KR100868650B1 - Apparatus for reducing Lens effect in image sensor - Google Patents

Abstract

The present invention relates to a CMOS image sensor, and more particularly, to an apparatus for compensating for lens effects occurring in an image sensor. The present invention provides a CMOS image sensor having a plurality of pixel arrays for providing data about an image, comprising: a control unit outputting an address of a corresponding pixel to be read to a gain adjusting unit according to an input control signal; A gain adjusting unit which receives an address of a pixel which is an output of the controller and outputs a gain value according to the address of the pixel; And a compensator configured to receive a gain value, which is an output of the gain adjuster, to compensate and output pixel data that is an output of the pixel array, wherein the gain adjuster comprises an externally adjustable gain table. Provided is a lens effect compensation device.

Image Sensor, Lens Effect, Gain Table, Micro Lens Shift

Description

Apparatus for reducing Lens effect in image sensor             

Figure 1a is a cross-sectional view showing a cross-sectional structure of the image sensor module built in the camera mounted on the mobile communication equipment,

1B is a plan view showing a lens effect on a pixel array of an image sensor;

2 is a block diagram showing the configuration of a lens effect compensator according to an embodiment of the present invention;

Figure 3 is a flow chart showing the operation sequence of the lens effect compensation apparatus according to an embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

21: control unit

22: gain adjustment unit

23: compensation

The present invention relates to a CMOS image sensor, and more particularly, to an apparatus for compensating lens effects in an image sensor used in mobile communication equipment.

In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal. Among them, a charge coupled device (CCD) includes individual metal-oxide-silicon (MOS) capacitors. A device in which charge carriers are stored and transported in a capacitor while being in close proximity, and a Complementary MOS image sensor uses CMOS technology that uses a control circuit and a signal processing circuit as peripheral circuits. A device employing a switching scheme that creates MOS transistors as many as pixels and sequentially detects output using them.

CCD (charge coupled device) has many disadvantages such as complicated driving method, high power consumption, high number of mask process steps, complicated process, and difficult to implement signal processing circuit in CCD chip. In order to overcome such drawbacks, the development of a CMOS image sensor using a sub-micron CMOS manufacturing technology has been studied in recent years. The CMOS image sensor forms an image by forming a photodiode and a MOS transistor in a unit pixel and sequentially detects signals in a switching method.As a CMOS manufacturing technology, the CMOS image sensor consumes less power and has 30 to 40 masks. Compared to CCD process that requires two masks, the process is very simple, and it is possible to make various signal processing circuits and one chip, which is attracting attention as the next generation image sensor.

With the recent development of mobile communication equipment, mobile communication equipment equipped with small cameras and the like is increasing rapidly. The camera mounted on the mobile communication equipment has an image sensor module built in, and the image sensor module has also been miniaturized in accordance with the trend of miniaturization of mobile communication equipment.

1A is a cross-sectional view illustrating a cross-sectional structure of an image sensor module embedded in a camera mounted on a mobile communication device, the image sensor package and an image sensor chip installed on a PCB board, glass for protecting the chip, A lens support and a lens are shown.

Such an image sensor module is actually used by being inserted into a product such as a camera, and since the mobile communication equipment and the image sensor module are both miniaturized, the lens mounted on the image sensor module is also miniaturized.

As the lens continues to be miniaturized in this manner, an undesirable phenomenon called a lens effect occurs. The lens effect is a phenomenon in which the focal length difference between the center portion and the peripheral portion of the pixel array in the image sensor is different due to the use of a lens that is too small.

In general, an image sensor chip can be roughly divided into a pixel array portion in which a plurality of pixels are two-dimensionally arranged and a signal processing portion in which a signal processing circuit is formed. The pixel array portion is a portion that generates image data from incident light. to be.

Therefore, if the brightness of the incident light is different in the central and peripheral portions of the pixel array, accurate image reproduction is impossible and image quality is deteriorated.

FIG. 1B illustrates a difference in brightness of light at a central portion defined as a circle inside and a peripheral portion defined as a circle outside in a pixel array including a plurality of pixels. In other words, the central part is the light area and the peripheral part is the light area.

