An image sensor with adaptive tail current

Abstract

The application discloses an image sensor with adaptive tail current adjustment, comprising a pixel array for detecting and collecting photoelectric signals; a column bus corresponding to each pixel column of the pixel array for transmitting the photoelectric signals; a pixel tail current module electrically connected to the column bus for adaptively adjusting tail current according to register control signals and working tail current control signals, so that the total tail current size changes synchronously with the working main frequency of the image sensor; and a column-level circuit electrically connected to the output end of the column bus for reading out the photoelectric signals output by the output bus after processing by the tail current. Compared with the prior art, the application has higher adaptive adjustment accuracy, and comprehensively improves the working speed performance, power consumption performance and noise performance of the image sensor.

Description

Technical Field

[0001] This invention relates to the field of image sensor technology, and in particular to an image sensor with adaptive tail current adjustment. Background Technology

[0002] With the development of modern information society, image sensors are being used more and more widely in life, and their performance is becoming more and more powerful. Solid-state image sensors integrate photosensitive units on semiconductor substrates to form pixel arrays to acquire image information. According to the photoelectric conversion effect, reflected light from external objects shines on the pixel array, and the pixel units at corresponding positions on the pixel array convert photoelectric signals into electrical signals, process and store them according to their positional relationships, and output them to obtain an image.

[0003] Typical image sensors typically employ a two-dimensional array of rows and columns for pixel layout. In the column direction of the array, the pixel output stage is usually a source follower. Source followers on the same column bus usually share a common load current source. Due to the presence of parasitic resistance and capacitance on the column bus, the noise characteristics and response speed characteristics of the source follower are affected, thereby affecting the image quality and the frame rate of the image sensor. This effect is particularly pronounced when the size of the pixel array operating simultaneously is large (such as global shutter image sensors, ultra-large scale image sensors, etc.) or when the operating frequency is high (such as high frame rate image sensors, etc.).

[0004] Currently, to improve the response speed of the column bus, the common method is to increase the load current and tail current of the source follower. However, this increases the chip's power consumption, especially noticeable in large-area image sensors. It also reduces the output swing of the pixel's original output signal, thus decreasing the pixel's dynamic range. Another common method is to use two load current sources, selecting different load current paths using external registers based on application testing conditions. While this method can achieve good imaging results, it is complex to debug and lacks flexibility. If the application scenario changes (such as changes in the operating clock or window size), the user needs to re-perform testing and analysis, manually adjusting the pixel load follower tail current to achieve the best imaging effect. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide an image sensor that adaptively adjusts the tail current, so as to solve the problems in the prior art that the increase in the image sensor number, the decrease in dynamic range, and the increase in the use of external register control caused by the increase in tail current.

[0006] To achieve the above objectives, the present invention provides an image sensor with adaptive tail current adjustment, comprising:

[0007] Pixel array, used to detect and acquire photoelectric signals;

[0008] The column bus is configured to correspond one-to-one with the pixel column of the pixel array and is used to transmit photoelectric signals;

[0009] Each pixel tail current module is electrically connected to the column bus in a one-to-one correspondence. It is used to adaptively adjust the tail current according to the register control signal and the operating tail current control signal, so that the total tail current magnitude changes synchronously with the operating frequency of the image sensor; and

[0010] Each of the column-level circuits is electrically connected to the output terminal of the column bus in a one-to-one correspondence, and is used to process and read out the photoelectric signal output from the output bus according to the tail current.

[0011] Furthermore, the pixel tail current module includes a preparatory tail current circuit electrically connected to the column bus and corresponding to a first end farther from the output end of the column bus, and a working tail current circuit electrically connected to the column bus and corresponding to a second end closer to the output end of the column bus. The preparatory tail current circuit is used to control the selected pixel row according to the register control signal, so that the magnitude of the first total tail current changes synchronously with the column bus load of the image sensor. The working tail current circuit is used to perform relevant timing control on the small tail current part according to the working tail current control signal, so that the magnitude of the second total tail current changes synchronously with the frame rate and window size of the image sensor.

