JPS6156929B2 - - Google Patents

Description

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

In optical measurement devices such as MTF (modulation transfer function) inspection machines that inspect lens aberrations, etc., solid-state sensors such as CCD (charge coupled device) sensors are used to measure light intensity distribution. A CCD sensor, for example, consists of 2048 (2048 bits) photo elements arranged in parallel with a center-to-center distance of 13 μm, and transmits the output corresponding to the exposure amount of each photo element to a signal processing device to calculate the exposure amount distribution, etc. It is possible to measure. Therefore, the sensitivity characteristics of the photoelement have linearity within the guaranteed operating frequency range.
The output is expressed as a linear function with the exposure amount as a variable, but the output value includes not only an output component that increases or decreases in response to the exposure amount, but also a dark component that is detected even during non-exposure (zero exposure amount). There is a current component. This dark current varies among each photoelement, and also varies sensitively depending on the ambient temperature in which the CCD sensor is used, so it becomes a cause of error in light intensity measurement using the CCD sensor.

For this reason, in the past, means were employed to maintain the temperature of the CCD sensor constant or to correct the dark current component using an electric circuit, in an attempt to eliminate the light amount measurement error. However, in the former,
Strict temperature control is not possible when the CCD sensor is air-cooled, and when the CCD sensor is kept at a constant temperature by bringing a temperature sensor or a temperature control element such as a Peltier effect element into contact with the CCD sensor.
A large number of CCD sensors (e.g. 12
2) is extremely expensive and impractical. In the latter case, during the period when only dark current is output from the CCD sensor by opening and closing the switch circuit, connect it to a capacitor and charge it, store the dark current as the potential difference of the capacitor, and measure the light intensity of the CCD sensor. There are means to correct the output, but since this potential difference is only the average level of dark current for each CCD sensor,
It was not possible to correct the variation in dark current between each photoelement.

The present invention has been developed in view of the above points, and is capable of highly accurate correction of dark current components that vary between photoelements and also vary with temperature, and that directly affects the amount of exposure. It is an object of the present invention to provide a temperature correction method and apparatus for a solid-state sensor that can extract only the corresponding output component and that can be implemented at low cost. That is, the method of the present invention is characterized in that, in the temperature correction method for a solid-state sensor having a plurality of detection photoelements for detecting the amount of light, a reference photoelectron that outputs substantially only dark current is provided in the vicinity of the detection photoelement. Calculate the dark current component of the detection photoelement during light intensity measurement based on the output of the detection photoelement and reference photoelement in a non-exposed state at a reference temperature and the output of the reference photoelement during light intensity measurement. However, the output of the detection photoelement is corrected by the dark current component.
The device of the present invention also includes a solid-state sensor having a plurality of detection photoelements for detecting the amount of light and at least one reference photoelement that is disposed near the detection photoelements and outputs substantially only dark current. , a converter connected to the solid-state sensor and converting the output of each photoelement from analog to digital; output Vi (T ₀ ) of the detection photoelement in a non-exposed state at a reference temperature T ₀ and output V ₀ of the reference photoelement; (T ₀ ), a temperature constant is calculated from the output V ₀ (T) of the reference photoelement at the time of light intensity measurement at temperature T, and the V ₀ (T ₀ ) stored in the storage device. a computing device;
The dark current component of the output Vi (T) of the detection photoelement during light intensity measurement is calculated from the temperature constant and the Vi (T ₀ ) stored in the storage device, and the output Vi (T) is calculated as the dark current component. The present invention is characterized in that it has a correction calculation device that performs correction according to the following.

First, the principle of temperature correction of the output of each photoelement in the present invention will be explained. Solid-state sensors such as CCD sensors, for example, have N (2048) photoelements arranged side by side with a center-to-center distance of 13μm, but the sensitivity characteristics of each photoelement vary with respect to the exposure amount within the guaranteed operating frequency range. It has linearity, and the output Vi of each photoelement is expressed as a linear function of the exposure amount E as shown in equation (1) below.

