device.

[0060] The electrical signal generated by a photodiode may be a voltage signal. When light falls on the photodiode, it creates the photocurrent, via a photovoltaic effect or photoelectric effect, which is directly proportional to the intensity of the incident light. This photocurrent is converted into a voltage signal using circuitry (e.g. a source follower) connected to the photodiode. The voltage output can then be further processed.

[0061] Dynamically changing the output of the amplifier may be a changing of the gain (amplification) of the amplifier or a modification of the output signal of the amplifier in real-time during the exposure process of the solid-state imaging device. The modification can be performed by circuitry provided after the amplifier (in particular directly after the amplifier). This changing of the output of the amplifier is done based on a feedback signal, which could be derived from various sources such as the integration output, the exposure time, or other factors related to the image acquisition process.

[0062] By dynamically changing the output of the amplifier, the device may optimize the amplification level to adapt to different lighting conditions or dynamic range requirements. This allows for better control over the signal strength and can help achieve a higher quality image with improved contrast and detail. The adjustment of the amplifier's output can be continuously or discretely varied based on the feedback signal received during the exposure process. In some embodiments the gain-controlled solid-state imaging device, comprises an integrator configured to integrate the dynamically changed output of the gain amplifier to obtain an integration output.

[0063] The integrator may be a component or circuitry that performs the task of integrating the dynamically changed output of the gain amplifier (e.g. until the integration output reaches a level of a predetermined reference signal and the exposure is ended). It accumulates the amplified signal from the gain amplifier and produces an integration output.

[0064] The purpose of the integrator in this solid-state imaging device may be to accumulate and combine the amplified signals from the gain amplifier to create a single output value that may represents the overall intensity or brightness of the captured pixel.

[0065] The integration output obtained from the integrator can be further processed or utilized for control of circuit that may sample a time measurement of the exposure time and thus end the exposure. The integration output may further be utilized for feedback to dynamically change the output of the amplifier. Various other purposes may be image manipulation, analysis, or storage. Thus, the integration output may be the accumulated or summed-up value of the dynamically changed amplified signal.

[0066] In some embodiments the circuitry is configured to dynamically change the input gain of the gain amplifier in response to the feedback signal.

[0067] The input gain may be the amplification of the signal received from the photodiode. The input gain may be changed by adjusting the resistance of a variable resistor connecting an input, that receives the electrical signal from the photodiode, and the output terminal of the amplifier. Dynamically changing the gain may result in a higher dynamic range and shorter acquisition time for the image device.

[0068] In this embodiment, the feedback signal may control the gain of the gain amplifier directly.

[0069] In some embodiments the circuitry comprises a controller configured to determine information indicative of a time passed since a beginning of exposure based on the integration output, determine the feedback signal based on the information indicative of a time passed since a beginning of exposure, and control the input gain of the gain amplifier based on the feedback signal.

[0070] The controller may be implemented as a component or circuitry. The controller can be implemented using various algorithms or methods, such as a PID controller or a digital-to-digital Delta-Sigma modulator. It provides the feedback signal for dynamically changing the gain of the amplifier. Thus, a faster convergence of the accumulation to the desired target may be achieved, thereby enabling high dynamic range imaging (time measurements) with shorter acquisition time.

[0071] The information indicative of a time passed since a beginning of exposure may be data or measurement that represents the duration of time that has elapsed since the start of the exposure process. This information may be derived from the integration output of the pixel, which accumulates charges generated by the photodiode over a fixed amount of time (exposure time). The controller analyzes this information to determine how much time has passed since the beginning of exposure, and then uses this data to calculate the appropriate feedback signal. The feedback signal, in turn, is utilized to adjust the input gain of the gain amplifier, facilitating dynamic control over the image device’s response to varying light conditions.

[0072] In some embodiments the gain-controlled solid-state imaging device comprises a comparison circuit configured to compare the integration output with a predetermined reference signal to obtain a comparison result indicative of whether the integration output has reached a signal level of the reference signal, and the controller configured to determine information indicative of a time passed since a beginning of exposure based on the comparison result.

[0073] The comparison circuit is a component of the gain-controlled solid-state imaging device that is responsible for comparing the integration output of the integrator with a predetermined reference signal. The purpose of this comparison is to determine whether the integration output has reached a signal level that corresponds to the reference signal. The comparison circuit may be a comparator or a circuit that calculates a difference. The comparison circuit then outputs a comparison result, which indicates whether the integration output has reached the reference signal or not. This comparison result is then used by the controller to determine the time that has passed since the beginning of exposure.

[0074] In some embodiments the controller comprises a second integrator configured to integrate the comparison result and to output an integration result as the information indicative of a time passed from a beginning of an exposure.

[0075] The second integrator that is part of the controller may be used to integrate the comparison result (which is based on the integration output) and provide an integration result that is information indicative of the time passed since the beginning of the exposure. For this second integration the comparison result may be signal with a high voltage level when the integration output has not reached a signal level that corresponds to the reference signal and a low or zero voltage level otherwise. This high or low voltage signal can serve as an integration constant for an integrator comprised in the controller thus deriving information indicative of the time that has passed since the beginning of exposure.

[0076] In some embodiments the gain-controlled solid-state imaging device comprises a sample circuit configured to sample the information indicative of a time passed since a beginning of exposure when the comparison result indicates that the integration output has reached a signal level of the reference signal.

[0077] The sample circuit is a circuit or component is responsible for sampling the information indicative of the time passed since the beginning of exposure. It samples this information when the comparison result indicates that the integration output has reached a signal level of the reference signal. Thus, the sample circuit captures the time information at the specific point when the desired level of accumulation has been achieved and the exposure is ended.

[0078] In some embodiments the gain-controlled solid-state imaging device is configured to determine a signal gradient based on the sampled the information indicative of a time passed since a beginning of exposure and the predetermined reference and store the signal gradient as a pixel value.

[0079] The signal gradient refers to the rate of change of the signal intensity over time. It represents how quickly the intensity of the signal is changing and thus how much light is received by the photodiode. The reference signal may be a predetermined signal level that is used to end the exposure and sample the information indicative of a time passed since a beginning of exposure when the integration output is equal to the reference signal. Thus, both the integration output and the information indicative of a time passed since a beginning of exposure are known at time of sampling and the gradient is determined.

[0080] In some embodiments the circuitry comprises a digital-to-analogue converter configured to receive the output of the gain amplifier and configured to provide an analogue signal to the integrator, wherein the digital-to-analog converter is controlled based on the feedback signal.

[0081] The digital-to-analog converter (DAC) may comprise a reference voltage input Vref and a digital input Din. Based on the inputs the DAC generates an output voltage Vout according to the formula Vout = Vref*(Din / Dmax), where Dmaxrepresents the maximum digital value. For instance, in an 8- bit system, Dmax would be equal to 255. In uses of DACs the reference voltage input Vref is typically constant. However, in this case, it may vary as the amplifier output signal may be used as Vref. The Dm signal is a digital signal that may be derived from the feedback signal. In configuration according to the embodiment, the DAC functions as a digital attenuator of the amplifier output signal. Thus, the DAC facilitates the attenuation of the analog amplifier output signal by a factor of Din / D max.

[0082] In some embodiments the gain-controlled solid-state imaging device comprises a comparison circuit configured to compare the integration output with a predetermined reference signal to obtain a comparison result indicative of whether the integration output has reached a signal level of the reference signal.

[0083] The comparison circuit is a component or circuit that compares the integration output (the accumulated charges generated by the photodiode) with a predetermined reference signal. The purpose of this comparison is to determine whether the integration output has reached a signal level that corresponds to the reference signal. The comparison circuit may be a comparator or a circuit that calculates a difference. The comparison circuit then outputs a comparison result, which indicates whether the integration output has reached the reference signal or not. This comparison result controls a sample circuit to sample information indicative of a time passed since a beginning of exposure from a controller.

[0084] In some embodiments the circuitry comprises a controller configured to determine information indicative of a time passed since a beginning of exposure, determine the feedback signal based on the information indicative of a time passed since a beginning of exposure, and control the digital-to-analogue converter based on the feedback signal.

[0085] The controller is the part of the image device that manages the dynamic change of the amplifier output by controlling the threshold based on the feedback signal in the digital to analog converter as described above.

[0086] In some embodiments the controller is configured to determine information indicative of a time passed since a beginning of exposure based on an oscillating signal provide by an oscillator.

[0087] The controller may comprise a counter in communication connection with the oscillator that counts the oscillations of the oscillating signal to determine information indicative of a time passed since a beginning of exposure.

[0088] In some embodiments the gain-controlled solid-state imaging device comprises sample circuit configured to sample the information indicative of a time passed since a beginning of exposure when the comparison result indicates that the integration output has reached a signal level of the reference signal. The sample circuit is a circuit or component is responsible for sampling the information indicative of the time passed since the beginning of exposure. It samples this information when the comparison result indicates that the integration output has reached a signal level of the reference signal. Thus, the sample circuit captures the time information at the specific point when the desired level of accumulation has been achieved and the exposure is ended.

[0089] In some embodiments the gain-controlled solid-state imaging device is configured to determine a signal gradient based on the sampled the information indicative of a time passed since a beginning of exposure and the predetermined reference and store the signal gradient as a pixel value.

[0090] The signal gradient refers to the rate of change of the signal intensity over time. It represents how quickly the intensity of the signal is changing and thus how much light is received by the photodiode. The reference signal may be a predetermined signal level that is used to end the exposure and sample the information indicative of a time passed since a beginning of exposure when the integration output is equal to the reference signal. Thus, both the integration output and the information indicative of a time passed since a beginning of exposure are known at time of sampling and the gradient is determined.

[0091] In some embodiments the circuitry comprises a pulse width modulator configured to receive the output of the gain amplifier and configured to provide a pulse width modulated signal to the integrator, wherein the pulse width modulator is controlled based on the feedback signal.