[0012] Furthermore, the pre-tail current circuit includes a pre-tail current array electrically connected to the first end of the column bus and a register control sub-circuit electrically connected to the pre-tail current array. The register control sub-circuit is used to generate a register control signal according to the window size of the image sensor. The pre-tail current array is used to control the selected pre-tail current array according to the register control signal and adaptively adjust the first total tail current output by the pre-tail current array so that the magnitude of the first total tail current changes synchronously with the column bus load.

[0013] Furthermore, the pre-tail current array includes K first tail current branches connected in parallel in the column bus. Each first tail current branch includes a first gating control switch and a first tail current source connected in series. The first input terminal of the first gating control switch is electrically connected in the column bus, and the second input terminal of the first gating control switch is electrically connected to the corresponding output terminal of the register control sub-circuit. Wherein, K = log2M, M is the number of rows in the pixel array, and M is a natural number.

[0014] Furthermore, the magnitudes of the tail currents of the K first tail current branches are:

[0015] I i ={2 0 *I,2 1 *I,...,2 i-1 *I};

[0016] Among them, I i Let i be the magnitude of the tail current of the first tail current branch, i = 1, 2, ..., K, and I be the design matching current of the image sensor in the minimum row window mode.

[0017] Furthermore, the register control sub-circuit has row selection control signal output terminals that correspond one-to-one with the first tail current branch, and each row selection control signal output terminal is electrically connected to the second input terminal of the corresponding first gating control switch; the value output by the row selection control signal output terminal changes in binary according to the window size of the image sensor to select the corresponding first tail current branch.

[0018] Furthermore, the working tail current circuit includes a working tail current array electrically connected to the second end of the column bus and a working tail current control sub-circuit electrically connected to the working tail current array. The working tail current control sub-circuit is used to generate a working tail current control signal according to the column readout clock accessed by the image sensor and the applied periodic enable signal. The working tail current array is used to control the selected pixel row according to the working tail current control signal and adaptively adjust the second total tail current output by the working tail current array so that the magnitude of the second total tail current changes synchronously with the working frequency of the image sensor.

[0019] Furthermore, the working tail current array includes Q second tail current branches connected in parallel in the column bus. Each second tail current branch includes a second gating control switch and a second tail current source connected in series. The first input terminal of the second gating control switch is electrically connected to the column bus, and the second input terminal of the second gating control switch is electrically connected to the corresponding output terminal of the working tail current control sub-circuit. Wherein, Q = CLK max / CLK min CLK max CLK is the highest clock speed for an image sensor. min This is the lowest clock speed for the image sensor.

[0020] Furthermore, the magnitude of the tail current in each of the Q second tail current branches is I. min , among which, I min The design matching current for the lowest operating frame rate of the image sensor.

[0021] Furthermore, the working tail current control sub-circuit includes an AND gate control unit 521 and a serial-to-parallel conversion unit electrically connected to the output terminal of the AND gate control unit 521. The first input terminal and the second input terminal of the AND gate control unit 521 are respectively connected to the column readout clock and the applied periodic enable signal. The serial-to-parallel conversion unit has a second gating control signal output terminal corresponding to the second tail current branch. Each second gating control signal output terminal is electrically connected to the second input terminal of the corresponding first gating control switch.

[0022] This invention controls the timely operation and shutdown of the pre-sampling tail current circuit and the working tail current circuit. The pre-sampling tail current circuit is turned on only before signal sampling and turned off during the sampling phase, while the working tail current circuit operates normally throughout the signal readout phase. This switching combination of operating modes reduces the overall power consumption of the image sensor. Furthermore, the pre-sampling tail current circuit's pre-sampling discharge of charge on the column bus improves the setup time of subsequent pixel output signals. Both the pre-sampling and working tail current circuits utilize tail current arrays coupled to the column bus. Register control signals and working tail current control signals directly correlate the tail current magnitude with the total number of pixels on the column bus and the chip's operating speed. The total tail current of both the pre-sampling and working tail current arrays is adaptively adjusted based on the image sensor's frame rate and window size, pulling the column bus voltage to a suitable level, thereby improving the image sensor's noise characteristics and response speed. Moreover, by flexibly combining different tail current branches, the same image sensor can adapt to different operating scenarios and modes, expanding its dynamic range. Attached Figure Description

[0023] Figure 1 This is a block diagram of the image sensor with adaptive tail current adjustment according to the present invention.