Vi=AiE+Bi...(1) However, Vi: Output of the i-th photoelement (i=1, 2,...N) E: Exposure amount Ai: Constant indicating the photoresponsiveness of photoelement i Bi: Photoresponse of photoelement i Dark current component It is shown that the dark current Bi is expressed by an exponential function with respect to temperature from its generation mechanism, and Bi is expressed as shown in equation (2) below.

Bi(T)=Bi(T ₀ )・2〓〓〓〓 …(2) However, Bi(T) : Dark current component at temperature T Bi(T ₀ ): Dark current component at reference temperature (T ₀ ), i.e. , when the temperature T rises by 8° C. from the reference temperature T ₀ , the dark current Bi(T) increases to twice the dark current Bi(T ₀ ) at the reference temperature T ₀ .

Therefore, in the present invention, in addition to the detection photoelements arranged in parallel as many as the number of bits (for example, 2048) necessary for detecting the amount of light, at least one reference photoelement is arranged near this detection photoelement. do. The reference photoelement has its light detection surface coated with metal or the like, so even if the CCD sensor is irradiated with light, the reference photoelement is not exposed and always outputs only the dark current component. by the way,
Also for the reference photoelement, its dark current B ₀
is an exponential function related to temperature and is expressed as in equation (3) below.

B ₀ (T) = B ₀ (T ₀ )・2〓〓〓〓 …(3) However, B ₀ (T): Dark current component at temperature T B ₀ (T ₀ ): Dark current at reference temperature T ₀ Then, the following equation (4) is established from equations (2) and (3).

Bi(T)={B ₀ (T)/B ₀ (T ₀ ))}・Bi(T ₀ )
...(4) Therefore, at an arbitrarily set reference temperature T ₀ and an exposure amount in a dark state, the output Vi (T ₀ ) of the detection photoelement and the output V ₀ of the reference photoelement
Bi (T _{0 )} and B ₀ (T ₀ ) are obtained in advance by measuring (T 0 ), and when measuring the light amount (temperature T of the solid-state sensor), the output of a reference photoelement that outputs only the dark current component is By measuring V ₀ (T), finding the dark current B ₀ (T) at the temperature T at that time, and calculating these data according to equation (4), the detection at the temperature T when measuring the amount of light can be performed. The dark current Bi(T) of the photoelement can be calculated.

That is, if the constant k is defined as in equation (5) below, k=B ₀ (T)/B ₀ (T ₀ )...(5) Equation (4) is transformed as in equation (6) below.

Bi(T)=k・Bi(T ₀ )...(6) Therefore, at an arbitrary reference temperature T ₀ , the outputs Vi(T ₀ ) and V ₀ (T ₀ ) of each photoelement in the non-exposed state are determined in advance. When measured, these correspond to Bi (T ₀ ) and B ₀ (T ₀ ), respectively. Then, store this data, and when measuring the light amount of the CCD sensor (temperature T), the output of the reference photoelement V ₀
By actually measuring only (T), this can be determined as Bo
(T), so by calculating the temperature constant k according to equation (5) and performing the calculation according to equation (6), the dark current component Bi (T) of the output Vi (T) of all detection photoelements is calculated. can be calculated with high precision.
Therefore, when Bi (T) is subtracted from the output Vi (T) of the detection photoelement when measuring the light amount, as is clear from equation (1), the photoresponse component AiE of the output Vi (T) that directly corresponds to the exposure amount This AiE is unaffected by variations in dark current between each photoelement and fluctuations in dark current due to temperature changes, so by measuring the light intensity distribution based on the AiE component, Highly accurate optical measurements can be performed.

