JPS5847223A - Method and device for correcting sensitivity of solid state sensor - Google Patents

Abstract

PURPOSE:To perform high accuracy correction by knowing beforehand the sensitivity characteristics of a referent photo element and other photo elements to the light exposure and correcting the output of each photo element when the amount of light of an object to be measured is measured. CONSTITUTION:Six CCD sensors 100 are arranged in parallel, and their outputs are inputted to a data RAM104 through a multiplexer 101, sample and hold circuit 102 and A/D converter 103. The output of the RAM104 is outputted to a calculator 113 through an addition and subtraction device 110, multiplier 111 and an input port 112. The output of the calculator 113 is connected to the RAM104, constant number RAM's 106 and 108. Gates G1-G14 are controlled by a means such as computer, and specified calculation is carried out for the photo element of the sensor 100 with respect to a reference photo element that is set up arbitrarily. The scatter in the sensitivities among the photo elements is thereby corrected and high accuracy optical measurement can be made.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for completely correcting the sensitivity between each photoelement in a solid-state sensor in which a plurality of photoelements such as photodiodes or phototransistors are arranged in parallel.

2. Description of the Related Art In optical measuring devices such as MTF (modulation transfer function) testers that test lens aberrations, etc., solid-state sensors such as COD (charge coupled device) sensors are used to measure light intensity distribution. The CCD sensor is, for example, 2048
(2048 bits) photoelements with a center distance of 1
They are arranged in parallel with a width of 3 μm, and can be used to transmit the output corresponding to the exposure amount of each photoelement to a signal processing device and measure exposure distribution, etc. On the other hand, each photoelement of a CCD sensor has variations in its sensitivity due to variations in manufacturing parameters during the manufacturing process ('C) and properties of the material itself such as wafer defects, resulting in light intensity measurement errors of the CCD sensor. It becomes a factor.

However, conventional methods have only been able to correct variations in sensitivity caused by variations in the characteristics of amplifiers in stages of a CCD sensor19.
Therefore, although it was possible to correct the sensitivity between each CCD sensor, the non-uniformity of the optical response of each photoelement (so-called PRNU
) and the non-uniformity of the dark current of each photoelement (so-called D
It was not possible to perform sensitivity correction between each photoelement using SNU).

The present invention is unique in view of the above points, and in addition to correcting the sensitivity between each solid-state sensor, it is also possible to correct the variation in sensitivity between each photoelement in each solid-state sensor, and it is possible to perform high-precision optical It is an object of the present invention to provide a method and device for correcting lachrymal sensitivity of a solid-state sensor that can realize a practical measuring device.

That is, the 41 features of the method of the present invention are that, in the sensitivity correction method for a solid-state sensor having a plurality of photoelements, the sensitivity characteristics with respect to the exposure amount of a reference photoelement selected as a sensitivity standard and other photoelements are determined in advance. When measuring the amount of light of the object to be measured, the output of each photoelement other than the reference photoelement is corrected based on the difference in sensitivity characteristics with respect to the reference photoelement.

In a solid-state sensor such as a CCD sensor, for example, 2048 photo elements are arranged in parallel with a distance of 13 μm between centers, and the sensitivity characteristic of each photo element is 0. Also, as shown by plotting the signal output (volts) of the photoelement on the vertical axis, it has linearity with respect to the exposure amount when used within the guaranteed operating frequency range. Therefore, the output V of each photoelement is the exposure it E
(It is expressed by a D-order function, but as mentioned above, there are differences in the photoresponse and dark current of the photoelements, and the constant of the D-order function differs depending on each element.

This can be expressed numerically as shown in equation (1) below.

v = A HE + B 1- (1) However, A4 + J is a constant for the first photoelement. Note that dark current is detected during non-exposure, and C
This is a signal component generated by heat in a CD sensor, and in FIG. 1, the value of the vertical axis intercept is 1. In equation (1), Bi represents this dark current. The photoresponsiveness is expressed by the slope of the straight line in FIG. 1 and Ai in equation (1). Since the Ai and B1 values are different for each photoelement,
Even when each photoelement is irradiated with light at the same amount of light, there are differences in output and differences in sensitivity.

In the present invention, the sensitivity characteristics of each potoelement are
i, Bi value and 11. is determined in advance, and when measuring the light amount of the object to be measured, the output of each photoelement is corrected to match the sensitivity characteristic of a reference photoelement j appropriately selected as a sensitivity reference. That is, in the method of the present invention, in the sensitivity correction method of a solid-state sensor having N photoelements, the sensitivity characteristic of each photoelement is expressed by the following formula, Prior to measuring the amount of light, the photoelement is exposed twice with different uniform exposure amounts, and the constants Ai and Bi of the above formula are determined from each output, and each output v1 of each photoelement at the time of measuring the amount of light is calculated as follows. It is a sexual characteristic that correction calculations are made according to the formula % formula %).

