JP2016111445A - Photographing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively suppress the generation of noise due to a current source transistor while suppressing an increase in current consumption. A current variable unit that can change a current for each column is provided, and a current setting by the current variable unit is changed according to a noise amount for each column. [Selection] Figure 4

Description

  The present invention relates to an imaging apparatus using an imaging element.

  In recent years, CMOS type solid-state imaging devices have been widely used in imaging devices such as digital still cameras and digital video cameras. The pixel portion of the CMOS image sensor includes a photodiode, a transfer transistor, a floating diffusion, a reset transistor, an amplification transistor, and a selection transistor. In addition, a vertical output line and a current source transistor connected to the vertical output line are provided, and the amplification transistor and the current source transistor of the pixel portion form a source follower via the vertical output line, and the potential on the vertical output line is external (Patent Document 1).

If a trap order exists in the gate insulating film of the current source transistor, 1 / f noise in which the noise power spectrum is proportional to the reciprocal of the frequency f may occur. In the imaging apparatus configured as in Patent Document 1, when 1 / f noise occurs in the current source transistor, fluctuation occurs in the current flowing through the vertical output line. As a result, noise is generated in the output signal of the amplification transistor in the pixel portion. The amount of such noise is likely to be different for each vertical output line due to manufacturing effects, and if there is a portion of the vertical output line with a large amount of noise, it may be noticeable as linear noise. . Further, the noise amount of 1 / f noise is expressed by the following equation.
v ² = K / (LWI)
v: Noise amount L: Transistor gate length W: Transistor gate width I: Current

  Therefore, it is possible to reduce 1 / f noise by increasing the current of the vertical output line.

JP 2003-51989

  However, when the current of the vertical output line is increased, the power consumption of the entire sensor is increased and the battery is consumed quickly, or the image quality is deteriorated due to an increase in dark current due to heat generation.

  An object of the present invention is to provide an imaging device capable of effectively suppressing the occurrence of linear noise due to 1 / f noise of a current source transistor and suppressing the increase in power consumption and obtaining a good image quality. It is to be.

  An imaging apparatus according to the present invention includes a plurality of pixels arranged in a matrix, a column output line that is provided for each column and outputs a pixel signal from the plurality of pixels, and a current source that supplies a current to the column output line An image sensor including: a detection unit that detects a noise amount of the column output line for each column; and a current supplied from the current source is changed for each column according to the noise amount detected by the detection unit. And a control means for controlling as described above.

  According to the present invention, it is possible to provide an imaging apparatus capable of obtaining high image quality while suppressing an increase in power consumption.

1 is an overall block diagram of an imaging apparatus in an embodiment. 1 is an overall configuration diagram of an image sensor in an embodiment. FIG. The circuit diagram of the unit pixel in an Example. The detailed explanatory view of the current source circuit in an example. The figure which shows the noise amount in-plane dispersion | variation for every perpendicular | vertical output line in an Example. The figure which shows the noise amount in-plane dispersion | variation for every perpendicular | vertical output line in an Example.

  Hereinafter, an embodiment of the present invention will be described. FIG. 1 is an overall block diagram of an imaging apparatus according to an embodiment of the present invention.

  The taking lens 1110 forms an optical image of a subject on the image sensor 1101, and zoom control, focus control, aperture control, and the like are performed by a lens driving circuit 1109. The image sensor 1101 captures the subject imaged by the photographing lens 1110 as an image signal. Details of the image sensor 1101 will be described later. The timing generation circuit 1102 outputs a drive timing signal to the image sensor 1101.

  The signal processing circuit 1103 performs analog-digital conversion processing and various correction processes on the image signal output from the image sensor 1101. The overall control / arithmetic circuit 1104 controls various calculations and the entire imaging apparatus. The overall control / arithmetic circuit 1104 includes a white balance adjustment unit (not shown), and adjusts the white balance by multiplying each color pixel signal of the captured image by the white balance.

  The memory 1105 temporarily stores image data. A display circuit 1106 displays various information and captured images. A detachable recording circuit 1107 such as a semiconductor memory records or reads image data. The operation circuit 1108 electrically accepts an operation by a user of an operation member of the digital camera.