Next, a temperature correction device for performing the temperature correction as described above will be explained. 1 is a block diagram of the CCD sensor 100, FIG. 2 is a time chart of the operation, FIG. 3 is a block diagram showing one embodiment of the present invention, and FIG. 4 is a flow chart of the correction calculation device 115. . In the CCD sensor 100, N (for example, 2048) detection photoelements 2 are arranged in a row, and four reference photoelements 1 are arranged on both sides of the arrangement direction through separation photoelements 3.
They are arranged side by side. As described above, the reference photoelement 1 has its photodetecting surface coated with a metal or the like to shield light, and always outputs only the dark current component. A transfer gate 4 is arranged near each of these photoelements 1, 2, and 3 along the direction in which they are arranged in parallel, and analog transport shift registers 5, 5 are arranged outside the transfer gate 4 and are connected to the transfer gate 4. They are arranged in parallel, and the output of each photoelement (hereinafter also referred to as video output) is sequentially sent from the analog transport shift register 5 to the output amplifier 9 via the charge detection circuit 8, and the video output is output. The signal is input from amplifier 9 to analog multiplexer 106 . In FIG. 1, 6 and 7 are an analog shift register and an analog EOS shift register, respectively, and 10 and 11 are a MOS circuit and an analog EOS shift register, respectively.
Showing EOS amplifier. analog multiplexer 1
CCD sensors 101, 102, 103, 104, and 105 similar to the CCD sensor 100 are connected to 06, and the output of each photoelement is inputted sequentially in the same way. For this purpose, a case will be described in which only the CCD sensor 100 is used.

In FIG. 2, φ _X is a transfer pulse, φ _T is a shift pulse, and _{φ R} is a reset pulse. When the transfer pulse _φ Video output is taken from the photoelement. The video output is an 8-bit blank signal followed by 4 bits, indicated by D in the figure.
This is followed by the output signal of the 4-bit reference photoelement 1, followed by the output signal (output zero) of the 4-bit separation photoelement 3 shown in the figure, and then the N-bit signal of the detection photoelement 2.
Therefore, by counting the reset pulse φ _R after the transfer pulse _φ

As shown in FIG. 3, the output of each photoelement of the CCD sensor 100 is input to an analog/digital converter (hereinafter abbreviated as ADC) 108 via a sample-and-hold circuit 107.
After being converted into a digital signal at step 8, it is temporarily stored in a register provided therein. ADC
The output of 108 is sent to data path 13 and input to an arithmetic storage device (not shown) via input port 122. The calculation storage device stores the output of each photoelement as input data, calculates the temperature constant k, and performs necessary calculations for MTF inspection based on the corrected photoelement output, For example, it is constituted by a computer or the like having a floppy disk as a storage means.

The data bus 13 includes RAM112 and RAM1.
14 are connected, and these are the outputs of each detection photoelement when measuring the light intensity of the MTF inspection target.
Vi (T) and the output Vi (T ₀ ) of each detection photoelement in a non-exposed state at a reference temperature T ₀ are stored. 111 and 113 are RAM 112 and
This is an address counter for the RAM 114. The temperature constant k calculated by the arithmetic storage device is output port 1.
21 to the register 110 via the data bus 13, and is temporarily stored there. The correction calculation device 115 uses the temperature constant k stored in the register 110, the detected photoelement output Vi (T) at the time of light intensity measurement stored in the RAM 112, and the RAM 1.
From the detection photoelement output Vi (T ₀ ) at the reference temperature stored in 14, the output Vi (T) of each detection photoelement at the time of light intensity measurement is corrected. It has an adder/subtractor 119 and an adder/subtractor 120. The control circuit 123 inputs the reading operation signal of the CCD sensor output, etc., and sends the control signal 10 to each of the above circuits.
This is a circuit that outputs .about.30 and controls input/output operations of each circuit. Note that 109 is a unit signal (“1”) generator.

Next, the operation of this temperature capture device will be explained.

() When setting the CCD sensor to the MTF inspection machine.

(1) Output of reference photoelement 1 of CCD sensor 100 (see Figure 1) to control circuit 123
When a reading command signal of V ₀ (T ₀ ) is output,
A sampling signal 10 synchronized with the operation timing of the CCD sensor (see Figure 2) is output from the control circuit 123 to the sample-and-hold circuit 107, and is further output to the ADC 108.
The ADC start signal 11 is output, and among the outputs of the CCD sensor 100, the reference photoelement 1
Only the output of is taken out, converted to a digital signal, and temporarily stored in the register of ADC 108.

