JP2763292B2 - Image sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor for reading an image. [Prior art] Conventionally, image sensors used for image reading include a silicon crystal type such as a CCD and a bipolar type, and a thin film type such as a Cds and amorphous silicon. There is a type. On the other hand, the configuration of the color image reading apparatus includes, as color separation systems, a system in which a light source or a color filter is switched using a single image sensor and a simultaneous reading color separation system in which switching is not performed. The simultaneous reading color separation method includes a method in which a stripe filter is formed on a one-line image sensor to read out color separation signals in a time-sequential manner in a point-sequential manner, or a method in which a plurality of image sensors are provided in parallel for each separation color and line-sequential. There is a reading method. From the required performance of the image reading apparatus, a thin film type with a high reading speed is suitable as a high-speed type, and a unit-size type that can provide a wide light receiving area for the same reading resolution is suitable as a high sensitivity type. Here, in the case of a color image reading apparatus, a high sensitivity type is required particularly due to a decrease in the amount of incident light due to a color separation filter and a spectral sensitivity characteristic of the image sensor itself. In order to realize high-speed reading using a light source within a practical range. It is suitable that a stripe filter is configured in a 1 × silicon crystal type. However, in the case of the silicon crystal type, it is difficult to make a long type that covers 297 mm of the A4 longitudinal width with one chip due to manufacturing restrictions, and multiple lines are configured as one line sensor by devising physical arrangement. Things have recently emerged for high-speed reading. [Problems to be Solved by the Invention] In addition, a system in which a plurality of image sensors are provided in parallel for each separation color, and a line-sequential reading method is also configured with a silicon crystal type stripe filter, and color separation signals are time-divisionally point-sequentially. Even in the reading method, there is no light source having a flat spectral energy distribution in the wavelength range in which the amount of incident light is reduced due to the color separation filters, and in particular, the light transmittance is unbalanced for each color separation filter. For example, in the case of a combination of a color CCD having the spectral sensitivity distribution shown in FIG. 4 and a halogen lamp having a spectral distribution characteristic shown in FIG. 5, a total spectral distribution shown in FIG. As can be seen from the sensitivity characteristics, the output ratio of each filter is extremely different. When signal processing as shown in FIG. 7 is performed using this output value, S /
The N ratio becomes largely different, and finally performing color correction processing such as masking is a major factor that leads to deterioration of image quality. In FIG. 7, 100 is B having a blue (B) filter.
A three-line full-color line sensor in which a CCD 101, a G-CCD 102 having a green (G) filter, and an R-CCD 103 having a red (R) filter are formed on the same wafer;
Reference numeral 2703 denotes a signal processing unit for amplifying an output signal from each CCD to a voltage level corresponding to the reference level of the A / D converters 704, 705 and 706. Note that the signal processing units 702 and 703 are
Detailed illustration is omitted because it has the same configuration as 01. Therefore, in order to compensate for this, a special light source, for example, a blue-white (B
W) By using fluorescent tubes, 1: 1: 1 as shown in FIG.
However, it is necessary to newly design the spectral distribution characteristics of the light source according to the sensor, which leads to complicated design and cost increase. FIG. 10 shows the spectral distribution characteristics of the blue-white (BW) fluorescent tube. In FIG. 7, 701a is a first amplifier, and 701b is a second amplifier.
701c is used to sample and hold the output level of the dark output signal section where the light receiving section of the output signal from the CCD shown in FIG. The S / H circuit 701d is a comparator circuit for comparing the S / H dark output signal level with the reference level, and maintains the reference level of each CCD output signal amplified by the 701b, 701c, and 701d constant. And the first and second amplifiers 701a and 701b have an A / D converter.