However, ■: Depth of photoelement E: Exposure amount Ai, Bi: Constant for the first photoelement (l=1.2...N) vi: Output after correction of photoelement 1 Aj, J: Constant for the reference photoelement j selected as a sensitivity standard In this case, one of the different uniform exposure amounts is zero light amount, and therefore the output of each photoelement at that time is due to the dark current. Good. This is because Bi can be found in direct correspondence to the output of the photoelement. Note that when the sensitivity characteristic of each photoelement is not expressed by the above equation (1) and another function is used, the above-mentioned exposure with different uniform exposure amounts is not necessarily limited to two times. The number of uniform exposures may be appropriately set depending on the number of constants used in the sensitivity characteristic equation to be set.

The present invention will be explained in detail below. Assume that the number of photo elements of the CCD sensor is N (N bits), and each photo element is uniformly illuminated with an exposure amount E. At that time, each photoelement l (i=1.2, -, N: t'=
The output Vi of the photoelement j) and the output Vj of the reference photoelement j selected as the sensitivity standard are expressed by the following equations (2) and (3).

vl = AiE+Bi − (2) vj
=AiE+J (3) Since the output of another photoelement i is adapted to VC using the sensitivity characteristic of photoelement j as a reference, at the exposure amount E, the output Vi of photoelement l is equal to the reference photoelement j. should be corrected to the output Vj. This correction formula is expressed by the following formula (4).

Vs = (Aj/Ai)vt Tocho-(Aj/Ai)B
1=14), that is, the actual output v 1 (
= AI F +81) into equation (4), Vs
=vj (=AjE+J), and the corrected outputs of photoelement 1 vi IIJ', v jy (match. Therefore, when measuring the light amount of the measurement target with the CCD sensor, each photoelement) i (1 = 1.2. -N:l”(j
) is corrected according to equation (4), the exposure amount is converted into voltage for all photoelements using the sensitivity characteristics of photoelement j.9 This means that variations in sensitivity can be corrected. I can do it.

Therefore, in order to perform the correction calculation based on equation (4), the constant A
It is necessary to obtain i and J (including Aj and Bj) in advance, and to obtain the sensitivity characteristics of each photoelement. Therefore, before measuring the light amount of the measurement target, each photoelement of the CCD sensor is exposed twice with different uniform exposure amounts.
From each output of each photoelement at that time, Ai, J f
calculate. In this case, it is better to make one of the two uniform exposures with zero exposure, that is, detect the output of each photoelement in a dark state during non-exposure, and calculate the dark current component Bi directly from this output. . Then, from equation (2) # (3), E
By eliminating , the following equation (5) is obtained, and Aj/At=(v
j-J)/(vt-Bt) =-(5) From the output v1 and Vj of each photoelement in another uniform exposure (IE light star is not zero), A j according to equation (5)
Determining /A l Next, a sensitivity correction device capable of performing the sensitivity correction as described above will be described. Figure 2 shows the MTF
FIG. 2 is a block diagram showing one embodiment of the sensitivity correction device of the present invention incorporated in a Fourier calculation circuit of an inspection machine. In the Fourier calculation, it is necessary to use only the component that changes with exposure, that is, AiE, of the output signal of each photoelement, and exclude the dark current component Bi, which is the DC component of the signal. In the description, a device that performs vi-Bi correction will be described. Therefore, the correction equation of equation (4) is transformed as shown in equation (6) below.

ViJ=(/J/At)(vt Bi) −(6
) That is, from Aj/Ai and the dark current component Bi obtained in advance using equation (5), a correction calculation for Vi may be performed according to equation (6).

In the example shown in FIG. 2, six 256-bit CCD sensors 100 are arranged in parallel, and each CCD sensor 100 is connected in parallel to the hammer filter 101, and each photoelement 1 (1=(1 to 256) ) is input to a data RAM 104 via a sample-and-hold circuit 102 and an analog/f-digital converter (hereinafter abbreviated as ADC) 103, and is stored therein.

The output of the data RAM 104 is input to an adder/subtractor 110 and a multiplier 111.
The output of is input to the arithmetic unit 113 via the input port 112. The output end of the arithmetic device 113 is the output port 11
4, data RAM 104, constant RAM 106
and constant RAM 108 , constant RAM 106
, 108 (Q output is added/subtracted by adder/subtractor 110 and multiplier 11
1 is entered. Constant RAM 106
is a RAM for storing the correction constants Aj/Ai and Bl; p1 constant RAM 108 is a sin
and eoll tables are stored. 105
, 107 and 109 are the data RAM 104 and the constant R, respectively.
AM106 and constant RAM 108) 7 dress counters. In addition, as shown in the figure, there are gates 01 to 01 between the circuits.
G14 is installed, and each of the keys G1 to G14 is normally closed and is controlled to open and close by a controller (not shown). In addition, the adder/subtractor 110 via G9
The signal input to is a zero signal.