(2) Next, when a command signal is output to the control circuit 123 to transfer the memory contents of the ADC 108 to the input port 122, the output operation signal 12 is input from the control circuit 123 to the ADC 108, and the ADC 108 adjusts the temperature at the time of setting (reference). Output of reference photoelement 1 at temperature T ₀ )
V ₀ (T ₀ ) is sent to the data bus 13, and V ₀
(T ₀ ) is read into the arithmetic unit via the input port 122.

(3) Then, the exposure amount of the CCD sensor 100 is set to zero, the detection photoelement 2 is placed in a non-exposed state, and an operation command signal is output to the control circuit 123, and the operations are performed in the same manner as in (1) and (2) above. Then, the output Vi (T ₀ ) of each detection photoelement 2 in the non-exposed state at the reference temperature T ₀ is read into the arithmetic unit and stored.

() When measuring the light intensity of the lens under test for MTF inspection.

(1) The output Vi (T ₀ ) of the detection photoelement stored in the arithmetic unit is input to the RAM 114 via the output port 121 and stored.

(2) In the same way as the operations in (), (1), and (2) above,
The output V ₀ (T) of the reference photoelement at the time of MTF inspection (during light intensity measurement) is read into the calculation device. This V ₀ (T) and V ₀ (T ₀ ) stored in the arithmetic unit are respectively B ₀ in the equation (5) above.
Since (T) and B ₀ (T ₀ ) match, the arithmetic unit calculates the ratio of V ₀ (T) and V ₀ (T ₀ ) and calculates (5)
Calculate the temperature constant k of the equation. Then, this temperature constant k is sent to the data bus 13 via the output port 121 and stored in the register 110.

(3) By the same operation as (), (1), and (2) above,
Video signal of CCD sensor 100 during MTF inspection, i.e. output Vi of detection photoelement 2
Read (T) and pass through data bus 13.
Store it in RAM112.

(4) Next, the correction calculation device 115 reads register 1.
10. Calculate the dark current component Bi (T) of the output Vi (T) of the detection photoelement from each data stored in RAM 112 and RAM 114, and calculate the dark current component Bi (T) of the output Vi (T) of the detection photoelement, and directly calculate the amount of exposure by excluding Bi (T) from Vi (T). Find the corresponding photoresponse component AiE. That is, since Vi (T ₀ ) is the output in the non-exposed state, it matches Bi (T ₀ ) in the equation (6), and Bi (T) is calculated according to the equation (6). And Vi(T)
-Calculate AiE by calculating Bi(T).

Next, the operation of this correction calculation device 115 will be explained based on the flowchart of FIG. 4. First, from the control circuit 123 to the address counter 111
Load signals 18 and 21 are output to the counters 111 and 113, respectively, and the leading address is set in the address counters 111 and 113. Next, the output operation signal 19 is inputted to the RAM 112, Vi(T) related to the first detected photoelement among the stored contents Vi(T) of the RAM 112 is sent to the data bus 13, and a load signal is sent to the correction calculation device 115. 24 is input, and Vi(T) is input from the data bus 13 to the register 116 and latched. Similarly, the unit signal "1" is latched in the register 117 by the output operation signal 14 to the unit signal generator 109 and the load signal 25 to the correction arithmetic unit. Then, by inputting the load signal 26 to the correction arithmetic unit 115, the stored contents of the register 116 and the stored contents of the register 117 are multiplied, and the multiplication result I·Vi(T) is latched in the register 118.

Next, the output operation signal 22 is input to the RAM 114, and the stored content V ₁ (T ₀ ) of the RAM 114 is sent to the data bus 13 and latched into the register 116 by the load signal 24. Furthermore, the stored contents k are sent to the data bus 13 by the output operation signal 16 to the register 110, and latched into the register 117 by the load signal 25. Then, V ₁ (T ₀ ) in the register 116 and k in the register 117 are multiplied by the load signal 26 and the addition/subtraction control signal 28 , and the multiplication result k・
From V ₁ (T ₀ ) and 1·V ₁ (T) latched in register 118, 1·V ₁ (T)−k·V ₁
(T ₀ ) is calculated, this is latched in the register 118, and the stored contents are V ₁ (T)−kV ₁ (T ₀ )
can be rewritten as Next, when the output operation signal 27 is input, the stored contents of this register 118 are sent to the data bus 13, and the chip operation signal 27 is sent to the data bus 13.
9 and a RAM into which the read operation signal 30 is input.
112. And count signal 1
7 and 20 are address counters 111 and 1, respectively.
13, address counters 111 and 1
The address of 13 is incremented. Then, the output operation signal 19 is input again to the ram 112, and
The above operations are repeated for the th detected photoelement. And the number of repetitions is
When the number of bits N of the CCD sensor 100, ie, the number N of detection photoelements 2, is reached, the operation of the correction calculation device 115 is stopped.