[0092] The pulse width modulator (PWM) is a device or circuit that generates a signal (high or low voltage level) with a fixed frequency, but the duty cycle (the ratio of high to low time) of the signal is varied to achieve a desired output. The high signal of the duty cycle may be the voltage level of the amplifier output signal and the low voltage level may be zero volts. In the embodiment, the PWM is used to modulate the output signal of the gain amplifier based on the feedback signal, wherein the modulated signal is provided to the integrator for integration. This modulation may be an on and off switching of the amplifier output signal using the amplifier output signal as a high voltage and zero volts as the low voltage of the duty cycle. By adjusting the duty cycle of the PWM signal based on the feedback signal, the output signal of the gain amplifier can be dynamically changed. The integrator following the PWM may then receive the high / low duty cycle signal only integration the high signal. Thus the duty cycle may lead to an attenuated integration output. In some embodiments the gain-controlled solid-state imaging device comprises a comparison circuit configured to compare the integration output with a predetermined reference signal to obtain a comparison result indicative of whether the integration output has reached a signal level of the reference signal.

[0093] The comparison circuit is a component or circuit that compares the integration output (the accumulated charges generated by the photodiode) with a predetermined reference signal. The purpose of this comparison is to determine whether the integration output has reached a signal level that corresponds to the reference signal. The comparison circuit may be a comparator or a circuit that calculates a difference. The comparison circuit then outputs a comparison result, which indicates whether the integration output has reached the reference signal or not. This comparison result controls a sample circuit to sample information indicative of a time passed since a beginning of exposure from a controller.

[0094] In some embodiments the circuitry comprises a controller configured to determine information indicative of a time passed since a beginning of exposure, determine the feedback signal based on the information indicative of a time passed since a beginning of exposure, and control the pulse width modulator based on the feedback signal.

[0095] The controller is the part of the image device that manages the dynamic change of the amplifier output by controlling the pulse width modulator based on the feedback signal as described above.

[0096] In some embodiments the controller is configured to determine information indicative of a time passed since a beginning of exposure based on an oscillating signal provide by an oscillator.

[0097] The controller may comprise a counter in communication connection with the oscillator and that that counts the oscillations of the oscillating signal to determine information indicative of a time passed since a beginning of exposure.

[0098] In some embodiments the gain-controlled solid-state imaging device comprises a sample circuit configured to sample the information indicative of a time passed since a beginning of exposure when the comparison result indicates that the integration output has reached a signal level of the reference signal.

[0099] The sample circuit is a circuit or component is responsible for sampling the information indicative of the time passed since the beginning of exposure. It samples this information when the comparison result indicates that the integration output has reached a signal level of the reference signal. Thus, the sample circuit captures the time information at the specific point when the desired level of accumulation has been achieved and the exposure is ended. In some embodiments the gain-controlled solid-state imaging device is configured to determine a signal gradient based on the sampled the information indicative of a time passed since a beginning of exposure and the predetermined reference and store the signal gradient as a pixel value.

[0100] The signal gradient refers to the rate of change of the signal intensity over time. It represents how quickly the intensity of the signal is changing and thus how much light is received by the photodiode. The reference signal may be a predetermined signal level that is used to end the exposure and sample the information indicative of a time passed since a beginning of exposure when the integration output is equal to the reference signal. Thus, both the integration output and the information indicative of a time passed since a beginning of exposure are known at time of sampling and the gradient is determined.

[0101] In some embodiments the circuitry further comprises plurality of photodiodes, a plurality of gain amplifiers, wherein a signal of each photodiode of the plurality of photodiodes is amplified by a corresponding gain amplifier of the plurality of gain amplifiers, and wherein the circuitry is configured to dynamically change the output of each gain amplifier of the plurality of amplifiers during exposure in response to a feedback signal.

[0102] The plurality of photodiodes may be multiple individual photodiodes that are present in the image device. Each photodiode is responsible for capturing light and converting it into an electrical signal.

[0103] The plurality of amplifiers may be multiple individual amplifiers that each are associated with a corresponding photodiode in the image device. Each amplifier is responsible for amplifying the electrical signal generated by the corresponding photodiode. By having a separate amplifier for each photodiode, the circuitry can dynamically adjust the gain of each amplifier independently during exposure, allowing for more precise control over the signal amplification, in particular in high dynamic ranges.

[0104] The circuitry may be configured to dynamically change the output of each gain amplifier of the plurality of amplifiers during exposure. Thus, the circuitry may be what is refereed to as global circuitry for an entire 2D array of photodiodes and corresponding amplifiers. However, the circuitry may also dynamically change the output of each gain amplifier of the plurality of amplifiers during exposure, wherein both the plurality of photodiodes and the plurality of amplifiers corresponds to a row, a column, or an area of a 2D array of photodiodes. The controller status (information indicative of time passed since the beginning of exposure) maybe used to determine the level of illumination received, providing information about the intensity of the light. This information is then used to map the exposure time or the gradient signal, which is indicative of the light intensity, using a lookup table. This mapping can be done on a per pixel, row, column, area, or global basis.

[0105] The predetermined reference signal, which can be a reference threshold or the saturation of the controller, is used to determine when the frame acquisition process ends. This occurs either when the reference threshold is reached or when the controller (counter) becomes saturated.

[0106] During the frame acquisition process, the device can dynamically change the amplification of the signal received from the photodiode by changing the output signal of the amplifier. This allows for a high dynamic range and shorter acquisition time. The controller can also be a PID controller or a digital-to-digital Delta-Sigma modulator.

[0107] Depending on the implementation of the controller, there is a trade-off between complexity and performance. The PID method is a more sophisticated algorithm, but a simpler version can use a counter to control the modulation of a PWM, followed by an integrator as described above.

[0108] The controller can be fully analog up to the A / D converter, or partially digital with a counter, eliminating the need for an explicit A / D converter. In the latter case, a separate D / A converter is required. In certain digital embodiments, such as using a counter as the controller, the circuit can be simplified by replacing the counter and D / A converter with a digital-to-digital Delta-Sigma modulator and low-pass filter.

[0109] The output of the controller is inversely proportional to the illumination, but the specific relationship depends on the type of controller used. Additionally, it is proposed to store the gradient instead of the intensity value per pixel, which could potentially become a new standard for image acquisition and storage.

[0110] In some embodiments a method for controlling a gain controlled solid-state imaging device, comprises amplifying, by a gain amplifier, the output of a photodiode, and dynamically changing the output of the gain amplifier during exposure in response to a feedback signal.

[0111] In some embodiments a computer program comprises instructions which, when the program is executed by a computer, cause the computer to carry out the method above.

[0112] The methods as described herein may also be implemented in some embodiments as a computer program causing a computer and / or a processor to perform the method, when being carried out on the computer and / or processor. In some embodiments, also a non-transitory computer- readable recording medium is provided that stores therein a computer program product, which, when executed by a processor, such as the processor described above, causes the methods described herein to be performed.

[0113] Fig. 1 is a schematic diagram of an imaging device, specifically designed for an image sensing application, such as a camera.

[0114] The imaging device 100 is an analog circuit and performs a voltage measurement for a set exposure time.

[0115] The imaging device 100 comprises a photodiode 101, an amplifier 102, a gain 103, an integrator 104, a reset 105, an exposure time 105, a sequencer 107, a sampler 108, and an analog-to-digital converter 109. The arrows connecting the individual units of the imaging device 100 (and also the units of the imaging devices of following Figures) are dashed if they pertain to control signals, values that are set before exposure begins or provide signals of oscillators or integration constants. Arrows with a solid line are a voltage signal of the photodiode 101 or indicative (explicitly or implicitly over feedback) of the voltage signal of the photodiode 101.

[0116] Photodiode 101 is a photosensitive area that converts incident light into an electrical signal to obtain a voltage signal indicative of the amount of converted incident light. In camera systems, photodiodes are used to capture light that is reflected from an object.

[0117] Amplifier 102 amplifies the voltage signal coming from photodiode 101, thus increasing the strength of the voltage signal to obtain an amplified voltage signal for further processing.

[0118] Gain 103 is an amplification factor of the amplifier 102 determining a relative amount of increase in strength of the voltage signal coming from photodiode 101 to the amplified voltage signal. Gain 103 is used to adjust the sensitivity of the imaging device 100, e.g. in different lighting conditions.

[0119] Integrator 104 accumulates the amplified voltage signal over an exposure time to obtain an accumulated voltage signal. This is useful for getting a stronger signal in low light conditions.

[0120] Exposure time 106 is a control signal that controls how long the light is allowed to be converted in the photodiode and how long the resulting amplified voltage signal is accumulated in integrator 104.

[0121] Sequencer 107 controls the timing sequence of integrator 104 and sample 107, such that the amplified voltage signal is accumulated in the amplifier for exposure time 106 and sample the accumulated voltage signal at the end of exposure time 106. Sequencer 107 controls the timing sequence of integrator 104 with a reset 105 of the accumulation of the amplified voltage signal at the beginning of exposure time 106.

[0122] Sample 108 is a sampling function that captures the accumulated voltage signal at a specific moment determined by sequencer 107 at the end of exposure time 106 to obtain a sampled voltage signal for further processing.

[0123] Analog-to-Digital Converter (ADC) 109 converts the sampled voltage signal, which is an analog signal, into a digital signal that can be handled by a computer or digital processing unit.

[0124] Fig. 2 is a diagram showing an example of an implementation of the imaging device of Fig. 1.

[0125] Components or groups of components with the same reference signs as depicted in Fig. 1 and described with reference to Fig. 1 are the same components in Fig. 2.

[0126] The photodiode 101 is connected to ground on one connection, and a voltage signal that is proportional to the light received by the photodiode 101 is output on the other connection of the photodiode 101. The voltage signal of the photodiode is input to an input terminal of the amplifier 102.

[0127] The amplifier 101 consists of an amplification circuit and a gain 103, configured as a resistor, in a parallel arrangement with the amplification circuit. The resistor is connected to one input terminal and one output terminal of the amplification circuit. The resistor may be variable and used to set the amplification gain 103 for the amplifier 102. The voltage signal is received by the input terminal of the amplification circuit that is also connected to the resistor. Thus, the voltage signal is also received by the resistor. Another input terminal of the amplification circuit is connected to ground. An output terminal of the amplifier 102 is connected via another resistor to an input terminal of the integrator 104 and outputs an amplified voltage signal amplified in accordance with the gain 103 to the input terminal of the integrator 104.

