Gamma correction circuit for analog gamma-correction of CMOS image sensor

专利摘要:
PURPOSE: A gamma correction circuit for analog gamma correction in a CMOS(Complementary Metal Oxide Semiconductor) image sensor is provided to perform gamma correction in analog, so as to reduce quantization noise and simply implement a circuit for the analog gamma correction. CONSTITUTION: In a gamma correction circuit that performs analog gamma correction for data outputted from each pixel of a CMOS image sensor, a nonlinear lamp voltage generation unit generates a nonlinear lamp voltage by having a DAC(Digital-to-Analog Converter,100) and a first integrator(120) and a second integrator(140). The DAC receives a gain value of a digital code from an external control block, for conversion into an analog voltage. The first and second integrators configured in switch capacitor structures integrate the converted analog voltage twice consecutively. And an output of the DAC is a gain factor of the nonlinear lamp voltage generation unit.
公开号:KR20020058490A
申请号:KR1020000086597
申请日:2000-12-30
公开日:2002-07-12
发明作者:최수창
申请人:박종섭；주식회사 하이닉스반도체；
IPC主号:

专利说明:

Gamma correction circuit for analog gamma-correction of CMOS image sensor
[10] The present invention relates to an image sensor, and more particularly to a gamma correction circuit for analog gamma correction in a CMOS image sensor.
[11] In general, an image sensor refers to a device that captures an image by using a property of a semiconductor that reacts to light. Each part of each subject in the natural world has different electrical values at each pixel of the device because the brightness and wavelength of light are different from each other. Is what it does. To do this, an image sensor is a pixel array consisting of tens of thousands to hundreds of thousands of pixels, a device that converts the analog voltage detected by hundreds of pixels into a digital voltage, and hundreds to thousands of storage. Device and the like.
[12] The image sensor configured as described above performs digital gamma correction as shown in FIG. 1 by using digital operation to improve image quality of the output image. However, when gamma correction is performed digitally, a large number of missing codes are generated in the gamma-corrected output data, but rather, the image quality is degraded due to quantization noise due to the missing code.
[13] Meanwhile, in order to solve such a problem, gamma correction may be performed in an analog manner as illustrated in FIG. 2.
[14] FIG. 2 is a graph illustrating digital image codes obtained by performing analog gamma correction on analog raw image data and converting them digitally through an analog-to-digital converter. .
[15] As shown in FIG. 2, analog image data values corresponding to each code from digital image code 0 to 9 converted to digital after gamma correction of the analog exist, thereby eliminating the missing digital code, thereby reducing the expressiveness of the image sensor. It can be used, which ensures high image quality of the image sensor. That is, analog gamma correction has an advantage of minimizing quantization noise compared to digital gamma correction.
[16] As such, it is necessary to perform analog gamma correction in the image sensor for better image quality. However, the conventional analog gamma correction circuit is very complicated and thus difficult to implement. Therefore, there is a need for an apparatus capable of performing analog gamma correction in an image sensor with only a simple analog circuit.
[17] On the other hand, the conventional analog gamma correction circuit is provided with a linear ramp voltage generation device to perform analog-to-digital conversion, the operating principle of the related art CMOS image sensor is conceptually shown in FIG.
[18] Referring to FIG. 3, in the conventional CMOS image sensor, an analog pixel value of the Vpixel axis is compared with an output signal of a linear ramp voltage generator and output as a digital code in a range of 0 to 255.
[19] As such, in a circuit for performing analog gamma correction using a linear ramp voltage generator, another problem may occur in that the resolution of the converted digital code is degraded due to the characteristics of the linear ramp voltage.
[20] SUMMARY OF THE INVENTION An object of the present invention is to provide an analog gamma correction circuit for analog gamma correction in an image sensor having a simpler structure while improving image quality.
[1] 1 is a graph for conceptually explaining digital gamma correction.
[2] FIG. 2 is a graph illustrating digital image codes obtained by performing analog gamma correction on analog raw image data and converting them digitally through an analog-digital converter. FIG.
[3] 3 is a view for conceptually explaining the operating principle of the CMOS image sensor according to the prior art.
[4] 4 is a view for conceptually explaining the operating principle of the CMOS image sensor through the non-linear lamp voltage of the non-linear lamp voltage generation device according to an embodiment of the present invention.
[5] 5 is a circuit diagram of a non-linear lamp voltage generation device according to an embodiment of the present invention.
[6] * Description of the main parts of the drawing
[7] 100: DAC
[8] 120, 140: Integrator
[9] C0, C6: feedback capacitor
[21] In order to achieve the above object, the present invention provides a gamma correction circuit for performing analog gamma correction on data output from each pixel of a CMOS image sensor. Digital-to-analog conversion means for converting; And nonlinear lamp voltage generating means having first and second integrating means of a switch capacitor structure for continuously integrating the analog voltage converted in the digital-analog converting means twice in succession.
[22] DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. do.
[23] Analog gamma correction circuit of the present invention is a simple second integrator (2 ^nd order integrator) and also having a device for generating a linear ramp voltage as shown in Figure 5 using.
[24] By generating the nonlinear lamp voltage as shown in FIG. 4 in the nonlinear lamp voltage generating device of the present invention, when the 90 degree rotation region of the drawing is rotated 90 degrees counterclockwise, the analog pixel value is converted into a digital code value. When gamma corrected, it can be seen that the analog-to-digital conversion is performed. Here, the 90 degree rotation mathematically means the inverse function to make the inverse of the gamma transfer function (gamma transfer function) to the ramp voltage generator.
[25] Meanwhile, the gamma transfer function is expressed by Equation 1 below.
[26] gamma (x) = x ^0.45
[27] Accordingly, the inverse function of the function of Equation 1 becomes a ramp voltage signal and is expressed as Equation 2 below.
[28] ramp (x) = gamma ^-1 (x) = x ^2.222
[29] In addition, since the ramp voltage signal proposed by the present invention is a signal output from the secondary integrator, that is, a signal expressed by an integral of a constant twice, a quadratic functional formula as shown in Equation 3 below becomes an output signal.
[30]
[31] Equation 3 is slightly different from Equation 2, but may be used for the actual gamma correction. Here, when a is '2', the ramp voltage signal is expressed by Equation 4 below.
[32] ramp (x) = x ² ≒ gamma ^-1 (x)
[33] 5 is a circuit diagram of a non-linear lamp voltage generation device according to an embodiment of the present invention.
[34] As shown in FIG. 5, the non-linear lamp voltage generation device of the present invention receives a gain value (gain_select) from an external control block as a digital code and converts it into an analog voltage. The digital-to-analog converter (DAC) 100 and the DAC ( The first and second integrators 120 and 140 of the switch capacitor structure are integrated to integrate the analog voltage converted in step 100 but continuously perform second integration. Here, since the internal circuits of the integrators 120 and 140 of the DAC 100 and the switch capacitor structure have a configuration well known in the art, a detailed description thereof will be omitted.
[35] When the digital code is input to the DAC 100 in the nonlinear lamp voltage generator of the present invention configured as described above, the DAC 100 converts the input digital code into an analog voltage a, and the converted analog voltage a is a switch capacitor. It is input to the first integrator 120 of the structure and integrated first. The output of the integrated first integrator 120 is ax. The first integrated signal is again integrated by the second integrator 140, where the value of the feedback capacitor C6 is half the value of the feedback capacitor C0 provided in the first integrator 120. The gain is doubled so that the final output of the second integrator 140 is ax ² . In this case, the output a of the DAC 100 becomes a gain factor of the ramp voltage generator, and the DAC 100 receives a gain value as a digital code from an external control block. Here, the gain factor is used for color correction.
[36] Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.
[37] According to the present invention, the quantization noise can be reduced by performing gamma correction in analog, and the circuit for analog gamma correction can be more easily implemented.