[0024] Figure 2 The structural block diagram for preparing the tail current circuit.

[0025] Figure 3 This is a block diagram of the register control sub-circuit.

[0026] Figure 4 This is a block diagram of the working tail current circuit.

[0027] Figure 5 This is a block diagram of the working tail current control sub-circuit.

[0028] The diagrams in the instruction manual are labeled as follows:

[0029] Pixel array 1, column bus 2, column-level circuit 3, pre-tail current circuit 4, pre-tail current array 41, first tail current branch 411, first gating control switch 412, first tail current source 413, register control sub-circuit 42, working tail current circuit 5, working tail current array 51, second tail current branch 511, second gating control switch 512, second tail current source 513, working tail current control sub-circuit 52, AND gate control unit 521, serial-to-parallel conversion unit 522. Detailed Implementation

[0030] The following detailed description illustrates the specific implementation methods:

[0031] Example

[0032] like Figure 1 The diagram shows a structural block diagram of an image sensor with adaptive tail current adjustment according to the present invention. The image sensor with adaptive tail current adjustment of the present invention includes a pixel array 1, a column bus 2, pixel tail current modules, and a column-level circuit 3. The pixel array 1 can detect and acquire photoelectric signals. The column bus 2 is configured one-to-one with the pixel columns of the pixel array 1, and can transmit the photoelectric signals acquired by the pixel array 1. The pixel tail current modules are electrically connected one-to-one to the column bus 2, and can generate corresponding register control signals and working tail current control signals, and adaptively adjust the tail current according to the register control signals and working tail current control signals, so that the total tail current changes synchronously with the working frequency of the image sensor, realizing adaptive adjustment of the tail current. The column-level circuit 3 is electrically connected one-to-one to the output terminal of the column bus 2, and can process and read out the photoelectric signals output by the output bus according to the tail current. In this embodiment, the pixel array 1 includes M*N pixels, where M is the number of rows of the pixel array 1, N is the number of columns of the pixel array 1, and both M and N are natural numbers. N columns of pixels correspond to N column buses 2, and each column of pixels shares one column bus 2 to adjust the magnitude of the connected tail current so that it can be adaptively adjusted according to the frame rate of the image sensor and the window size.

[0033] The pixel tail current module includes a preparatory tail current circuit 4 electrically connected to the column bus 2 and corresponding to a first end farther from the output end of the column bus 2, and a working tail current circuit 5 electrically connected to the column bus 2 and corresponding to a second end closer to the output end of the column bus 2. In this embodiment, the first end of the column bus 2 corresponds to the signal input end of the column bus 2, and the second end of the column bus 2 corresponds to the signal output end of the column bus 2. The preparatory tail current circuit 4 only operates before the sampling of the photoelectric signal and is turned off during sampling to pre-discharge the photoelectric signal remaining in the previous sampling cycle of the column bus 2, preparing for the signal sampling work of the current sampling cycle, thereby improving the establishment time of the pixel output signal. Specifically, the preparatory tail current circuit 4 generates a register control signal according to the window size of the image sensor and controls the selected pixel row according to the register control signal, so that when the window size of the image sensor changes and causes a change in the load of the column bus 2, the first total tail current I corresponding to the first end of the column bus 2 increases. total1 The magnitude of the tail current can change synchronously with the load of column bus 2. The working tail current circuit 5 operates normally throughout the signal readout phase, thereby achieving adaptive adjustment of the tail current; specifically, the working tail current circuit 5 generates a working tail current control signal based on the column readout clock and the applied periodic enable signal connected to the image sensor, and controls the selected pixel row according to the working tail current control signal, so that the second total tail current I corresponding to the second end of the column bus 2 of the image sensor is obtained. total2 Its size changes synchronously with the operating frequency of the image sensor.

[0034] like Figure 2 As shown, the pre-tail current circuit 4 includes a pre-tail current array 41 electrically connected to the first end of the column bus 2 and a register control sub-circuit 42 electrically connected to the pre-tail current array 41. The register control sub-circuit 42 has a first gating control signal output terminal corresponding to the pre-tail current array 41, so as to output a first gating control signal to control the pre-tail current array 41 according to the window size, thereby controlling the conduction of the pixel row corresponding to the pixel array 1, and realizing the first total tail current I. total1 Its adaptive adjustment allows it to change synchronously with the load changes of column bus 2.