[0128] The integrator 104 consists of an amplification circuit a capacitor and a switch in a parallel arrangement. The capacitor and the switch are each connected to one input terminal and one output terminal of the amplification circuit. The amplified voltage signal is received by the input terminal of the amplification circuit that is also connected to the capacitor and the switch. Thus, the amplified voltage signal is also received by the capacitor and the switch. Another input terminal of the amplification circuit is connected to ground. An output terminal of the integrator 102 is connected to the sample 108 which is implemented as a switch. The integrator 104 outputs an accumulated voltage signal to the input of the sample 108. The switch of the integrator 104 can be used to reset 105 the integrator 104.

[0129] The sequencer 107 receives the exposure time 106 and controls the switch of the integrator 104 and provides a signal indicating the ADC 109 to sample to accumulate the amplified voltage signal for intended the exposure time 106. Consequently, the sequencer 107 resets the integrator 104 via the reset 105 at the beginning of the exposure time 106 and samples the accumulated voltage signal of the integrator 104 with the sample 108 at the end of the exposure time 106 to obtain a sampled voltage signal. The sequencer 107 may be a timer.

[0130] The ADC 109 converts the sampled voltage signal, which is an analog signal, into a digital signal. The ADC 109 further implements the sample (circuit) 108 which may comprise a switch that switches in reaction to the signal indicating the ADC 109 to sample.

[0131] The controllable inputs if the imaging device of Fig. 1 and 2 are the exposure time 106 and the gain 103.

[0132] Fig. 3 is a flowchart of the operation of an imaging device of Fig. 1 and Fig. 2.

[0133] The operation method 150 begins at 151 with setting a gain (103 in Fig. 1 and 2) in the amplifier (102 in Fig. 1 and 2) and setting an exposure time (106 in Fig. 1 and 2) in the sequencer (107 in Fig. 1 and 2).

[0134] At 152, the amplified voltage signal (output of amplifier (102 in Fig. 1 and 2)) is integrated over the exposure time to obtain the accumulated voltage signal (integration output of integrator (104 in Fig. 1 and 2)). The sequencer (107 in Fig. 1 and 2) resets the integrator 104 via the reset 105 at the beginning of the exposure time (106 in Fig. 1 and 2).

[0135] At 153, the accumulated voltage signal is sampled as the integration output. The sequencer (107 in Fig. 1 and 2) samples the accumulated voltage signal of the integrator (104 in Fig. 1 and 2) with the sample 108 at the end of the exposure time 106 to obtain a sampled voltage signal.

[0136] Fig. 4 is a schematic diagram of an imaging device, specifically designed for an image sensing application, such as a camera.

[0137] The imaging device 200 is an analog circuit and performs a time measurement from as start of a set exposure time until a reference value for an accumulated voltage signal indicative of a light received by a photodiode is reached. The imaging device 200 comprises a photodiode 201, an amplifier 202, a gain 203, an integrator 204, a comparator 212, a reference 211, a sequencer 207, a reset 205, an integrator 213, a constant 214, a sample 208, and an ADC 209.

[0138] Where the photodiode 201, the amplifier 202, the gain 203, the integrator 204, the sequencer 207 the reset 205, the sample 208, and the ADC 209 are respectively the same as the photodiode 101, the amplifier 102, the gain 103, the integrator 104, the sequencer 107 the reset 105, the sample 108, and the ADC 109 of Fig. 1 and Fig. 2 a description will be omitted.

[0139] The comparator 212 receives an accumulated voltage signal of the integrator 214 and compares the accumulated voltage signal with a reference signal. The reference 211 provides the fixed reference signal to the comparator 212. The output of the comparator 212 is a comparator control signal based on the result of the comparison. The comparator control signal is output to the sample 208 and is used to control the sample 208.

[0140] The constant 214 provides a set integration constant to the integrator 213. The integrator 213 receives the integration constant from constant 214 and integrates the integration constant to obtain a measure of time (e.g. information indicative of a time passed from a beginning of an exposure) since the integrator 213 is reset by the sequencer 207 and transmits the measure of time to the sample 208.

[0141] The sequencer 207 controls the reset 205 to reset the integrators 204 and 213. The reset of the integrator 204 is the same as resetting the integrator (104 in Fig. 1 and 2) by the sequencer (107 in Fig. 1 and 2). However, the sequencer 207 does not control the sample 208 and receives no exposure time. Thus, sequencer 207 starts the exposure but does not end it.

[0142] The sequencer 207 controls the switch of the integrator 213 to accumulate the integration constant. Consequently, the sequencer 207 resets the integrator 213 via the reset 205 at the beginning of the exposure. The reset 205 is controlled by the sequencer 207 and resets the integrators 204 and 213.

[0143] When the comparator 212 determines that the accumulated voltage signal has reached the reference signal, the comparator controls the sample 208 to sample the measure of time received by the sample 208 from the integrator 213. Then the ADC 209 converts the measure of time, which is an analog signal, into a digital signal.

[0144] Consequently, the imaging device 200 integrates both a voltage signal indicative of the received light and an integration constant until the integration of the signal indicative of the received light has reached a reference signal and then samples the time derived as the integrated integration constant. The exposure time is theoretically open-ended.

[0145] Fig. 5 is a diagram showing an example of an implementation of the imaging device of Fig. 4.

[0146] Components or groups of components with the same reference signs as depicted in Fig. 4 and described with reference to Fig. 4 are the same components in Fig. 5.

[0147] The comparator 212 receives the accumulated voltage signal of the integrator 204 at one of its input terminals and the reference signal at the other input terminal.

[0148] The constant 214 and the reference 211 are circuits that provide constant voltage levels as the integration constant and the reference signal. The circuits comprise in series a voltage source, a resistor, a diode, and a ground. The constant voltage is provided from a node between the resistor and the diode, while the diode can be used to determine a specific constant voltage level.

[0149] The integrator 213 receives the integration constant from constant 214 and accumulates it to obtain a measure of time, which is a voltage signal. The integrator 213 has the same layout as the integrator 204. Both layouts are described as integrator 104 with reference to Fig. 2.

[0150] The sequencer 207 controls the switches of the integrators 204 and 213 and resets the integrators 204 and 213 simultaneously to start the exposure. The exposure is ended by the comparator 212 when the accumulated voltage signal has reached the reference signal. Then, the comparator controls the sample (circuit) 208, which is implemented in the ADC 209, to sample the measure of time and transmit the sampled measure of time in the ADC 209, which converts the measure of time into a digital signal. The comparator 212 thus provides a signal indicating the ADC 209 to sample. The sample (circuit) 108 may comprise a switch that switches in reaction to the signal indicating the ADC 109 to sample. In case of a saturation, the sampled measure of time may correspond to a black pixel. The picture may be inverse. If the measure of time is too long i.e. a large number. The inverse of the measure of time is small. If the number is large enough, the inverse may be approximated with zero which may correspond to black.

[0151] The controllable inputs of the imaging device of Fig. 4 and 5 are the gain, the reference signal and the integration constant.

[0152] Fig. 6 is a flowchart of the operation of an imaging device of Fig. 4 and Fig. 5.

[0153] The operation method 250 begins at 251 with setting a gain (203 in Fig. 4 and 5) in the amplifier (202 in Fig. 4 and 5), setting a reference signal (211 in Fig. 4 and 5) for the comparator (212 in Fig. 4 and 5) and setting an integration constant (214 in Fig. 4 and 5) for the integrator (213 in Fig. 4 and 5).

[0154] At 252, the integration constant is integrated to obtain a measure of time and the amplified voltage signal (output of the amplifier 202 in Fig. 4 and 5) is integrated to obtain the accumulated voltage signal.

[0155] At 253, it is checked whether the accumulated voltage signal has reached the reference signal.

[0156] At 254, if the accumulated voltage signal has reached the reference signal, the measure of time is sampled as the pixel value corresponding to the light received by the photodiode.

[0157] Fig. 7 is a schematic diagram of an imaging device, specifically designed for an image sensing application, such as a camera.

[0158] The imaging device 300 is a partially digital circuit and performs a time measurement from as start of a set exposure time until a reference value for an accumulated voltage signal indicative of a light received by a photodiode is reached.

[0159] The imaging device 300 comprises a photodiode 301, an amplifier 302, a gain 303, an integrator 304, a comparator 312, a reference 311, a sequencer 307, a reset 305, a counter 313, an oscillator 314, a sample 308, and a buffer 309.

[0160] The difference to Fig. 4 is, that the integrator 213, constant 214 and ADC 209 are respectively replaced by digital circuits, namely the counter 313, the oscillator 314 and the buffer 309. The remaining components are the same and description thereof will be omitted.

[0161] The oscillator 314 oscillates with a set frequency and outputs the oscillating signal to the counter 313. The counter counts the oscillations to obtain a measure of time, which in this case is a digital measure of time. The sequencer 307 resets the counter 313 and the integrator 304 via the reset 305 and starts the exposure by resetting the counter 313 and the integrator 304 simultaneously. The sequencer 307 receives no exposure time. Thus, the sequencer 307 does not end exposure.

[0162] In the same way as described for the imaging device (200 with reference to Fig. 4 and 5) the comparator 312 determines that the accumulated voltage signal has reached the reference signal controls the sample 308 to sample the measure of time received by the sample 308 from the counter 313. In case of saturation, the measure of time corresponds to a black pixel.

[0163] The sampled measure of time, which is a digital signal, is then transmitted via the sample 308 and stored in the buffer 309. Fig. 8 is a diagram showing an example of an implementation of the imaging device of Fig. 7.

[0164] Components or groups of components with the same reference signs as depicted in Fig. 7 and described with reference to Fig. 7 are the same components in Fig. 8.

[0165] The difference to Fig. 5 is, that the integrator 213, constant 214 and ADC 209 are respectively replaced by digital circuits, namely the counter 313, the oscillator 314 and the buffer 309. The remaining components are the same and description thereof will be omitted.