权利要求:
Claims (4)
[1" claim-type="Currently amended] A gamma correction circuit for performing analog gamma correction on data output from each pixel of a CMOS image sensor,
Digital-to-analog conversion means for receiving a gain value of a digital code from an external control block and converting it into an analog voltage;
Nonlinear lamp voltage generating means having first and second integrating means of a switch capacitor structure for continuously integrating the analog voltage converted by the digital-analog converting means twice in succession;
Analog gamma correction circuit comprising a.
[2" claim-type="Currently amended] The method of claim 1, wherein the output of the digital-to-analog conversion means is:
And a gain coefficient of the nonlinear lamp voltage generating means.
[3" claim-type="Currently amended] The method of claim 1, wherein the second integration means,
And a double gain of said first integrating means.
[4" claim-type="Currently amended] The method of claim 3, wherein the feedback capacitance of the first integration means,
And an amplitude of twice the feedback capacitance of said second integrating means.

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同族专利:

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公开号 | 公开日

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KR100384872B1|2003-05-22|

引用文献:

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公开号 | 申请日 | 公开日 | 申请人 | 专利标题

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法律状态:
2000-12-30|Application filed by 박종섭, 주식회사 하이닉스반도체

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2000-12-30|Priority to KR10-2000-0086597A

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2002-07-12|Publication of KR20020058490A

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2003-05-22|Application granted

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2003-05-22|Publication of KR100384872B1

优先权:

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申请号 | 申请日 | 专利标题

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KR10-2000-0086597A|KR100384872B1|2000-12-30|2000-12-30|Gamma correction circuit for analog gamma-correction of CMOS image sensor|