[0035] The pre-tail current array 41 includes K first tail current branches 411 connected in parallel in the column bus 2. Each first tail current branch 411 includes a first gating control switch 412 and a first tail current source 413 connected in series. The first gating control switch 412 has a first input terminal for connecting the first tail current branch 411 to the column bus 2 and a second input terminal for connecting the first tail current branch 411 to the corresponding first gating control signal output terminal of the register control sub-circuit 42. When the first gating control switch 412 is placed at its first input terminal, the corresponding first tail current branch 411 is turned on. When the first gating control switch 412 is placed at its second input terminal, the corresponding first tail current branch 411 is turned off, and the first total tail current I... total1 The first total tail current I is determined by the tail current of each first tail current branch 411 connected to (i.e. turned on) the column bus 2. The K first tail current branches 411 can be combined according to the window size of the image sensor under the control of the register control sub-circuit 42, so as to adjust the first total tail current I by the number of connected first tail current branches 411. total1 The size is adjusted to adapt to changes in the column bus 2 load caused by changes in window size.

[0036] In this embodiment, since the number of rows of pixel array 1 on each column bus 2 is M, there are M combinations required to select and control the K first tail current branches 411. Therefore, the number K of the first tail current branches 411 is expressed as:

[0037] K = log₂M (1)

[0038] Where: K is the number of the first tail current branch 411, M is the number of rows of pixel array 1, and M is a natural number.

[0039] The magnitudes of the tail currents of the K first tail current branches 411 are expressed as follows:

[0040] I i ={2 0 *I,2 1 *I,...,2 i-1 *I} (2)

[0041] Among them, I i Let I be the magnitude of the tail current of the first tail current branch 411, i = 1, 2, ..., K, and let I be the design matching current of the image sensor in the minimum row window mode. The design target value of I is to pull the voltage of column bus 2 to the half-saturation level of the pixel output voltage.

[0042] like Figure 3As shown, to control each first tail current branch 411, the register control sub-circuit 42 has a first gating control signal output terminal corresponding to each of the first tail current branches 411. Each first gating control signal output terminal is electrically connected to the second input terminal of the corresponding first gating control switch 412 to output K register control signals Ctrl1 to Ctrl1. K The control circuit 42 controls the "on / off" state of the first gating control switch 412 (i.e., setting it to the first input terminal or the second input terminal). Specifically, the register control sub-circuit 42 uses a K-bit register adapted to the pre-tail current array 41, which has K first gating control signal output terminals. K is the number of rows in the window of the image sensor as input. The K first gating control signal output terminals can output K register control signals to select the K first tail current branches 411. Ctrl1 corresponds to selecting the first first tail current branch 411 (i.e., the current is 2). 0 *I corresponds to the first tail current branch 411), Ctrl K Correspondingly select the Kth first tail current branch 411 (i.e., the current is 2) i-1 *I corresponds to the first tail current branch 411).

[0043] In this embodiment, the value output by the first gating control signal output terminal (i.e., the K-channel register control signal is represented as Ctrl1 to Ctrl) K The first tail current branch 411 is selected based on the binary change of the window size of the image sensor, thereby realizing the first total tail current I output by the tail current array 41 when the load of the column bus 2 changes due to the change of the window size. total1 Its size can change synchronously with the complex changes in column bus 2.

[0044] like Figure 4 As shown, the working tail current circuit 5 includes a working tail current array 51 electrically connected to the second end of the column bus 2 and a working tail current control sub-circuit 52 electrically connected to the working tail current array 51. The working tail current control sub-circuit 52 has a second gating control signal output terminal corresponding to the working tail current array 51, so as to generate a working tail current control signal according to the column readout clock and the applied periodic enable signal connected to the image sensor, thereby controlling the conduction of the pixel row corresponding to the pixel array 1, and realizing the second total tail current I. total2 The adaptive adjustment makes the second total tail current I total2 Its size changes synchronously with the operating frequency of the image sensor.