[0166] The counter 313 is an exemplary 4-bit counter which is implemented by four flip-flop circuits and adders. The counter 313 can, however, be any circuit layout of a counter. The oscillator 314 outputs an oscillation signal to the clock terminal of each flip-flop circuit. The flip-flop circuits count the numbers of oscillations, wherein each flip-flop circuit determines the output of one bit in the binary representation such that the counter 313 outputs a binary signal representing the counted oscillations.

[0167] The sequencer 307 can start and reset the count in the counter 313 via the input marked “Logic 1”.

[0168] When the comparator 312 determines that the accumulated voltage signal has reached the reference signal the comparator controls the sample (circuit) 308 to sample the measure of time received by the sample 308 from the counter 313. The sampled measure of time, which is a digital signal is then transmitted via the sample 308 and stored in the buffer 309. Thus, the sample 308 writes the measure of time to the buffer 309.

[0169] The controllable parameters are the gain, the reference signal and the oscillation frequency.

[0170] Fig. 9 is a flowchart of the operation of an imaging device of Fig. 7 and Fig. 8.

[0171] The operation method 350 begins at 351 with setting a gain (303 in Fig. 7 and 8) in the amplifier (302 in Fig. 7 and 8), setting a reference signal (311 in Fig. 7 and 8) for the comparator (312 in Fig. 7 and 8) and setting an oscillation frequency in the oscillator (314 in Fig. 7 and 8) for the counter (313 in Fig. 7 and 8).

[0172] At 252, the oscillations of the oscillator are counted to obtain a measure of time and the amplified voltage signal (output of the amplifier 302 in Fig. 7 and 8) is integrated to obtain the accumulated voltage signal.

[0173] At 253, it is checked whether the accumulated voltage signal has reached the reference signal.

[0174] At 254, if the accumulated voltage signal has reached the reference signal the measure of time is sampled as the pixel value corresponding to the light received by the photodiode. Fig. 10 is a schematic diagram of a gain-controlled imaging device according to an embodiment of the present disclosure, specifically designed for an image sensing application, such as a camera.

[0175] The gain-controlled imaging device 400 is an analog circuit and performs a gain-controlled time measurement from as start of a set exposure time until a reference value for an accumulated voltage signal indicative of a light received by a photodiode is reached.

[0176] The imaging device 100 comprises a photodiode 401, an amplifier 402, an integrator 404, a reset 405, a sequencer 407, a sample 408, an analog-to-digital converter 409, a reference 411, a difference 412 and a controller 413.

[0177] The difference to Fig. 1 is, the addition of a difference 412 with reference 411, the controller 413, and feedback (a feedback loop) from the controller 413 to the amplifier 402, which replaces the fixed gain (103 in Fig. 1 and 2).

[0178] The difference 412 receives the accumulated voltage signal from the integrator 404 and a reference signal from the reference 411. The difference 412 then determines a difference signal based on the accumulated voltage signal and the reference signal and outputs the difference signal to the controller 413.

[0179] The controller 413 receives the difference signal and determines an input gain and an output signal indicative of the light received by the photodiode 401. The controller 413 then outputs the input gain to the amplifier 402 and thus controls the amplifier 402 and dynamically changes the input gain, in particular the controller 413 dynamically controls the amplification factor of the amplifier 402. Further, the controller 413 outputs the signal indicative of the light received by the photodiode 401 to the sample 408. The controller 413 may be an integrator with a predetermined gain.

[0180] For example, the difference 412 is a comparator, that compares the accumulated voltage signal and the reference signal to obtain a comparison signal that is a high voltage level when the accumulated voltage signal has not reached the reference signal and a low voltage level when the accumulated voltage signal has reached the reference signal. The comparator outputs the comparison signal to the controller 413. Further, the comparator determines a comparison error and outputs the comparison error to the sample 408.

[0181] In that example, the controller 413 may be an integrator that integrates the comparison result, like an integration constant, to obtain a measurement of time as the signal indicative of the light received by the photodiode 401. Further, the measure of time may be used to dynamically change the input gain of the amplifier 402. This dynamic change may be performed via a predetermined function, a look-up table or measure of time, that is an analog voltage signal, is feed directly to a resistor in the amplifier 402 which is an example implementation described in detail with reference to Fig. 11. The measure of time may further be output to the sample 408.

[0182] Further, when the comparison error reaches zero the comparison signal changes to the low voltage level and the sample 408 samples the measure of time of the controller 413 and transmits the measure of time to the ADC 409.

[0183] The ADC 409 converts the measure of time into a digital signal.

[0184] In this way, the gain of the amplifier can be dynamically changed within the time of exposure a convergence of the accumulated voltage signal to the reference signal can be achieved. For example, the gain can be increased as the measure of time increases (for example proportionally) so that the amplification factor increases and a convergence of the accumulated voltage signal to the reference signal is increases as the measure of time increases.

[0185] Since the predetermined function, the look-up table or the proportionality of the gain with the measure of time is known, the intensity can be determined based in the measure of time while the exposure time of a time measurement is decreased.

[0186] Fig. 11 is a diagram showing an example of an implementation of the imaging device of Fig. 10.

[0187] Components or groups of components with the same reference signs as depicted in Fig. 10 and described with reference to Fig. 10 are the same components in Fig. 11.

[0188] The circuit layout is based on the one of Fig. 2 with the addition of a difference 412 formed as a comparator, a reference 411, the controller 413 formed as an integrator, and feedback (a feedback loop) from the output of the controller 413 to the resistor of the amplifier 402, which replaces the fixed gain (103 in Fig. 1 and 2) of the amplifier 402.

[0189] As describe above, the difference 412 is a comparator, that compares the accumulated voltage signal and the reference signal to obtain a comparison signal that is a high voltage level when the accumulated voltage signal has not reached the reference signal and a low voltage level when the accumulated voltage signal has reached the reference signal. The accumulated voltage signal is provided from the integrator 404 and the reference signal is provided by the reference 411 that is configured like the references (211 and 214) in Fig. 5. The comparator outputs the comparison signal to the controller 413. Further, the comparator determines a comparison error and outputs the comparison error to the sample 408. Here, the sample (circuit) 408, which is implemented in the ADC 409, is connected to a further comparator 414 and a further reference 415 providing a further reference signal. The further reference signal may be a signal of low voltage or zero voltage of a signal of close to zero voltage. The further comparator 414 receives the comparison error at one input terminal and the further reference signal at the other terminal of the comparator 414. When the comparison error reaches the further reference signal (or crosses the further reference signal, e.g. due to a hysteresis in the comparator) the comparator controls the sample (circuit) 408 in the ADC 409, with a signal indicating the ADC 409 to sample, to sample the output of the controller 413. The comparison signal also changes to the low voltage level. The sample (circuit) 408 which may comprise a switch that switches in reaction to the signal indicating the ADC 409 to sample.

[0190] The controller 413 is implemented as an integrator, just like the integrator 404 (describe as integrator 104 with reference to Fig. 2) that accumulates the comparison result, like an integration constant, to obtain a measurement of time as the signal indicative of the light received by the photodiode 401. Further, the measure of time is used to dynamically change the input gain of the amplifier 402. This dynamic change is performed via a direct feedback of the measure of time, that is an analog voltage signal, to the resistor in the amplifier 402. The measure of time is further the output that is sampled by the sample 408. The integrator in the controller 413 is also reset via a switch controlled by the sequencer at the beginning of the exposure time.

[0191] The controllable inputs of the imaging device of Fig. 10 and 11 are the reference signal and the integration gain.

[0192] Fig. 12 is a flowchart of the operation of an imaging device of Fig. 10 and Fig. 11.

[0193] The operation method 450 begins at 451 with setting a preliminary gain in the amplifier (402 in Fig. 10 and Fig. 11) and setting a reference signal for the difference (comparator) 412.

[0194] At 452, the amplified voltage signal (an output of the amplifier 402 in Fig. 10 and 11) is integrated to obtain an accumulated voltage signal.

[0195] At 453, a comparison signal and an error of the accumulated voltage signal to the reference signal is computed (by the difference 412 in Fig. 10 and 11) and the comparison signal (high / low voltage signal) is integrated (by controller 413 in fig. 10 and 11) to obtain a measure of time as an integration output.

[0196] At 454, the integration of the comparison signal is continued to obtain the integration output. The integration is performed with feedback to the gain, computed by the controller based on the computed comparison signal. The feedback may be the integration output, which because of the high / low comparison signal may be the result of an integration of a constant. This integration output is thus both a measure of time and also an analog voltage signal, that can be used to control the resistor in the amplifier (402 in Fig. 10 and 11), which controls the gain in the amplifier (402 in Fig. 10 and 11).

[0197] At 455, it is checked whether the computed error approaches zero, or whether the computed error is zero, or a predetermined value close to zero.

[0198] At 456 if the computed error approaches zero (or the alternative checks of 455 are fulfilled) the integration output is sampled.

[0199] Fig. 13 is a schematic diagram of a gain-controlled imaging device according to an embodiment of the present disclosure, specifically designed for an image sensing application, such as a camera.

[0200] The imaging device 500a is a partially digital circuit and performs a gain-controlled time measurement from as start of a set exposure time until a reference value for an accumulated voltage signal indicative of a light received by a photodiode is reached.

[0201] The imaging device 500a comprises a photodiode 501, an amplifier 502, a digital-to-analog- converter (DAC) 510a, an integrator 504, a comparator 512, a reference 511, a sequencer 507, a reset 505, a controller 513, an oscillator 514, a sample 508, and a buffer 509.

[0202] The difference to Fig. 7 is the addition of a DAC 510a with reference 516 which replace the gain (303 in Fig. 7) and the controller 513 which may be a counter as depicted in Fig. 7 but also may be any other controlling device.

[0203] The sequencer 507 provides a start signals to the controller 513 simultaneously to the reset 505 being controlled by the sequencer 507 to reset the integrator 504.

