CN1992783A - Image sensor, readout circuit of image sensor and analog/digital conversion method thereof - Google Patents

Abstract

The invention discloses an image sensor, a reading circuit of the image sensor and an analog/digital conversion method thereof, which are mainly characterized in that a column analog image signal output by a sensing array is received by an amplifying and shifting unit, and then the column analog image signal is converted into a corresponding m-bit digital image signal by an m-bit analog/digital converter. Finally, an m-to-n bit conversion unit (m is larger than or equal to n) controlled by a k bit control signal is used to select continuous n bit signals in the m bit digital image signals to be output to the back-end processing circuit. Thus, the image distortion can be reduced, thereby obtaining the optimal dynamic range.

Description

Image sensor, readout circuit of image sensor and analog/digital conversion method thereof

technical field

The invention relates to a digital/analog conversion, in particular to a digital/analog conversion applied in a reading circuit of an image sensor.

Background technique

Complementary metal oxide semiconductor (CMOS) image sensors have been widely used in digital imaging devices such as video cameras, digital still cameras, camera phones, or video cameras. As shown in FIG. 1 , a conventional image sensor 1 generally includes a sensor array 10 (Sensor array), which includes sensor units (sensorunits, not shown) arranged in a matrix, and each sensor unit can sense The light source is controlled to transmit a row of analog image signals 23 sequentially in a row, and the row analog image signals 23 are then output to an amplification displacement unit 20 of a reading circuit 2 for signal operation processing of amplification and addition and subtraction, and then output an amplification displacement analog Video signal 24. Then, through an n-bit analog/digital converter 21, the amplified displacement analog image signal 24 is converted into a corresponding n-bit digital signal 25, and then transmitted to the back-end circuit (such as a digital signal processing unit (DSP)) for signal processing. deal with.

However, the above-mentioned traditional reading circuit may have the possibility of signal distortion when performing analog/digital signal conversion. As shown in Figure 2, the ideal image distribution range 23 will be 0-V1, and the actual image signal distribution range is more ideal. The distribution range of the voltage value has an error offset value ΔVoffset, which will cause the amplified displacement analog image signal 24 to have an actual image distribution range between Voffset～V2. After subtracting the correction signal Vp by an analog adder and subtractor (not shown in the figure) , although the distortion can be reduced, but the resolution of the analog adder and subtractor (not shown) is usually larger than the resolution of the analog/digital converter, so ΔVoffset≠Vp, although the error of the corrected image distribution line segment 26 is reduced, it is still difficult to The error is completely eliminated, so the image distribution is captured with poor resolution.

Contents of the invention

Therefore, the object of the present invention is to provide an image sensor, a reading circuit of the image sensor and an analog/digital conversion method thereof, which reduce the distortion of image signals and improve the resolution of image distribution and capture.

Therefore, the present invention provides a readout circuit of an image sensor, which is used to receive a row of analog image signals output by an image sensing array of the image sensor, and is characterized in that the readout circuit includes an amplifying displacement unit, an m-bit analog/digital converter, and an m-n-bit digital conversion unit. The amplification and displacement unit is used to amplify and modify the line of analog image signals to output an amplified and corrected analog signal; the m-bit analog/digital converter converts the amplified and corrected analog signal into a corresponding m-bit digital signal. The m-n-bit digital conversion unit converts the m-bit digital signal into an n-bit digital signal for output according to a k-bit control signal, wherein m≥n.

The present invention also provides an analog/digital conversion method applied to an image sensor. The image sensor can sense an image and output a row of analog image signals. It is characterized in that the method includes the following steps: first, the row Converting the analog image signal into a corresponding m-bit digital signal; and then controlling by a k-bit control signal, converting the m-bit digital signal into an n-bit digital signal for subsequent digital signal processing, wherein m≥n .

By means of the present invention, the continuous 1/2 ^mn region is arbitrarily selected from the input m-bit digital signal as an optimized n-bit digital signal output, which can not only reduce distortion, but also provide better dynamic capture Take the range.

Description of drawings

The present invention is described in detail below by preferred embodiment and accompanying drawing, in the accompanying drawing:

FIG. 1 is a schematic circuit diagram illustrating a conventional reading circuit of an image sensor;

FIG. 2 is a schematic diagram illustrating the difference between the ideal image distribution range, the actual image signal distribution range, and the corrected image distribution range;

3 is a schematic circuit diagram illustrating a preferred embodiment of a reading circuit of an image sensor of the present invention;

FIG. 4 is a schematic circuit diagram illustrating a detailed circuit block diagram of the amplifying displacement unit in FIG. 3; and

FIG. 5 is a schematic diagram illustrating an n-bit control signal controlling and selecting the output of the n-bit digital signal.

Detailed ways

The aforementioned and other technical contents, features and effects of the present invention will be clearly presented in the following detailed description of a preferred embodiment with reference to the drawings.