In practice, when the image sensor is manufactured by applying a micro process having a fine line width of 0.35 μm, the above-described lens effect is further maximized. Therefore, the difference in brightness of light in the center and periphery of the pixel array is 50% or more. In the future, as the process technology develops and becomes finer, the lens effect is expected to intensify.

As a method for compensating for such a lens effect, a technique called microlens shift has been conventionally used. This technique properly processes the microlenses mounted per unit pixel in order to overcome the lens effect. In other words, the microlenses mounted on the pixels corresponding to the center portion of the pixel array and the microlenses mounted on the pixels corresponding to the peripheral portions of the pixel array are processed differently to reduce the lens effect.

However, since the role of the microlenses continues to decrease in the CMOS image sensor process of 0.35 µm or less, the microlens shift technique described above has no great effect.

An object of the present invention is to provide a lens effect compensator capable of reducing lens effects in a CMOS image sensor.

The present invention for achieving the above object, in the CMOS image sensor having a plurality of pixel array for providing data for the image, according to the input control signal to output the address of the pixel to be read to the gain adjuster Control unit; A gain adjusting unit which receives an address of a pixel which is an output of the controller and outputs a gain value according to the address of the pixel; And a compensator configured to receive a gain value, which is an output of the gain adjuster, to compensate and output pixel data that is an output of the pixel array, wherein the gain adjuster comprises an externally adjustable gain table. Provided is a lens effect compensation device.

The present invention reduces the lens effect by compensating pixel data by applying different gain values according to the central portion and the peripheral region of the pixel array using a gain table.

Hereinafter, the most preferred embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art can easily implement the technical idea of the present invention.

2 is a block diagram showing the configuration of a lens effect compensator according to an embodiment of the present invention will be described with reference to this.                     

The lens effect compensator according to an exemplary embodiment of the present invention receives a pixel data to be read and compensates the pixel data with an appropriate value and outputs the compensation unit 23 and a control signal to receive the address of the pixel to be read. The control unit 21 calculates a counter and outputs the pixel address to the gain adjusting unit 22, and receives a pixel address that is an output of the control unit 21, and selects a different gain value according to the input pixel address to compensate the unit 23. And a gain adjusting section 22 for outputting the signal.

Referring to Fig. 2, first, pixel data will be described. The pixel data is a signal having information of one frame in synchronization with the vertical synchronization signal and the horizontal synchronization signal as the output of the pixel array.

Next, the control unit 21 calculates the address of the pixel to be read using a counter according to the input control signal, and outputs it to the gain adjusting unit 22.

The gain adjusting unit 22 receives a pixel address. Different gain values are output to the compensator 23 by discriminating whether the pixel is located at the center of the pixel array or the pixel at the periphery of the pixel array according to the input pixel address. The gain adjusting unit 22 according to an embodiment of the present invention has the gain values for the center portion and the peripheral portion in the form of a table, and outputs different gain values to the compensation unit 23 according to the input pixel address.

For example, assuming that 1 is applied as a gain value to a pixel located at the center of the pixel array, and 2 is applied as a gain value to a pixel located at the periphery of the pixel array, the data of the pixels located at the center part is compensated. Since 1 is multiplied at 23, the original data is output as it is, and data of pixels located in the peripheral portion is multiplied by 2, so data having twice the brightness is output from the compensator 23.

In an embodiment of the present invention, the lens effect is compensated for using the digital gain value, but the lens effect may be compensated for using the analog gain value.

In addition, in one embodiment of the present invention, the compensator 23 is configured to function as a multiplier, but an adder or other circuits may be applied in addition to the multiplier. This can be used as a compensator by selecting an appropriate circuit in consideration of specific image sensor chip size, usage environment, and operating voltage.

Next, you need to define how far to define the center part and how far to define the peripheral part of the pixel array. You can define the center part to have a rectangular shape or the center part to have a circular shape.