Next, the operation of this sensitivity correction device will be explained.

(1) When calculating each correction constant prior to MTF measurement.

(1) Uniformly expose each photoelement of the six CCD sensors 100 with the same amount of exposure, open r-)Gl and G3, and output v1(l=(1-256)X) of each photoelement t.
6) is stored in the data RAM 104.

(2) Then, close Gl and G3, and open gate G.
9 and G12 are opened to input the stored contents of the data RAM 104 to the arithmetic unit 113 via the input port 112.

(3) Then, close the gates G9 and G12, set the CCD sensor 100 to zero exposure, that is, the dark state, and open Gl and G3 to output B of each photoelement l.
i (1=(1~256)X6) as data RAM 104
, and rewrite the stored contents of the data RAM 104 with J.

(4) Next, close darts G1 and G3, and gate G9
and G12 is opened to input the stored contents of the data RAM 104 to the arithmetic unit 113 via the input port 112.

(5) The arithmetic unit 113 calculates (4 ) Aj/A4 is calculated according to the formula, and the obtained Aj/A4 and Bi are stored in, for example, a floppy disk. G9 and G12 are arithmetic unit 1
13 is closed after reading the data.

ω) When correcting the output of each photoelement in MTF measurement (1) The calculation device 113 looks at the A j/A 1 and Bi values stored on the floppy disk, and calculates f-
) Open G14 and G4 and save these values to constant RAM10.
Store in 6. Furthermore, as is clear from the above, the constant R
AM 106 has six CCD sensors 100 each with 25
Since it is 6 bits, it has 256x6x2 addresses.

Then, close G14 and G4.

(2) Gates G1 and G3 are opened, and the output v1 of each photoelement of the CCD sensor 100 receiving exposure from the measurement object is input to the data TtAM 104 and stored. Then, gates G1 and G3 are closed.

(3) Goo) Open GIO, G2 and G3, and data R
Output Vi stored in AM104 and constant RAM
106 and the constant 61 stored in the adder/subtractor 1.
10 to calculate vl-J, input the calculation result to the data RAM 104, and input the calculation result to the data RAM 104.
Rewrite the store contents with vI-J. And r-)
Close GIO, G2 and G3.

(4) Open gates G7, G6 and G3, and data R
vl-J value stored in AM104 and constant RA
The constant jJ/AH stored in M106 is passed through the multiplier 111 to calculate equation (6), and the result of the calculation is input to the data RAM 104.
Store contents of 104 (Aj/At) (vi B
i) Rewrite as [see equation (6)]. Then close G7, G6 and G3.

The contents stored in the data RAM 104 at this point are the contents of each photoelement (A4/jJ).
) (vt −Bt ), and the result of correcting the actual measured value vl of the output according to equation (6) is the data ItAM
1.04. Therefore, 1.04 K of data RAM is stored (Aj/j
J) (vt - nt) and the sin and coa tables stored in the constant RAM 108 are multiplied by the multiplier 111 by opening gates G8 and G13, and then input to the arithmetic unit 113.
The MTF test results may be obtained by performing necessary calculations such as Fourier calculations using the MTF test program built in 3.

The opening/closing operations of G1 to G14 as described above can be performed by a controller using a microcomputer or the like. One example is shown in FIGS. 3 to 6.

FIG. 3 is a block diagram illustrating data input/output control by the controller 120, and FIGS. 4 to 6 are timing diagrams of the control. For the sake of simplicity, the CCD sensor 100 is illustrated using, for example, one 256-bit sensor (7).
Components that are the same as those in FIG. 2 are given the same reference numerals. In Figure 3,
121 is an output circuit for the unit signal "]-, and 122 is a word/word output circuit.
It is a counter. -Also, 1 is a data bus, and 2~
19 is a path for transmitting control signals from the controller 120 to each circuit, and 20 to 24 are paths for transmitting various commands to the controller 120.

Then, from the path 20, a command to read the output of the CCD sensor 100 into the data RAM 104 is sent to the controller 1.
20, the CCD
The output Vi of the 256 photo elements of the sensor 100 (
(at zero light amount and during exposure with uniform light amount) is stored in the data RAM 104.
Store in. Next, the contents of the data RAM 104 are input to the arithmetic unit 113 to calculate A j/A l, and then A j/A1 and B5 are stored in the constant RAM 106.