Amplify each CCD output signal up to the converter dynamic range. By the way, B, G, R, the output signal ratio of each CCD 101, 102, 103 is different, for example, each output value 200mV, 400mV, 600mV
And the A / D converters 704, 705, 706 have 2V
Then, the total amplification factor in the signal processing unit for each color is B: 2V / 200mV
= 10, G: 2V / 400mV = 5, R: 2V / 600mV ≒ 3.3, and since the noise level output from each CCD is constant, the noise level of B and G for the R signal is B: 10 / 3.3 ≒ 3, G: 10/5 = 2
And the S / N ratio is relatively deteriorated. [Means for Solving the Problems] The present invention has been made to solve the above problems, and has a first line sensor and a second line having higher sensitivity than the first line sensor. A sensor and the first
The signal gain output from the second line sensor is set so that the signal level of the image signal output from the second line sensor and the signal level of the image signal output from the second line sensor are substantially the same. Level adjusting means for relatively lowering the level, and the first and second line sensors and the level adjusting means are provided on the same wafer. Embodiments Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is an example of a schematic internal configuration of an image reading element comprising a plurality of line sensors having different color filters according to the present invention. 101, 102 and 103 are silicon silicon photodiodes (P
D) Blue (B), Green (G), Red (R) on top
Are directly formed with a stripe filter made of an organic dye, and 104a, 104b, 105a, 105b, 106a, and 106b are B
A CCD shift register for transferring the charges stored in the light receiving units 101, G light receiving unit 102, and R light receiving unit 103 to the output unit. The CCD shift register separates the charge for each pixel from the light receiving units 101, 102, 103 into right and left pixels. It is composed of two CCD registers, a and b, for transferring data. 107a, 107b, 108a, 108b, 109a, 1
09b is a light receiving unit 101, 102, 1 that is separated and transferred to the left and right
This is a floating diffusion amplifier (FDA) composed of an output capacitance section called a floating diffusion (FD) that detects charges from 03 and converts it into a voltage, and an amplifier that receives and outputs the output capacitance section. In addition, the light receiving unit 101 and the CCD shift registers 104a, 104b, FDA1
B-CCD sensor composed of 07a and 107b, G-CCD sensor composed of light receiving section 102 and CCD shift registers 105a and 105b, and FDAs 108a and 108b, light receiving section 103 and CCD shift registers 106a, 106b and FDA109.
The R-CCD sensor consisting of a and 109b is formed on the same silicon Si wafer, and each CCD sensor can be driven separately. FIG. 2 is a diagram describing the B-CCD in FIG. 1 in detail, and will be described according to the operation. The light receiving unit 101 includes a photoelectric conversion unit 101a and storage units 201a and 201b, and the electric charge stored in the light receiving unit 101 is a shift gate pulse φ applied to the shift gates 202a and 202b.
_The data is transferred to the CCD shift registers 104a and 104b by the _SG . At this time, the charge stored in the even-numbered pixels is
The charges stored in the D shift register 104b and the odd pixels are transferred to the odd CCD shift registers 104a. CCD shift register 104a in which the period of the shift gate pulse phi _SG corresponding to the accumulation time, 104b transfers output unit FDA107a, in 107b charges have been sent from the light receiving unit 101 2-phase clock phi _1, according phi _2. The FDAs 107a and 107b are composed of output gates (OD) 203a and 203b, output capacitors 204a and 204b, and amplifiers 205a and 205b. The FDAs 107a and 107b transfer electric charges sent by the CCD shift registers 104a and 104b to the capacitors 204a and 204b. The charge transferred over the output gates 203a and 304b is converted into a voltage corresponding to the charge amount by the output capacitance units 204a and 204b, and the charge is transferred to the two stages of the amplifier units 205a and 205b. The impedance is converted by the source follower amplifier and output. Here, the FDAs 107a and 107b will be described in more detail with reference to FIG. Here, the amplifier unit 205 is replaced with a one-stage source follow amplifier for simplification. 301 and 302 is a clock electrode of each phi ₁ and phi ₂ of 3
02 is an electrode of the output gate 203, and the operation is as described above. A reset electrode 303 resets the output capacitance section (FD) 204 to the voltage V _DD of the reset drain 304 by periodically applying a pulse to the reset electrode 303. The output capacitor (FD) 204 is separated from the reset drain RD by the reset 303 until the signal charge is injected into the output capacitor (FD) 204. Now, let Qs be the amount of signal charge sent to the output capacitor (FD) 204, C _{FD be} the capacitance of the output capacitor (FD) 204, Ar be the voltage gain of the source follower amplifier, and be the transfer conductance of the amplified M ⁰ SFET. gm, the output signal ΔV is And is proportional to the signal charge Qs. Output capacity (FD)
It can be seen that the smaller the capacity of 204, the higher the output voltage. Therefore, the capacity C _FD of the output capacity section (FD) 204 is changed to B-CC
By increasing the B-CCD, G-CCD, and R-CCD in order in inverse proportion to the sensitivities of the light-receiving sections 101, 102, and 103 of the D, G-CCD, and R-CCD, the amplification factor of the output section is reduced, and the overall B −CCD, G−C
The output voltage ratio of CD, R-CCD is set to be approximately 1: 1: 1. Here, as a light source for determining this ratio, for example, a light source using an A light source which is a general photometric light source and a light source using an infrared cut filter to prevent the influence of the sensitivity on the long wavelength side of the CCD is used. Determine the output voltage ratio described above. Further, the control of the capacitance _CFD of the output capacitance unit (FD) 204 is possible by changing the pattern area of the output capacitance unit (FD) 204. That is, the output capacitance _CFD decreases as the pattern area decreases, and increases as the pattern area increases. Therefore, in this embodiment, B-CCD, G-CCD, R-CCD
The above-described output ratio is achieved by increasing the pattern area of the output capacitance section (FD) 204 in the order of in inverse proportion to the sensitivity. FIG. 11 shows another embodiment. In the above embodiment, the capacitance C _FD of the output capacitance section (FD) of the FDA section is adjusted in inverse proportion to the sensitivity of the light receiving sections 101, 102, and 103, and B-CCD, G is output as the CCD output value of each color.