[0204] The oscillator 514 generates an oscillating signal and provides the oscillating signal to the controller.

[0205] The controller 513 receives the oscillating signals and the start signal and from the start signal determines a measure of time based on the oscillating signal, wherein the measure of time is a digital signal. The measure of time may be determined by counting the oscillations. The controller then provides the measure of time to the DAC 510a and the sample 508. The controller 513 could be a counter. In that case, the combination of a counter and the DAC 510a can be realized with a Delta Sigma scheme and an analog low-pass filter. The DAC 510a receives the amplified voltage signal from the amplifier 502 and the measure of time from the controller 513. The measure of time is a digital input. The amplified voltage signal is input into the reference voltage input of the DAC 510a. As describe pertaining to the DAC above, based on the ratio of the digital input, that is the measure of time to a maximum digital value (e.g. 255 in an 8-bit system) the amplified voltage signal is attenuated to obtain an attenuated amplified voltage signal that is transmitted to the integrator 504 and integrated there.

[0206] With the changing of the voltage of the amplified voltage signal passing through the DAC 510a the gain of the amplifier 502 can be attenuated, thus amplifier 502 and DAC 510a are controlled by the controller to dynamically change the gain of the amplified voltage signal. Further, for purposes of describing gain feedback, the DAC 510a is depicted as a component separate from the amplifier 502. However, the DAC may be comprised in the amplifier 502.

[0207] Further, some gain should be predefined in the DAC 510a, which is updated with the feedback of the measure of time.

[0208] The operation of integrator 504, comparator 512, reference 511 and sample 508 in Fig. 13 is the same as the operation of integrator 304, comparator 312, reference 311 and sample 308 in Fig. 7, with the difference that the analog amplified voltage signal is input into the integrated instead of the amplified voltage signal and the measure of time is sampled from the controller 513 instead of the counter (313 in Fig. 7).

[0209] Fig. 14 is a diagram showing an example of an implementation of the imaging device of Fig. 13.

[0210] Components or groups of components with the same reference signs as depicted in Fig. 13 and described about Fig. 13 are the same components in Fig. 14.

[0211] The difference to Fig. 8 is the DAC 510a placed in between the amplifier 502 and the integrator 504.

[0212] The controller 513 is implemented as a counter for the purposes of Fig. 14. The measure of time, which is the output of the controller 513 is provided to the sample 508 and the DAC 510a.

[0213] Consequently, based on the measure of time output by the counter implementing the controller 513 the DAC attenuates the amplified voltage signal from the amplifier 502 to obtain the analog amplified voltage signal and provides the analog amplified voltage signal to the integrator 504. Thus, the gain of the combination of the amplifier 502 and the DAC 510a is dynamically changed based on the measure of time output by the controller. The controllable inputs of the imaging device of Fig. 13 and 14 are the reference signal and the oscillation frequency.

[0214] Fig. 15 is a schematic diagram of a gain-controlled imaging device according to an embodiment of the present disclosure, specifically designed for an image sensing application, such as a camera.

[0215] The imaging device 500b is a partially digital circuit and performs a time measurement from as start of a set exposure time until a reference value for an accumulated voltage signal indicative of a light received by a photodiode is reached.

[0216] The imaging device 500b comprises a photodiode 501, an amplifier 502, a pulse with modulator (PWM) 510b, an integrator 504, a comparator 512, a reference 511 , a sequencer 507, a reset 505, a counter 513, an oscillator 514, a sample 508, and a buffer 509.

[0217] The difference to Fig. 13 is the replacement of the DAC 510a with the PWM 510b and that the controller as depicted in Fig. 13 is implemented as the counter 513. Further the reset 505 may or may not be provided, it is however not depicted in Fig. 15.

[0218] As already described with reference to Fig. 13 the counter 513 implementing the controller determines a measure of time based on a start signal from the sequencer 507 and the oscillation signal from the oscillator 514. Because of the PWM the integrator 504 does not need to be reset.

[0219] The PWM 510b receives the amplified voltage signal from the amplifier 502and a signal based on the measure of time from the counter 513. The signal based on the measure of time may be digital signals. Based on the amplified voltage signal and signal based on the measure of time, a pulse width modulated signal is obtained. The pulse width modulated signal is a voltage signal alternating between a high voltage level and a low voltage level repeated in a duty cycle. The high voltage level may be the voltage level of the amplified voltage signal or a voltage level indicative thereof and the low voltage level may be zero volts. The signal based on the measure of time may control the length of the high voltage level in a duty cycle. Therefore the measure of time may be used to dynamically change the duty cycle of the PWM 510b and thus switch the amplified voltage signal on and off in accordance with the duty cycle. This leads to an attenuation of the amplification of the combination of amplifier 502 and PWM 510b, which is then integrated in the integrator 504.

[0220] The integrator 504 is an analog integrator that receives the pulse width modulated signal as an integration constant that is switched from a high voltage level where the voltage may be integrated to a low voltage level that may be zero, such that no additional integration (accumulation) occurs. Thus, the integration constant is switch on and off in relation to the measure of time determined and output by the counter 513, which changes the overall gain of the amplifier 502 and the PWM 510b.

[0221] Amplifier 502 and PWM 510b are depicted as two separate components but be PWM may also be comprised in the amplifier 502.

[0222] Consequently, the counter 513 dynamically changes the gain of the combination of amplifier 502 and PWM 510b.

[0223] The controllable inputs of the imaging device of Fig. 15 and 16 are the reference signal and the oscillation frequency.

[0224] Fig. 16 is a diagram showing an example of an implementation of the imaging device of Fig. 15.

[0225] Components or groups of components with the same reference signs as depicted in Fig. 15 and described with reference to Fig. 15 are the same components in Fig. 16.

[0226] The difference to Fig. 14 is the PWM 510b placed in between the amplifier 502 and the integrator 504.

[0227] The counter 513 determines and outputs a measure of time. The measure of time is provided to the sample 508 and the DAC 510a.

[0228] Consequently, based on the measure of time output by the counter 513 the PWM obtains a pulse width modulated signal based on the amplified voltage signal from the amplifier 502 and provides the pulse width modulated signal to the integrator 504. The integrator 504 integrates the pulse width modulated signal, which is an integration constant that is switched on and off. Thus, the gain of the combination of the amplifier 502 and the PWM 510b is dynamically changed based on the measure of time output by the controller.

[0229] Fig. 17 is a flowchart of the operation of an imaging device of Fig. 13 to Fig. 16.

[0230] The operation method 550 begins at 551 with setting a comparison reference for the comparator (512 in Fig. 13 to Fig. 16) and setting an oscillation frequency in the oscillator (514 in Fig. 13 to Fig. 16).

[0231] At 552, the amplified voltage signal (an output of the amplifier 502 in Fig. 13 to Fig. 16) is integrated to obtain an accumulated voltage signal, the oscillations of the oscillator are counted to obtain a measure of time (an integration time) and feedback a gain (a feedback loop of a gain) to the amplifier (502 in fig. 13 to 16) based on the measure of time is performed. At 553, it is checked whether the accumulated voltage signal has reached the comparison reference.

[0232] At 554, If the accumulated voltage signal has reached the comparison reference, sample the integration time.

[0233] Fig. 18a is a graph comparing a pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16.

[0234] Depicted is a graph showing a pixel response on the y-axis in relative units from 0 to 0.5 over the relative light from 0 to 10, which is the light received by the photodiode of the respective imaging devices.

[0235] Further depicted are the pixel response of a time measurement 580 without gain control and the pixel response of a gain-controlled time measurement 581 performed by a gain-controlled imaging device according to an embodiment.

[0236] The pixel response of the time measurement 580 drops from approximately 0.025 to 0 between a relative light from approximately 0 to 0.2. The drop is asymptotic.

[0237] The pixel response of the gain-controlled time measurement 581 drops from approximately 0.15 to 0.01 between a relative light from approximately 0 to 10. The drop is also asymptotic.

[0238] Consequently, the pixel response in the gain-controlled time measurement 581 is higher across the depicted range of relative light from 0 to 10. Furthermore, the pixel response of the gain- controlled time measurement 581 still is a useful signal at a higher relative lights, particularly over a relative light of approximately 0.2. Therefore, the dynamic range of the gain-controlled time measurement 581 performed by a gain-controlled imaging device according to an embodiment is higher.

[0239] Fig. 18b is a graph comparing an inverse pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16.

[0240] Depicted is a graph showing an inverse pixel response on the y-axis in relative units from 0 to 1000 over the relative light from 0 to 10, which is the light received by the photodiode of the respective imaging devices. The inverse pixel response of the time measurement 580 increases in steps, which may be caused by digitization, from approximately 0 to 1000 between a relative light from approximately 0 to 1. Thereafter, the inverse pixel response of the time measurement 580 is outside the depicted range of the inverse pixel response.

[0241] The inverse pixel response of the gain-controlled time measurement 581 increases in smaller steps than the steps of the inverse pixel response of the time measurement 580, which may also be caused by digitization, from approximately 0 to 100 between a relative light from approximately 0 to 10. The increase is approximately logarithmic.

[0242] Consequently, the inverse pixel response in the gain-controlled time measurement 581 is lower across the depicted range of relative light from 0 to 10. Furthermore, the inverse pixel response of the gain-controlled time measurement 581 still is a useful signal at a higher relative light, particularly over a relative light of approximately 1 as the inverse pixel response of the time measurement 580 is outside the depicted range of the inverse pixel response. Therefore, the dynamic range of the gain-controlled time measurement 581 performed by a gain-controlled imaging device according to an embodiment is higher.

[0243] Fig. 18c is a graph comparing an inverse normalized pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16.

[0244] Depicted is a graph showing an inverse normalized pixel response on the y-axis in relative units from 0 to 1 over the relative light from 0 to 10, which is the light received by the photodiode of the respective imaging devices.

[0245] The inverse normalized pixel response of the time measurement 580 increases in steps, which may be caused by digitization, from approximately 0 to 1 between a relative light from approximately 0 to 1. Thereafter, the inverse normalized pixel response of the time measurement 580 is outside the depicted range of the inverse normalized pixel response.