When measuring MTF, similarly, at the timing shown in FIG. 4, the output Vi of each photoelement of the CCD sensor 100 to which the measurement target is exposed is read into the data RAM 104, and
At the timing shown in FIG. 5, this vl and constant RAM 1
ViBi is calculated from Bi of 06, and the calculation result is stored in the data RAM 104. Then, at the timing shown in FIG. 6, vl-J stored in the data RAM 104 is multiplied by Aj/A4 in the constant RAM 106, and the multiplication result is stored in the data RAM 104. As described above, during MTF measurement, the actually measured output Vi is subjected to a correction calculation according to equation (6), and the corrected output Vl-B is obtained as the stored content of the data RAMl0I.

Each photoelement i(
The output Vi of i) must match the sensitivity characteristics of the reference photoelement j. If the exposure amount is uniform, the output signals will all have the same output value, and the 11 degree variation between each photoelement due to variation in photoresponsivity and dark current in each photoelement is corrected. It is possible to perform highly accurate optical needle-side processing using a solid-state sensor to which the sensitivity correction of the present invention is applied.

Note that the present invention is not limited to the specific embodiments described above, and the present invention is applicable not only to CCD sensors but also to solid-state sensors having a plurality of photoelements. Of course, various modifications are possible within the technical scope.

[Brief explanation of the drawing]

Figure 1 is a graph showing the 1 quotient characteristic of the photoelement.
FIG. 2 is a block diagram showing one embodiment of the device of the present invention, and FIG.
The figure is a block diagram explaining the data transfer function of the controller, and FIGS. 4 to 6 are data control timing diagrams of the controller. (Explanation of symbols) 1...Data bus 100...CCD sensor 10
3... Analog/digital converter 104... Data RAM 106... Constant RAM 110... Addition/subtraction device 111... Multiplier 113... Arithmetic unit
120... Controller patent applicant Ricoh Co., Ltd. Agent Masaaki Kobashi ・No. 1
Figure exposure amount E

Claims (1)

[Claims] 1. In a sensitivity correction method for a solid-state sensor having a plurality of photoelements, sensitivity characteristics with respect to the exposure amount of a reference photoelement selected as a sensitivity standard and other photoelements are determined in advance, and 1. A method for correcting the sensitivity of a solid-state sensor, comprising: correcting the output of each photoelement other than the reference photoelement based on the difference in sensitivity characteristics with respect to the reference photoelement when measuring the amount of light. 2. In the sensitivity correction method for a solid-state sensor having N photoelements, the sensitivity characteristics of each photoelement are expressed by the following formula: v=AiE+Bi Prior to measuring the light amount of the measurement target, each of the photoelements is calculated with different uniform exposure amounts. It is characterized in that the constants Ai and Bi of the above formula are determined from the respective outputs of two exposures, and each output 'Vi of each photoelement at the time of light 11 measurement is corrected according to the following formula. Sensitivity correction method for solid-state sensors. However, v: photoelement blade E: exposure amount Ai, Bi: constant for the first photoelement (t=1, 2...N) l: l: output Aj, Bj after photoelement correction :
Constant 3 for the reference photoelement j selected as a sensitivity reference, in the second term above, the different uniform exposure amounts are:
A solid-state sensor sensitivity correction method characterized in that one of the methods is zero light amount. 4. A converter that is connected to a solid-state sensor having a plurality of photo elements and converts the output of each photo element from analog to digital; and a converter that converts the output of each photo element from analog to digital; A calculation device that inputs each blade and calculates a supplementary IF constant based on the sensitivity characteristics of each photoelement, a storage device that stores the calculation results of the calculation device, and each output of each photoelement when measuring the light amount of the measurement target. and a correction calculation device that performs a correction calculation based on the correction constant stored in the storage device. 5. In the above item 4, the correction constants are constants Aj/Ai and Bj (A3/A1
) A sensitivity correction device for a solid-state sensor, characterized in that it is B1. Then, A1+Iil: Constant for 'th photoelement (i'''1 r 2 r...N) N:
Number of photoelements Aj, Bi: Constant 6 for the reference photoelement H selected as a standard of 1 m degrees. A sensitivity correction device i/7' for a solid-state sensor, characterized in that a correction calculation is performed according to the following. Vi-(Aj/At) vH+Bj (Aj/AI
) Bi, where vi: Output cuff after correction of photoelement l. A sensitivity correction device for a solid-state sensor, wherein the adder/subtractor inputs the multiplication result of the multiplier and the memory content of the storage device. 8. In the above item 4, the different uniform exposure amounts are:
A sensitivity compensation device for a solid-state sensor, characterized in that one of the components is a zero element quantity.