  FIG. 2 is a diagram illustrating the overall configuration of the image sensor 1101. The image sensor 1101 includes a pixel region 1, a vertical scanning circuit 2, a current source circuit 3, a readout circuit 4, a horizontal scanning circuit 5, and an output amplifier 6.

  In the pixel region 1, unit pixels 100 are arranged in a matrix. Here, in order to simplify the description, a 4 × 4 16-pixel array is shown, but a larger number of pixels are arranged in practice. Each unit pixel 100 is provided with color filters of a plurality of types of colors.

  The vertical scanning circuit 2 selects the pixels in the pixel area 1 in units of one row, and sends a drive signal to the pixels in the selected row.

  The current source circuit 3 is provided in each column and forms a source follower in combination with the unit pixel 100. The readout circuit 4 is provided in each column, amplifies the output signal of the source follower composed of the unit pixel 100 and the current source circuit 3, and samples and holds the output signal.

  The horizontal scanning circuit 5 sends out a signal for sequentially outputting the signal sampled and held by the column readout circuit 4 to the output amplifier 6 for each column. The output amplifier 6 outputs the signal output from the column readout circuit to the outside by the operation of the horizontal scanning circuit.

  FIG. 3 is a circuit diagram of the unit pixel 100. As shown in FIG. 3, the unit pixel 100 includes a photodiode 101, a transfer switch 102, a floating diffusion 103, a reset switch 104, an amplification transistor 105, and a selection switch 106.

  The photodiode 101 as a photoelectric conversion element functions as a photoelectric conversion unit that receives light incident on the pixel 101 and generates a signal charge corresponding to the amount of received light. The transfer switch 102 is driven by the transfer pulse signal PTX and transfers the signal charge generated by the photodiode 101 to the floating diffusion 103.

  The floating diffusion 103 functions as a charge-voltage converter that temporarily holds the charge transferred from the photodiode 101 and converts the held charge into a voltage signal. The amplification transistor 105 is a source follower MOS transistor, amplifies a voltage signal based on the charge held in the floating diffusion 103, and outputs it as a pixel signal.

  The reset switch 104 is driven by a reset pulse signal PRES, and resets the potential of the floating diffusion 103 to the reference potential VDD. The selection switch 106 is driven by the vertical selection pulse signal PSEL, and outputs the pixel signal amplified by the amplification transistor 105 to the vertical output line (column output line) 107.

  Next, details of the current source circuit 3 will be described with reference to FIG. First, a reference current circuit 201 serving as a constant current source serving as a reference for all the columns supplies reference currents of current variable circuits R1 to R4 described later. The reference current circuit 201 is generally composed of a MOS transistor installed on the vertical output line, a resistor for determining a supply current value, and the like, but detailed description thereof is omitted here.

  In addition, a plurality of vertical output lines 107-1 to 107-n (in this embodiment, there are four columns, 107-4) connected in common to the pixels in each column of a two-dimensional matrix are provided for each column. The variable current circuits R1 to R4 for changing the current value supplied to the are connected.

  The current variable circuits R1 to R4 set a current value supplied to each column of the vertical output lines 107-1 to 107-4 with respect to the reference current supplied from the reference current circuit 201. The current setting values of the current variable circuits R1 to R4 are controlled for each column by a control signal from the control logic circuit 202 serving as control means.

  The constant current amount for each column may be changed in a plurality of stages by selectively switching, for example, a plurality of transistors having different sizes in the current variable circuits R1 to R4. Not a thing.

  For the control logic circuit 202, for example, it is possible to change the internal settings of the current variable circuits R1 to R4 by a known control such as sending a setting of several bits to each column by serial communication. Good.

  FIG. 5 is an example graph showing in-plane variation in noise amount for each vertical output line. Here, data for thousands of columns used in a general digital camera or the like is shown. In FIG. 5, in order to detect the noise amount for each column, the variation σ of the output signal in the dark of the image sensor is calculated for each column, and the ratio σ / σave with the average value σave of the calculated σ for each column is calculated. It is what I have sought.