[0246] The inverse normalized pixel response of the gain-controlled time measurement 581 increases from approximately 0 to 1 between a relative light from approximately 0 to 10. The increase is approximately logarithmic.

[0247] There are two graphs of inverse normalized pixel response of the gain-controlled time measurement 581. One increases in a smooth graph and is obtained with the analog gain- controlled imaging device of Fig. 10 and 11, the other increases in smaller steps than the steps of the inverse normalized pixel response of the time measurement 580, which may also be caused by digitization, and is obtained with the gain-controlled imaging device of Fig. 13 to 16.

[0248] Consequently, the inverse normalized pixel response in the gain-controlled time measurement 581 is lower across the depicted range of relative light from 0 to 10. Furthermore, the inverse normalized pixel response of the gain-controlled time measurement 581 still is a useful signal at a higher relative light, particularly over a relative light of approximately 1 as the inverse normalized pixel response of the time measurement 580 is outside the depicted range of the inverse normalized pixel response. Therefore, the dynamic range of the gain-controlled time measurement 581 performed by a gain-controlled imaging device according to an embodiment is higher.

[0249] As the relative light increases all the graphs of Fig. 18a to 18c depict gain-controlled measurement with a flatter response. There exists a sweet spot where a good dynamic is present. Further, the overall dynamic range is very high.

[0250] Fig. 19a is a graph comparing a pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16.

[0251] Depicted is a graph showing a pixel response on the y-axis in relative units from 0 to 0.5 over the relative light from 0 to 1, which is the light received by the photodiode of the respective imaging devices.

[0252] Further depicted are the pixel response of a time measurement 580 without gain control and the pixel response of a gain-controlled time measurement 581 performed by a gain-controlled imaging device according to an embodiment.

[0253] The pixel response of the time measurement 580 and gain-controlled time measurement 581 can be separated from the y-axis and x-axis for higher pixel responses and at higher relative lights because the range of relative light is smaller than depicted in Fig. 18a.

[0254] The pixel response of the time measurement 580 drops from approximately 0.2 to 0 between a relative light from approximately 0 to 0.3. The drop is asymptotic.

[0255] The pixel response of the gain-controlled time measurement 581 drops from approximately 0.45 to 0.035 between a relative light from approximately 0 to 1. The drop is also asymptotic.

[0256] Consequently, the pixel response in the gain-controlled time measurement 581 is higher across the depicted range of relative light from 0 to 1. Furthermore, the pixel response of the gain- controlled time measurement 581 still is a useful signal at a higher relative lights, particularly over a relative light of approximately 0.3. Therefore, the dynamic range of the gain-controlled time measurement 581 performed by a gain-controlled imaging device according to an embodiment is higher.

[0257] Fig. 19b is graph comparing an inverse pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16.

[0258] Depicted is a graph showing an inverse pixel response on the y-axis in relative units from 0 to 500 over the relative light from 0 to 1, which is the light received by the photodiode of the respective imaging devices.

[0259] The inverse pixel response of the time measurement 580 increases in steps, which may be caused by digitization, from approximately 0 to 500 between a relative light from approximately 0 to 0.5. Thereafter, the inverse pixel response of the time measurement 580 exits the depicted range of inverse pixel response.

[0260] The inverse pixel response of the gain-controlled time measurement 581 increases in smaller steps than the steps of the inverse pixel response of the time measurement 580, which may also be caused by digitization, from approximately 0 to 40 between a relative light from approximately 0 to 1. The increase is approximately logarithmic.

[0261] Consequently, the inverse pixel response in the gain-controlled time measurement 581 is lower across the depicted range of relative light from 0 to 1. Furthermore, the inverse pixel response of the gain-controlled time measurement 581 still is a useful signal at a higher relative light, particularly over a relative light of approximately 0.5 as the inverse pixel response of the time measurement 580 is outside the depicted range of the inverse pixel response. Therefore, the dynamic range of the gain-controlled time measurement 581 performed by a gain-controlled imaging device according to an embodiment is higher.

[0262] Fig. 19c is graph comparing an inverse normalized pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16. Depicted is a graph showing an inverse normalized pixel response on the y-axis in relative units from 0 to 1 over the relative light from 0 to 1, which is the light received by the photodiode of the respective imaging devices.

[0263] The inverse normalized pixel response of the time measurement 580 increases in steps, which may be caused by digitization, from approximately 0 to 1 between a relative light from approximately 0 to 0.5. Thereafter, the inverse normalized pixel response of the time measurement 580 is outside the depicted range of the inverse normalized pixel response.

[0264] The inverse normalized pixel response of the gain-controlled time measurement 581 increases from approximately 0 to 1 between a relative light from approximately 0 to 1. The increase is approximately logarithmic.

[0265] There are two graphs of the inverse normalized pixel response of the gain-controlled time measurement 581. One increases in a smooth graph and is obtained with the analog gain- controlled imaging device of Fig. 10 and 11, the other increases in smaller steps than the steps of the inverse normalized pixel response of the time measurement 580, which may also be caused by digitization, and is obtained with the gain-controlled imaging device of Fig. 13 to 16.

[0266] Consequently, the inverse normalized pixel response in the gain-controlled time measurement 581 is lower across the depicted range of relative light from 0 to 1. Furthermore, the inverse normalized pixel response of the gain-controlled time measurement 581 still is a useful signal at a higher relative light, particularly over a relative light of approximately 0.5 as the inverse normalized pixel response of the time measurement 580 is outside the depicted range of the inverse normalized pixel response. Therefore, the dynamic range of the gain-controlled time measurement 581 performed by a gain-controlled imaging device according to an embodiment is higher.

[0267] As the relative light increased, all the graphs of Fig. 19a to 19c depict gain-controlled measurement with a flatter response. In the relative light range from 0 to 1 the sweet spot with the good dynamic is more visible.

[0268] Fig. 20a is graph comparing a pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16.

[0269] Depicted is a graph showing a pixel response on the y-axis in relative units from 0 to 0.5 over the relative light from 0 to 100, which is the light received by the photodiode of the respective imaging devices. Further depicted are the pixel response of a time measurement 580 without gain control and the pixel response of a gain-controlled time measurement 581 performed by a gain-controlled imaging device according to an embodiment.

[0270] The pixel response of the time measurement 580 and gain-controlled time measurement 581 cannot be separated from the y-axis and x-axis for higher pixel responses and at higher relative lights because the range of relative light is larger than depicted in Fig. 18a.

[0271] Because of the larger range of relative light, the pixel response of the time measurement 580 is only visible in the lower-left comer around the origin point.

[0272] The pixel response of the gain-controlled time measurement 581 drops from approximately 0.05 to 0 between a relative light from approximately 0 to 100. The drop is also asymptotic.

[0273] Consequently, the pixel response in the gain-controlled time measurement 581 is higher across the depicted range of relative light from 0 to 100. Furthermore, the pixel response of the gain- controlled time measurement 581 still is a useful signal at a higher relative lights. Therefore, the dynamic range of the gain-controlled time measurement 581 performed by a gain-controlled imaging device according to an embodiment is higher.

[0274] Fig. 20b is a graph comparing an inverse pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16.

[0275] Depicted is a graph showing an inverse pixel response on the y-axis in relative units from 0 to 1000 over the relative light from 0 to 100, which is the light received by the photodiode of the respective imaging devices.

[0276] The inverse pixel response of the time measurement 580 increases almost parallel to the y-axis from approximately 0 to 1000 and thereafter is outside the depicted range of the inverse pixel response.

[0277] The inverse pixel response of the gain-controlled time measurement 581 increases from approximately 0 to 300 between a relative light from approximately 0 to 100. The increase is approximately logarithmic.

[0278] There are two graphs of the inverse pixel response of the gain-controlled time measurement 581. One increases in a smooth graph and is obtained with the analog gain-controlled imaging device of Fig. 10 and 11, the other increases in smaller steps than the steps of the inverse pixel response of the time measurement 580, which may also be caused by digitization, and is obtained with the gain-controlled imaging device of Fig. 13 to 16.

[0279] Consequently, the inverse pixel response in the gain-controlled time measurement 581 is lower across the depicted range of relative light from 0 to 10. Furthermore, the inverse pixel response of the gain-controlled time measurement 581 still is a useful signal at a higher relative light, particularly where the inverse pixel response of the time measurement 580 is outside the depicted range of the inverse pixel response. Therefore, the dynamic range of the gain-controlled time measurement 581 performed by a gain-controlled imaging device according to an embodiment is higher.

[0280] Fig. 20c is graph comparing an inverse normalized pixel response of a time measurement without gain control as performed with an imaging device of Fig. 4, 5, 8 and 9 with a time measurement performed with a gain-controlled imaging device according to the embodiments of Fig. 10, 11 and 13 to 16.

[0281] Depicted is a graph showing an inverse normalized pixel response on the y-axis in relative units from 0 to 1 over the relative light from 0 to 100, which is the light received by the photodiode of the respective imaging devices.

[0282] The inverse normalized pixel response of the time measurement 580 increases almost parallel to the y-axis from approximately 0 to 1, thereafter the inverse normalized pixel response of the time measurement 580 is outside the depicted range of the inverse normalized pixel response.

[0283] The inverse normalized pixel response of the gain-controlled time measurement 581 increases from approximately 0 to 1 between a relative light from approximately 0 to 100. The increase is approximately logarithmic.

[0284] There are two graphs of the inverse normalized pixel response of the gain-controlled time measurement 581. One increases in a smooth graph and is obtained with the analog gain- controlled imaging device of Fig. 10 and 11, the other increases in smaller steps than the steps of the inverse normalized pixel response of the time measurement 580, which may also be caused by digitization, and is obtained with the gain-controlled imaging device of Fig. 13 to 16.

[0285] Consequently, the inverse normalized pixel response in the gain-controlled time measurement 581 is lower across the depicted range of relative light from 0 to 10. Furthermore, the inverse normalized pixel response of the gain-controlled time measurement 581 still is a useful signal at a higher relative light, particularly over a relative light of approximately 1 as the inverse normalized pixel response of the time measurement 580 is outside the depicted range of the inverse normalized pixel response. Therefore, the dynamic range of the gain-controlled time measurement 581 performed by a gain-controlled imaging device according to an embodiment is higher.