Referring to Fig. 3 to Fig. 4, it is a preferred embodiment of the reading circuit of the image sensor of the present invention, the reading circuit 4 of the image sensor 3 of the present embodiment includes an amplification displacement unit 41, an m-bit analog /digital converter 42 and an m to n-bit digital conversion unit 43, m≧n. The image sensor 3 further includes a sensor array 30 , and the sensor array 30 includes sensor units (sensor units, not shown) arranged in a matrix. Wherein, each sensing unit can sense the light source and transmit a corresponding row analog image signal 23 in a row under control.

The amplification and displacement unit 41 is used for receiving the line analog image signal 23 transmitted from the sensor array 30 and outputting an amplification and correction analog signal 24 after processing such as amplification, addition and subtraction. As shown in FIG. 4, the amplification displacement unit 41 includes a programmable gain amplifier 410 and an adder/subtractor 411, wherein the programmable gain amplifier 410 is used to amplify the line analog video signal 23 to an amplification with a predetermined gain. Analog signal 230 . The adder/subtractor 411 receives the offset calculated by the logic unit 50 in the back-end circuit (such as the digital signal processing (DSP) circuit 5 in FIG. After adding/subtracting the amplified analog signal 230, the amplified and corrected analog signal 24 is output.

Returning to FIG. 3, the m-bit analog/digital converter 42 is used to convert the amplified and corrected analog signal 24 into a corresponding m-bit digital signal 44, and then send it to the m-n-bit conversion unit 43, m ≥n. This m-to-n-bit conversion unit 43 will be controlled by an n-bit control signal 46 transmitted by the back-end circuit 5, (k=n in this embodiment), and select the continuous n-bit digital signal 45 (i.e. 2 ⁿ digital signal outputs).

For example, here n=10 is defined, assuming m=n+1=11, as shown in FIG. 5 , the output bit of the image sensor 3 is 10 bits. According to the above defined conditions, the m-bit digital signal 44 is an 11-bit digital signal, so the distribution range of the m-bit digital signal 44 is 0˜2047. The m to n bit conversion unit 43 is an 11 bit to 10 bit conversion unit. If the 10-bit control signal 46 received by the m-n-bit conversion unit 43 is, for example, 0..00 (binary)=0 (decimal), the m-n-bit conversion unit 43 will extract a range of 0 ~1023 10-bit digital signal 45 outputs. If the 10-bit control signal 46 is 00..1 (binary)=1 (decimal), the continuous 10-bit digital signal 45 from 1 to 1024 will be captured and output. By analogy, when the output signal is 11..1 (binary)=1023 (decimal), the continuous 10-bit digital signal 45 with a distribution range of 1023-2046 will be extracted and output.

In this way, the m-to-n-bit conversion unit 43 arbitrarily selects the continuous 1/2 ^mn area from the input m-bit digital signal 44 to output as the optimized n-bit digital signal D2, not only Distortion can be reduced and an optimized dynamic capture range can be provided.

Claims (8)

1. A readout circuit of an image sensor, which is used to receive a line of analog image signals output by an image sensor array of the image sensor, characterized in that the readout circuit includes: An amplification displacement unit, which is used to amplify and modify the line of analog image signals to output an enlarged and corrected analog signal; an m-bit analog/digital converter for converting the amplified corrected analog signal into a corresponding m-bit digital signal; and An m to n-bit digital conversion unit converts the m-bit digital signal into an n-bit digital signal for output according to a k-bit control signal, wherein m≥n. 2. The reading circuit of the image sensor according to claim 1, wherein the amplification displacement unit comprises: a programmable gain amplifier for amplifying the analog video signal to an amplified analog signal with a predetermined gain; and An adder/subtractor performs addition/subtraction operation on the amplified analog signal to output the amplified corrected analog signal. 3. The reading circuit of an image sensor as claimed in claim 1, wherein m≧k. 4. An analog/digital conversion method applied to an image sensor, which can sense images and output a line of analog image signals, characterized in that the method includes the following steps: (a). converting the row of analog video signals into a corresponding m-bit digital signal; and (b). Controlled by a k-bit control signal, the m-bit digital signal is converted into an m-bit digital signal for subsequent digital signal processing, wherein m≥n. 5. The analog/digital conversion method as claimed in claim 1, characterized in that: in the step (a), after generating the line of analog video signals, a step of amplifying and correcting the analog video signals is further included. 6. An image sensor, characterized in that it comprises: A sensing array, used for sensing images and sequentially outputting a row of analog image signals under control; and A readout circuit comprising: An amplification displacement unit, which is used to amplify and modify the line of analog image signals to output an enlarged and corrected analog signal; an m-bit analog/digital converter for converting the amplified corrected analog signal into a corresponding m-bit digital signal; and An m to n-bit digital conversion unit converts the m-bit digital signal into an n-bit digital signal for output according to a k-bit control signal, wherein m≥n. 7. The image sensor according to claim 6, characterized in that: the amplification displacement unit comprises: a programmable gain amplifier for amplifying the analog video signal to an amplified analog signal with a predetermined gain; and An adder/subtractor performs addition/subtraction operation on the amplified analog signal to output the amplified corrected analog signal. 8. The image sensor as claimed in claim 7, wherein m≧k.

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