If you want to define the center of the pixel array to have a rectangular shape, if you know only the address of the four pixels corresponding to each vertex of the rectangle, you can easily define the center of the pixel array. In this case, the inside of the rectangle is defined as the center portion of the pixel array and the outside of the rectangle is defined as the peripheral portion of the pixel array.

In order for the center of the pixel array to have a circular shape, it is necessary to know the addresses of the pixels located at the circumference, so a very complicated circuit is required when using a digital signal. However, by using a digital-to-analog converter to convert the pixel address of the circumference into an analog signal and using this value, a simple circuit can be used to define the circular center part. In this case, the inside of the circle is defined as the center portion of the pixel array and the outside of the circle is defined as the peripheral portion of the pixel array.                     

3 is a flowchart illustrating an operation procedure of the lens effect compensator according to an exemplary embodiment of the present invention. Referring to this, the operation of the lens effect compensator according to an exemplary embodiment of the present invention will be described.

First, an address of a pixel is received (301). Next, in the area detection step 302, different gain values are respectively output according to the address of the pixel. The gain value is input to the area detection step in the gain table (303).

If it is determined as the center portion in the area detection step, the process proceeds to selecting a gain value of 1 from the gain table (304). If it is determined to be a peripheral part, it proceeds to selecting a gain value of 2 from the gain table. (305).

If the shape of the center portion is defined as a rectangle, the operation of the area detection step will be described in detail as follows. Since the pixel array is composed of a plurality of pixels arranged in two dimensions, each unit pixel has an address (X, Y) corresponding to the horizontal axis and the vertical axis.

Therefore, in order to make the center portion of the pixel array have a rectangular shape, the center portion may be defined as a set of pixels in which the X-axis address and the Y-axis address of the pixel are each located below a predetermined distance from the center point of the pixel array. This is expressed as follows.

The X-axis address of the pixel-the X-axis address of the center point <a

Y-axis address of pixels-A set of pixels whose Y-axis address <b of the center point is defined as the center region.

Likewise,                     

X-axis address of pixels-X-axis address of center point> a or

Y-axis address of the pixel-The set of pixels with Y-axis address> b of the center point is defined as the perimeter.

In this way, when divided into the center portion and the peripheral portion according to the address of the pixel, the corresponding gain value is multiplied by the pixel data to perform a compensation operation (306).

In an embodiment of the present invention, the pixel array is simply divided into a center portion and a peripheral portion, and different gain values are applied to each portion. In addition to this method, the pixel array is further subdivided to apply a gain value corresponding to each portion. You may.

As described above, the present invention is not limited to the above-described embodiments and the accompanying drawings, and the present invention may be variously substituted, modified, and changed without departing from the spirit of the present invention. It will be apparent to those of ordinary skill in the art.

Applying the present invention has an effect that can be properly compensated for the lens effect even in an increasingly smaller image sensor.

Claims (7)

In a CMOS image sensor having a plurality of pixel arrays for providing data about the image, A controller for outputting an address of a corresponding pixel to be read to a gain adjusting unit according to an input control signal; A gain adjusting unit which receives an address of a pixel which is an output of the controller and outputs a gain value according to the address of the pixel; And A compensation unit configured to receive a gain value, which is an output of the gain adjustment unit, to compensate and output pixel data which is an output of the pixel array; The gain adjusting unit may be configured as an externally adjustable gain table. Lens effect compensation device of image sensor. The method of claim 1, The gain adjusting unit for outputting a gain value according to the address of the pixel The first gain value is output when the addresses of the pixels corresponding to the center portion of the plurality of pixel arrays are input, and the second gain value is output when the addresses of the pixels corresponding to the peripheral portion of the plurality of pixel arrays are input. Lens effect compensation device of the image sensor, characterized in that. The method of claim 2, The center portion of the plurality of pixel array is a lens effect compensation device of the image sensor, characterized in that it is defined to have a rectangular or circular shape. The method of claim 2, And the first gain value is greater than the second gain value. delete The method according to claim 1 or 2, And the gain adjusting unit and the compensating unit use a digital signal. The method according to claim 1 or 2, And the gain adjusting unit and the compensating unit use an analog signal.

Images