[0286] As the relative light increased, all the graphs of Fig. 20a to 20c depict gain-controlled measurement with a flatter response. In the relative light range from 0 to 100 the dynamics range is very high. However, the digital version clearly shows quantization effects.

[0287] Fig. 21a depicts an image of an inside scene in the foreground and an outside scene in the background.

[0288] The image 600 depicts an inside scene comprising objects such as a table and chairs 601, a bowl 602 and a sofa 603. Through windows 604 and 605 the outside scenes 606 and 607 are not visible because they are overexposed in the image 600.

[0289] Fig. 21b depicts an image of an inside scene in the foreground and an outside scene in the background with a lower exposure time as the image of fig. 21a.

[0290] The image 600 depicts an inside scene comprising objects such as a table and chairs 601, a bowl 602 and a sofa 603. The inside scene is depicted as hatched, since the inside scene is underexposed. Through windows 604 and 605 the outside scenes 606 and 607 are visible because they are well exposed in the image 600.

[0291] In Fig. 21a and 21b a problem with the exposure time of cameras taking images is displayed, namely the bright parts of a scene (outside scene) may be overexposed and / or lower light parts of a scene (inside scene) may be underexposed if they are imaged with the same exposure time. Thus, it is difficult to image such scenes with the same exposure time. This is because cameras my not be able to cover the full dynamic range of a scene, which may be the indoor and outdoor scene of Fig. 21a and b or any other scene with a high dynamic range, such that areas at opposite ends of the dynamic range of a scene (indoor and outdoor) are simultaneously visible with good contrast (either too dark or too bright, saturated).

[0292] This problem may be solved by measuring time information in addition to a signal level (e.g. an accumulated voltage signal), for example by measuring a gradient of a signal level over time. The problem may further be solved by (a) feedback (loop) to the gain of the amplifier to achieve conversion of the signal level to a predetermined reference level, such as in the gain-controlled imaging devices according to an embodiment. Fig. 22a depicts an image of an inside scene and an outside scene with a lower exposure time of Fig. 21b.

[0293] In addition to the image of Fig. 21b, Fig. 22a also marks areas for a measurement of a signal level measured outside 609 and a signal level measured inside 608.

[0294] Fig. 22b is a diagram depicting a measured signal level over time.

[0295] The signal of the intensity outside 609 is a continuous graph and rises faster than the signal of the intensity inside 608, which is also a continuous graph.

[0296] The signal of the signal level measured outside 609 or the signal level measured inside 608 can also be measured and output discretely at several times as depicted in Fig. 23a or output once at a time that may be the end of an exposure time as depicted in Fig. 23b.

[0297] If an object is brighter, the measured signal level also grows faster. This is independent of the type of measurement, e.g. a voltage measurement, a time measurement or a gain-controlled time measurement.

[0298] Fig. 24 is a diagram depicting a derived signal over exposure time and the signal gradient of the measurement of Fig. 23a.

[0299] The gradient 612 can be calculated from the delta time 611 and the delta signal 610 of the measurement, as a division of delta signal 610 by delta time 611.

[0300] Instead of measuring and storing an intensity received by a pixel, a gradient of said pixel may be determined and stored, wherein the gradient is derived from the additional time measurement.

[0301] Fig. 25 a is a diagram of a gradient distribution of an image which may be used to correct the exposure of an image.

[0302] The diagram shows the relative frequency on the y-axis and the gradient on the x-axis.

[0303] The gradient distribution 613 has two peaks. This is typical for an image with high dynamic range. The peak at lower gradients is derived from the inside scene and its objects 601, 602, 603, 608. The peak at higher gradients is derived from the outside scene 606, 607, 609. Normal low dynamic range cameras can only image the inside scene or the outside scene with full contrast.

[0304] Normally to obtain an image that exposes both the inside scene 601, 602, 603, 608 and the outside scene 606, 607, 609 accurately at least two images may be taken and composed or the gradients of the outside scene 606, 607, 609 may be shifted along arrow 614 so that in an image both the outside scene 606, 607, 609 and the inside scene 601, 602, 603, 608 are exposed well, to obtain the exposure depicted in Fig. 25b. This exposure may also be changed by changing an exposure time the gradient is multiplied with to obtain an intensity of the pixel, for example in post-processing.

[0305] An interface may also allow a manipulation of the gradient, wherein a user may select an area (of interest) in an image, wherein the gradient from this area is manipulated or shifted to adjust the exposure in the area.

[0306] Further, the gradient may be shifted by the gain-control at a time of measurement and as the growth of the accumulated voltage signal is used to dynamically change the gain of the amplifier. Thus, the gain-controlled imaging device according to an embodiment achieves a higher dynamic rage.

[0307] Thus, storing of gradients as pixel values allows for better high dynamic rage imaging and manipulation in post-processing at the cost of more memory needed to store the gradients as floating-point numbers.

[0308] The imaging devices 400, 500a and 500b may be implemented in an array of pixels utilizing the photodiode of imaging devices 400, 500a and 500b as the photoconversion zone of at least a pixel of the array of pixels. The imaging devices 400, 500a and 500b may also be implemented such that they are the pixel circuit of all pixels in the pixel array.

[0309] In such a cases the components of the imaging devices 400, 500a and 500b such as for example a controller, a difference, a reference, a counter, an oscillator, an integration constant, a sample, an ADC, a buffer, a sequencer, a reset and a comparator may be implemented for an individual pixel, a row or column of pixels, a (2D) region of pixels, or globally for the entire array of pixels.

[0310] All units and entities described in this specification and claimed in the appended claims can, if not stated otherwise, be implemented as integrated circuit logic, for example on a chip, and functionality provided by such units and entities can, if not stated otherwise, be implemented by software.

[0311] In so far as the embodiments of the disclosure described above are implemented, at least in part, using software-controlled data processing apparatus, it will be appreciated that a computer program providing such software control and a transmission, storage or other medium by which such a computer program is provided are envisaged as aspects of the present disclosure.

[0312] Note that the present technology can also be configured as described below. <1> A gain-controlled solid-state imaging device (400, 500a, 500b), comprising a gain amplifier (302, 402, 502) configured to amplify the output of photodiode (301, 401, 501), circuitry configured to dynamically change the output of the amplifier (302, 402, 502) during exposure in response to a feedback signal.

[0313] <2> The gain-controlled solid-state imaging device (400, 500a, 500b) according to <1> further comprising an integrator (304, 404, 504) configured to integrate the dynamically changed output of the gain amplifier (302, 402, 502) to obtain an integration output.

[0314] <3> The gain-controlled solid-state imaging device (400, 500a, 500b) according to <2>, wherein the circuitry is configured to dynamically change the input gain of the gain amplifier (302, 402, 502) in response to the feedback signal.

[0315] <4> The gain-controlled solid-state imaging device (400, 500a, 500b) according to <3>, wherein the circuitry comprises a controller (313, 413, 513) configured to determine information indicative of a time passed since a beginning of exposure based on the integration output, determine the feedback signal based on the information indicative of a time passed since a beginning of exposure, and control the input gain of the gain amplifier (302, 402, 502) based on the feedback signal.

[0316] <5> The gain-controlled solid-state imaging device (400, 500a, 500b) according to <3>, comprising a comparison circuit (312, 412, 512) configured to compare the integration output with a predetermined reference signal to obtain a comparison result indicative of whether the integration output has reached a signal level of the reference signal, and the controller (313, 413, 513) configured to determine information indicative of a time passed since a beginning of exposure based on the comparison result.

[0317] <6> The gain controlled solid-state imaging device (400, 500a, 500b) according to <5>, wherein the controller (313, 413, 513) comprises a second integrator (304, 404, 504) configured to integrate the comparison result and to output an integration result as the information indicative of a time passed from a beginning of an exposure.

[0318] <7> The gain-controlled solid-state imaging device (400, 500a, 500b) according to <5>, comprising a sample circuit (308, 408, 508) configured to sample the information indicative of a time passed since a beginning of exposure when the comparison result indicates that the integration output has reached a signal level of the reference signal.

[0319] <8> The gain controlled solid-state imaging device (400, 500a, 500b) according to <5>, wherein the gain-controlled solid-state imaging device (400, 500a, 500b) is configured to determine a signal gradient based on the sampled the information indicative of a time passed since a beginning of exposure and the predetermined reference and store the signal gradient as a pixel value.

[0320] <9> The gain controlled solid-state imaging device (400, 500a, 500b) according to <2>, wherein the circuitry comprises a digital to analog converter (510a) configured to receive the output of the gain amplifier (302, 402, 502) and configured to provide an analogue signal to the integrator (304, 404, 504), wherein the digital to analog converter (510a) is controlled on the basis of the feedback signal.

[0321] <10> The gain-controlled solid-state imaging device (400, 500a, 500b) according to <9>, comprising a comparison circuit (312, 412, 512) configured to compare the integration output with a predetermined reference signal to obtain a comparison result indicative of whether the integration output has reached a signal level of the reference signal.

[0322] <11> The gain-controlled solid-state imaging device (400, 500a, 500b) according to <10>, wherein the circuitry comprises a controller (313, 413, 513) configured to determine information indicative of a time passed since a beginning of exposure, determine the feedback signal based on the information indicative of a time passed since a beginning of exposure, and control the digital to analog converter (510a) based on the feedback signal.

[0323] <12> The gain-controlled solid-state imaging device (400, 500a, 500b) according to <11>, wherein the controller (313, 413, 513) is configured to determine information indicative of a time passed since a beginning of exposure based on an oscillating signal provide by an oscillator (514).

[0324] <13> The gain-controlled solid-state imaging device (400, 500a, 500b) according to <11>, comprising a sample circuit (308, 408, 508) configured to sample the information indicative of a time passed since a beginning of exposure when the comparison result indicates that the integration output has reached a signal level of the reference signal.