  FIG. 5A shows a state in which the current of the first current value is set to be supplied to the vertical output lines of all columns as the supply current value of the vertical output lines. When the noise amount is detected for each column by the noise detection means, a column having a large σ / σave is detected as shown in FIG. In this state, the vertical output line (column output line) of the column in which the detected noise amount is larger than the first threshold (noise determination threshold 1) is stored, and the first current value is stored in the stored vertical output line. The control logic circuit 5 performs control so as to supply a second current value larger than that. By such control, as shown in FIG. 5B, it is possible to suppress the amount of noise in a column having a large σ / σave.

  For detection of a column with a large amount of noise, for example, the difference between the maximum value Max and the minimum value Min of each pixel may be obtained from a plurality of image data at the time of manufacture, or a dark image is acquired when the camera is activated. A method of performing detection and storage before the actual photographing may be used.

  In the embodiment described above, the amount of noise in a column with a large amount of noise is suppressed by setting the constant current amount of the detected vertical output line in the column with a large amount of noise to a second amount of current that is larger than the first current value. This can increase power consumption. Therefore, a column in which the constant current amount may be decreased may be detected to suppress an increase in current consumption.

  FIG. 6 is a graph showing the in-plane variation of the noise amount for each vertical output line, as in FIG. In order to detect the noise amount for each column, the variation σ of the output signal in the dark of the image sensor is calculated for each column, and the ratio σ / σave with the average value σave of the calculated σ for each column is obtained. is there. FIG. 6 shows a state in which a current having a third current value smaller than the first current value is supplied to the vertical output lines of all columns as the supply current value of the vertical output lines. ing. That is, a situation is set in which σ / σave increases by driving to supply a small current value.

  In this situation, the vertical output line (column output line) of the column that falls below the second threshold value (noise determination threshold value 2) that is smaller than the first threshold value is stored. Then, the control logic circuit 5 controls to supply a third current value smaller than the first current value to the vertical output line of the stored column.

  By controlling in this way, the first current value is supplied to the vertical output line of the normal noise amount column. Further, the second current value is supplied to the vertical output line of the column in which the detected noise amount exceeds the noise determination threshold value 1. Further, the control is performed so that the third current value is supplied to the vertical output line of the column in which the detected noise amount is lower than the noise determination threshold 2, thereby suppressing the increase in the total current consumption and the noise. It is possible to reduce noise in a large amount of columns.

1 pixel region 2 vertical scanning circuit 3 current source circuit 4 readout circuit 5 horizontal scanning circuit 6 output amplifier 100 unit pixel 101 photodiode 102 transfer switch 103 floating diffusion 104 reset switch 105 amplification transistor 106 selection switch 107-1 to 107-4 vertical Output line 201 Reference current circuit 202 Control logic circuit R1-R4 Current variable circuit

Claims (4)

An imaging device comprising: a plurality of pixels arranged in a matrix; a column output line that is provided for each column and outputs a pixel signal from the plurality of pixels; and a current source that supplies a current to the column output line; ,
Detecting means for detecting the noise amount of the column output line for each column;
Control means for controlling the current supplied by the current source to change for each column according to the amount of noise detected by the detection means;
An imaging apparatus comprising:   The control means supplies a current having a first current value to a column output line of a column in which the amount of noise detected by the detection means is smaller than the first threshold and larger than the second threshold, and the detection means The current source is controlled so that a current having a second current value larger than the first current value is supplied to a column output line of a column having a detected noise amount larger than the first threshold value. The imaging apparatus according to claim 1.   The control means supplies a current having a first current value to a column output line of a column in which the amount of noise detected by the detection means is smaller than the first threshold and larger than the second threshold, and the detection means The current source is controlled so that a current having a third current value smaller than the first current value is supplied to a column output line of a column whose detected noise amount is smaller than the second threshold value. The imaging apparatus according to claim 1 or 2.   The control means controls the current of the first current value to be supplied to the column output lines of all the columns when the detection unit detects a column whose noise amount is larger than the first threshold value. When detecting a column having a noise amount smaller than the second threshold by the detecting means, control is performed so that a current having a third current value is supplied to the column output lines of all columns. The imaging apparatus according to any one of claims 1 to 3, wherein the imaging apparatus is characterized.

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