[0045] The working tail current array 51 includes Q second tail current branches 511 connected in parallel in the column bus 2. Each second tail current branch 511 includes a second gating control switch 512 and a second tail current source 513 connected in series. The second gating control switch 512 has a first input terminal for connecting the second tail current branch 511 to the column bus 2 and a second input terminal for connecting the second tail current branch 511 to the corresponding second gating control signal output terminal of the working tail current control sub-circuit 52. When the second gating control switch 512 is placed at its first input terminal, the corresponding second tail current branch 511 is turned on. When the second gating control switch 512 is placed at its second input terminal, the corresponding second tail current branch 511 is turned off, and the second total tail current I... total2 The number of the Q second tail current branches 511 connected to the column bus 2 can be adjusted according to the change of the working main frequency of the image sensor under the control of the working tail current control sub-circuit 52, thereby adapting to the change of the working main frequency.

[0046] In this embodiment, the number Q of the second tail current branch 511 is determined by the operating frequency of the image sensor, and the number Q of the second tail current branch 511 is expressed as:

[0047] Q = CLK max / CLK min (3)

[0048] Among them: CLK max CLK is the highest clock speed for an image sensor. min This is the lowest clock speed for the image sensor.

[0049] The magnitude of each tail current in the Q second tail current branches 511 is I. min (where I) min (Design matching current for the lowest operating frame rate of the image sensor).

[0050] like Figure 5As shown, the working tail current control sub-circuit 52 includes an AND gate control unit 521 and a serial-to-parallel conversion unit 522 electrically connected to the output terminal of the AND gate control unit 521. The AND gate control unit 521 has a first input terminal and a second input terminal for external input signals and an output terminal electrically connected to the serial-to-parallel conversion unit 522. The first and second input terminals of the AND gate control unit 521 are respectively connected to the column readout clock CLK and the externally applied fixed-period enable signal EN. The AND gate control unit 521 can perform an AND operation on the column readout clock CLK and the fixed-period enable signal EN and then transmit the result to the serial-to-parallel conversion unit 522 for conversion. The serial-to-parallel conversion unit 522 has a second gating control signal output terminal corresponding one-to-one with the second tail current branch 511. Each second gating control signal output terminal is electrically connected to the second input terminal of the corresponding second gating control switch 512, so as to output Q-channel working tail current control signals Ctrl1 to Ctrl2. Q The second selection control switch 512 is controlled to "on / off". Specifically, the AND gate control unit 521 performs an AND operation on the column readout clock and the fixed-period enable signal EN to obtain an AND signal. The AND signal is transmitted from the output of the AND gate control unit 521 to the serial-to-parallel conversion unit 522. The serial-to-parallel conversion unit 522 can convert the AND signal into q parallel pulses (where q is the number of output parallel pulses, which is also the number of second tail current branches 511 connected to the column bus 2, q≤Q), thereby selecting q of the Q second tail current branches 511 to realize that when the operating frequency of the image sensor changes, the second total tail current I output by the operating tail current circuit 5 is... total2 Its size can automatically change with the operating frequency.

[0051] The adaptive tail current adjustment image sensor of the present invention introduces row selection control signal, column readout clock and fixed period enable signal at the same time, so that the adjustment of the total tail current is directly related to the number of pixels on column bus 2 and the operating frequency of the image sensor, thereby adaptively adjusting to a suitable tail current size to pull the voltage on column bus 2 to a suitable voltage level, so that the same image sensor can be used flexibly in various application scenarios and working modes.

Claims

1. An image sensor with adaptive tail current adjustment, characterized in that, include: Pixel array, used to detect and acquire photoelectric signals; The column bus is configured to correspond one-to-one with the pixel column of the pixel array and is used to transmit photoelectric signals; The pixel tail current module is electrically connected to the column bus in a one-to-one correspondence. It is used to adaptively adjust the tail current according to the register control signal and the working tail current control signal, so that the total tail current changes synchronously with the working frequency of the image sensor. as well as The column-level circuits are electrically connected one-to-one to the output terminals of the column bus, and are used to process and read out the photoelectric signals output from the output bus according to the tail current. The pixel tail current module includes a preparatory tail current circuit electrically connected to the column bus and corresponding to a first end farther from the output end of the column bus, and a working tail current circuit electrically connected to the column bus and corresponding to a second end closer to the output end of the column bus. The preparatory tail current circuit is used to control the selected pixel row according to the register control signal, so that the magnitude of the first total tail current changes synchronously with the column bus load of the image sensor. The working tail current circuit is used to perform relevant timing control on the small tail current part according to the working tail current control signal, so that the magnitude of the second total tail current changes synchronously with the frame rate and window size of the image sensor. The preparatory tail current circuit is turned on before signal sampling and turned off during the signal sampling stage, while the working tail current circuit works normally throughout the entire signal readout stage.