The output ratio of -CCD, R-CCD was set to 1: 1: 1. Therefore, the pattern area of the output capacitance section (FD) of the FDA section is set to R
−CCD, G-CCD, B-CCD in this order, but in the embodiment of FIG. 11, the output capacitance section (F
The value of the capacity C _FD of D) is for each color CCD, B-CCD, G-CCD, R-CCD
FDA parts 107a, 107b, 108a, 108b,
Attenuator sections 1101a, 1101b, 1102 on the output side of 109a, 109b
By configuring a, 1102b, 1103a, and 1104b, the output ratio of each color CCD is made approximately 1: 1: 1. For example, B-CCD, G-CCD, R-CCD
Are 200 mV, 400 mV, and 600 mV, the attenuator ratio of each of the attenuator sections 1101a, 1101b, 1102a, 1102b, 1103a, and 1103b is 1 (the attenuator sections 1101a and 1101b are not attenuated), and the attenuator sections 1102a and 1102b are The attenuator is configured to be 0.5 and 0.33 in the attenuator sections 1103a and 1103b. By doing so, the same effect as in the above-described embodiment can be obtained. As described above, in a color image pickup device having a plurality of CCDs in parallel for each separation color and reading out line-sequentially, the amplification degree of the output amplification unit of the output unit of each color CCD is independently varied for each separation color, By making the CCD output signal levels equal for each separation color, it is possible to prevent imbalance in the output signal level for each separation color that occurs in the conventional case, and to equalize the signal state for each separation color. It is possible. Further, since the output signal levels of the respective separated colors are equal, the processing circuit for the output signals can be made the same for all the colors, thereby preventing cost increase. [Effect] As described above, according to the present invention, the first line sensor, the second line sensor having higher sensitivity than the first line sensor, and the output from the first line sensor are provided. Level adjustment for relatively lowering the signal gain output from the second line sensor so that the signal level of the image signal and the signal level of the image signal output from the second line sensor are substantially the same. Means,
The first and second line sensors and the level adjusting means are provided on the same wafer. And, with such a configuration, the relative sensitivity due to the difference in the sensitivity of the line sensors provided on the same wafer is determined.
S / N variation can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of an image reading device according to the present invention, FIG. 2 is an internal configuration diagram of the image reading device, FIG. 3 is a configuration diagram of an output unit,
FIG. 4 is a diagram showing a spectral sensitivity distribution of a conventional color CCD, FIG. 5 is a diagram showing a spectral distribution characteristic of a halogen lamp, FIGS. 6 and 9 are diagrams showing an overall distribution sensitivity characteristic, and FIG. FIG. 8 is a diagram showing the output timing of each signal, FIG. 10 is a diagram showing the spectral distribution characteristics of the fluorescent tube, FIG.
The figure shows the configuration of another embodiment, where 100 is a 3-line full-color line sensor, 101, 102, and 103 are light-receiving units, 107a and 10
7b, 108a, 108b, 109a and 109b are floating diffusing amplifiers.

Claims (1)

(57) [Claims] A first line sensor, a second line sensor having a higher sensitivity than the first line sensor, a signal level of an image signal output from the first line sensor, and an output from the second line sensor Level adjusting means for relatively lowering the signal gain output from the second line sensor so that the signal level of the image signal to be output becomes substantially the same as the first and second lines. An image sensor, wherein the sensor and the level adjusting means are provided on the same wafer. 2. 2. The image sensor according to claim 1, wherein said first line sensor and said second line sensor output image signals of different colors, respectively. 3. The image pickup device according to claim 1 or 2, wherein the level adjusting unit is configured to control the first level by the first level.
Amplifying the image signal output from the line sensor
An image pickup device comprising: amplifying means of (1) and a second amplifying means for amplifying an image signal output from the second line sensor.