[0325] <14> The gain controlled solid-state imaging device (400, 500a, 500b) according to <13>, wherein the gain-controlled solid-state imaging device (400, 500a, 500b) is configured to determine a signal gradient based on the sampled the information indicative of a time passed since a beginning of exposure and the predetermined reference and store the signal gradient as a pixel value.

[0326] <15> The gain controlled solid-state imaging device (400, 500a, 500b) according to <2>, wherein the circuitry comprises a pulse width modulator (510b) configured to receive the output of the gain amplifier (302, 402, 502) output and configured to provide a pulse width modulated signal to the integrator (304, 404, 504), wherein the pulse width modulator (510b) is controlled on the basis of the feedback signal.

[0327] <16> The gain-controlled solid-state imaging device (400, 500a, 500b) according to <15>, comprising a comparison circuit (312, 412, 512) configured to compare the integration output with a predetermined reference signal to obtain a comparison result indicative of whether the integration output has reached a signal level of the reference signal.

[0328] <17> The gain-controlled solid-state imaging device (400, 500a, 500b) according to <16>, wherein the circuitry comprises a controller (313, 413, 513) configured to determine information indicative of a time passed since a beginning of exposure, determine the feedback signal based on the information indicative of a time passed since a beginning of exposure, and control the pulse width modulator (510b) based on the feedback signal.

[0329] <18> The gain-controlled solid-state imaging device (400, 500a, 500b) according to <17>, wherein the controller (313, 413, 513) is configured to determine information indicative of a time passed since a beginning of exposure based on an oscillating signal provide by an oscillator (514).

[0330] <19> The gain-controlled solid-state imaging device (400, 500a, 500b) according to <17>, comprising a sample circuit (308, 408, 508) configured to sample the information indicative of a time passed since a beginning of exposure when the comparison result indicates that the integration output has reached a signal level of the reference signal.

[0331] <20> The gain controlled solid-state imaging device (400, 500a, 500b) according to <19>, wherein the gain-controlled solid-state imaging device (400, 500a, 500b) is configured to determine a signal gradient based on the sampled the information indicative of a time passed since a beginning of exposure and the predetermined reference and store the signal gradient as a pixel value.

[0332] <21> The gain controlled solid-state imaging device (400, 500a, 500b) according to any one of <1> to <20>, wherein the circuitry further comprises plurality of photodiodes (301, 401, 501), a plurality of gain amplifiers (302, 402, 502), wherein a signal of each photodiode (301, 401, 501) of the plurality of photodiodes (301, 401, 501) is amplified by a corresponding gain amplifier (302, 402, 502) of the plurality of gain amplifiers (302, 402, 502), and wherein the circuitry is configured to dynamically change the output of each gain amplifier (302, 402, 502) of the plurality of amplifiers (302, 402, 502) during exposure in response to a feedback signal. <22> A method for controlling a gain controlled solid-state imaging device (400, 500a, 500b), comprising amplifying, by a gain amplifier (302, 402, 502), the output of a photodiode (301, 401, 501), and dynamically changing the output of the gain amplifier (302, 402, 502) during exposure in response to a feedback signal.

[0333] <23> A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to <22>.

[0334] <24> A computer program comprising program code causing a computer to perform the method according to <22>, when being carried out on a computer.

[0335] <25> A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to anyone of <22> to be performed.

[0336] List of reference signs:

[0337] 100, 200, 300, 400, 500a, 500b imaging device

[0338] 101, 201, 301, 401, 501 Photodiode

[0339] 102, 202, 302, 402, 502 Amplifier

[0340] 103, 203, 303 Gain

[0341] 104, 204, 304, 404, 504 Integrator

[0342] 105, 205, 305, 405, 505 Reset

[0343] 106 Exposure time

[0344] 107, 207, 307, 407, 507 Sequencer

[0345] 108, 208, 308, 408, 508 Sample

[0346] 109, 209, 409 Analog-to-Digital-Converter

[0347] 211, 311, 411, 415, 511, 516 Reference

[0348] 212, 312, 412, 414, 512 Comparator (Difference)

[0349] 213 Integrator

[0350] 214 Constant

[0351] 309, 509 Buffer

[0352] 313, 413, 513 Counter (Controller) 314, 514 Oscillator

[0353] 510a Digital-to-Analog-Converter

[0354] 510b Pulse Width Modulator

[0355] 150, 250, 350, 450, 550 Operation method 580 Response Time Measurement

[0356] 581 Response Gain Control (analog / digital)

[0357] 600 Image

[0358] 601, 602, 603 Inside Scene (Objects)

[0359] 604, 605 Windows 606, 607 Outside Scene

[0360] 608 Intensity inside

[0361] 609 Intensity outside

[0362] 610 Delta Signal

[0363] 611 Delta Time 612 Gradient

[0364] 613 Gradient distribution

[0365] 614 Arrow (Gradient Shift)

Claims

CLAIMS1. A gain-controlled solid-state imaging device, comprising a gain amplifier configured to amplify the output of photodiode, and circuitry configured to dynamically change the output of the amplifier during exposure in response to a feedback signal.

2. The gain-controlled solid-state imaging device according to claim 1, further comprising an integrator configured to integrate the dynamically changed output of the gain amplifier to obtain an integration output.

3. The gain-controlled solid-state imaging device according to claim 2, wherein the circuitry is configured to dynamically change the input gain of the gain amplifier in response to the feedback signal.

4. The gain-controlled solid-state imaging device according to claim 3, wherein the circuitry comprises a controller configured to determine information indicative of a time passed since a beginning of exposure based on the integration output, determine the feedback signal based on the information indicative of a time passed since a beginning of exposure, and control the input gain of the gain amplifier based on the feedback signal.

5. The gain-controlled solid-state imaging device according to claim 3, comprising a comparison circuit configured to compare the integration output with a predetermined reference signal to obtain a comparison result indicative of whether the integration output has reached a signal level of the reference signal, and the controller configured to determine information indicative of a time passed since a beginning of exposure based on the comparison result.

6. The gain controlled solid-state imaging device according to claim 5, wherein the controller comprises a second integrator configured to integrate the comparison result and to output an integration result as the information indicative of a time passed from a beginning of an exposure.

7. The gain-controlled solid-state imaging device according to claim 5, comprising a sample circuit configured to sample the information indicative of a time passed since abeginning of exposure when the comparison result indicates that the integration output has reached a signal level of the reference signal.

8. The gain controlled solid-state imaging device according to claim 4, wherein the gain- controlled solid-state imaging device is configured to determine a signal gradient based on the sampled the information indicative of a time passed since a beginning of exposure and the predetermined reference and store the signal gradient as a pixel value.

9. The gain controlled solid-state imaging device according to claim 2, wherein the circuitry comprises a digital to analogue converter configured to receive the output of the gain amplifier and configured to provide an analogue signal to the integrator, wherein the digital to analog converter is controlled on the basis of the feedback signal.

10. The gain-controlled solid-state imaging device according to claim 9, comprising a comparison circuit configured to compare the integration output with a predetermined reference signal to obtain a comparison result indicative of whether the integration output has reached a signal level of the reference signal.

11. The gain-controlled solid-state imaging device according to claim 10, wherein the circuitry comprises a controller configured to determine information indicative of a time passed since a beginning of exposure, determine the feedback signal based on the information indicative of a time passed since a beginning of exposure, and control the digital to analogue converter based on the feedback signal.

12. The gain-controlled solid-state imaging device according to claim 11, wherein the controller is configured to determine information indicative of a time passed since a beginning of exposure based on an oscillating signal provide by an oscillator.

13. The gain-controlled solid-state imaging device according to claim 11, comprising a sample circuit configured to sample the information indicative of a time passed since a beginning of exposure when the comparison result indicates that the integration output has reached a signal level of the reference signal.

14. The gain controlled solid-state imaging device according to claim 13, wherein the gain- controlled solid-state imaging device is configured to determine a signal gradient based on the sampled the information indicative of a time passed since a beginning of exposure and the predetermined reference and store the signal gradient as a pixel value.

15. The gain controlled solid-state imaging device according to claim 2, wherein the circuitry comprises a pulse width modulator configured to receive the output of the gain amplifier and configured to provide a pulse width modulated signal to the integrator, wherein the pulse width modulator is controlled on the basis of the feedback signal.

16. The gain-controlled solid-state imaging device according to claim 15, comprising a comparison circuit configured to compare the integration output with a predetermined reference signal to obtain a comparison result indicative of whether the integration output has reached a signal level of the reference signal.

17. The gain-controlled solid-state imaging device according to claim 16, wherein the circuitry comprises a controller configured to determine information indicative of a time passed since a beginning of exposure, determine the feedback signal based on the information indicative of a time passed since a beginning of exposure, and control the pulse width modulator based on the feedback signal.

18. The gain-controlled solid-state imaging device according to claim 17, wherein the controller is configured to determine information indicative of a time passed since a beginning of exposure based on an oscillating signal provide by an oscillator.

19. The gain-controlled solid-state imaging device according to claim 17, comprising a sample circuit configured to sample the information indicative of a time passed since a beginning of exposure when the comparison result indicates that the integration output has reached a signal level of the reference signal.

20. The gain controlled solid-state imaging device according to claim 19, wherein the gain- controlled solid-state imaging device is configured to determine a signal gradient based on the sampled the information indicative of a time passed since a beginning of exposure and the predetermined reference and store the signal gradient as a pixel value.

21. The gain controlled solid-state imaging device according to claim 1, wherein the circuitry further comprises plurality of photodiodes, a plurality of gain amplifiers, wherein a signal of each photodiode of the plurality of photodiodes is amplified by a corresponding gain amplifier of the plurality of gain amplifiers, and wherein the circuitry is configured to dynamically change the output of each gain amplifier of the plurality of amplifiers during exposure in response to a feedback signal.

22. A method for controlling a gain controlled solid-state imaging device, comprising amplifying, by a gain amplifier, the output of a photodiode, and dynamically changing the output of the gain amplifier during exposure in response to a feedback signal.

23. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to claim 22.

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