2. The image sensor with adaptive tail current adjustment according to claim 1, characterized in that, The pre-tail current circuit includes a pre-tail current array electrically connected to the first end of the column bus and a register control sub-circuit electrically connected to the pre-tail current array. The register control sub-circuit is used to generate a register control signal according to the window size of the image sensor. The pre-tail current array is used to control the selected pre-tail current array according to the register control signal and adaptively adjust the first total tail current output by the pre-tail current array so that the magnitude of the first total tail current changes synchronously with the column bus load.

3. The image sensor with adaptive tail current adjustment according to claim 2, characterized in that, The pre-tail current array includes K first tail current branches connected in parallel in the column bus. Each first tail current branch includes a first gating control switch and a first tail current source connected in series. The first input terminal of the first gating control switch is electrically connected to the column bus, and the second input terminal of the first gating control switch is electrically connected to the corresponding output terminal of the register control sub-circuit. Wherein, K = log2M, M is the number of rows in the pixel array, and M is a natural number.

4. The image sensor with adaptive tail current adjustment according to claim 3, characterized in that, The magnitudes of the tail currents of the K first tail current branches are: I i ={2 0 *I,2 1 *I,...,2 i-1 *I}; Among them, I i Let i be the magnitude of the tail current of the first tail current branch i, where i = 1, 2, ..., K, and I be the design matching current of the image sensor in the minimum row window mode.

5. The image sensor with adaptive tail current adjustment according to claim 3, characterized in that, The register control sub-circuit has a first gating control signal output terminal that corresponds one-to-one with the first tail current branch. Each first gating control signal output terminal is electrically connected to the second input terminal of the corresponding first gating control switch. The value output by the first gating control signal output terminal changes in binary according to the window size of the image sensor to select the corresponding first tail current branch.

6. The image sensor with adaptive tail current adjustment according to claim 1, characterized in that, The working tail current circuit includes a working tail current array electrically connected to the second end of the column bus and a working tail current control sub-circuit electrically connected to the working tail current array. The working tail current control sub-circuit is used to generate a working tail current control signal according to the column readout clock and the applied periodic enable signal connected to the image sensor. The working tail current array is used to control the selected pixel row according to the working tail current control signal and adaptively adjust the second total tail current output by the working tail current array so that the magnitude of the second total tail current changes synchronously with the working frequency of the image sensor.

7. The image sensor with adaptive tail current adjustment according to claim 6, characterized in that, The operating tail current array includes Q second tail current branches connected in parallel in the column bus. Each second tail current branch includes a second gating control switch and a second tail current source connected in series. The first input terminal of the second gating control switch is electrically connected to the column bus, and the second input terminal of the second gating control switch is electrically connected to the corresponding output terminal of the operating tail current control sub-circuit. Wherein, Q=CLK max / CLK min CLK max CLK is the highest clock speed for an image sensor. min This is the lowest clock speed for the image sensor.

8. The image sensor with adaptive tail current adjustment according to claim 7, characterized in that, The magnitude of the tail current in each of the Q second tail current branches is I. min , among which, I min The design matching current for the lowest operating frame rate of the image sensor.

9. The image sensor with adaptive tail current adjustment according to claim 7, characterized in that, The working tail current control sub-circuit includes an AND gate control unit 521 and a serial-to-parallel conversion unit electrically connected to the output terminal of the AND gate control unit 521. The first input terminal and the second input terminal of the AND gate control unit 521 are respectively connected to the column readout clock and the applied periodic enable signal. The serial-to-parallel conversion unit has a second gating control signal output terminal corresponding to the second tail current branch. Each second gating control signal output terminal is electrically connected to the second input terminal of the corresponding first gating control switch.

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