In this case, the content stored in the RAM 112 is the output Vi (T) of the detection photoelement at the temperature T during the MTF test minus the dark current component Bi (T) at that temperature (Vi
(T) - Bi (T) = AiE), and only the photoresponse component that directly corresponds to the exposure amount of each detection photoelement is
This is determined as the memory content of the RAM 112. Therefore, if the light intensity distribution of the CCD sensor is determined based on this, highly accurate optical measurement can be performed that is unaffected by variations in dark current components between photoelements and temperature fluctuations.

As explained in detail above, according to the present invention, the CCD
From the output of each detection photoelement of the sensor, the dark current component, which varies between each photoelement and doubles with temperature rise of 8℃, is corrected with extremely high accuracy for temperature. Since this can be excluded and only the components that directly correspond to the exposure amount can be extracted, and this can be carried out using an extremely simple calculation process and device, the present invention can be applied to the MTF.
When applied to optical measuring devices such as inspection machines, extremely high precision optical measurement is possible.

Note that the present invention should not be limited to the specific embodiments described above, and various modifications are possible within the technical scope of the present invention. In particular, the present invention corrects the output by determining the output temperature change from the reference temperature of the detection photoelement based on the output temperature change of a reference photoelement that always outputs substantially only the dark current component. Therefore, the calculation process for the correction calculation is not limited to that shown in the above embodiment. for example,
The ratio Vi (T ₀ )/V ₀ (T ₀ ) of the output Vi (T _{0 ) of the detection photoelement in the non-exposed state at the reference temperature and the output V 0 (} T ₀ ) of the reference photoelement is calculated in advance. is stored, and the product of the output V ₀ (T) of the reference photoelement and the above ratio is calculated when measuring the amount of light to calculate the dark current component Bi(T) of the detection photoelement when measuring the amount of light. Good too.

[Brief explanation of the drawing]

1 is a block diagram of the CCD sensor 100, FIG. 2 is a time chart of the operation, FIG. 3 is a block diagram showing one embodiment of the present invention, and FIG. 4 is a flow chart of the correction calculation device 115. . Explanation of symbols: 1...Reference photoelement, 2...Detection photoelement, 100...CCD sensor, 10
8...Analog/digital converter, 110, 11
6,117,118...Register, 112,114
...RAM, 115...correction calculation device, 119...multiplier, 120...adder.

Claims (1)

[Scope of Claims] 1. In a temperature correction method for a solid-state sensor having a plurality of detection photoelements for detecting light amount, a reference photoelement that substantially outputs only dark current is disposed near the detection photoelement. , calculate the dark current component of the detection photoelement during light intensity measurement based on the output of the detection photoelement and reference photoelement in the non-exposed state and the output of the reference photoelement during light intensity measurement, and calculate the output of the detection photoelement. A temperature correction method for a solid-state sensor, characterized in that the temperature is corrected by the dark current component. 2. A solid-state sensor having a plurality of detection photo-elements for detecting the amount of light and at least one reference photo-element disposed near the detection photo-element and outputting substantially only dark current, and connected to the solid-state sensor. The output of each photoelement is converted to analog/
Converter for digital conversion and output V _i of the detection photoelement in non-exposed state at reference temperature T ₀
(T ₀ ) and _an output V ₀ (T ₀ ) of a reference photoelement; an arithmetic device that calculates a temperature constant from V ₀ (T ₀ ); and an output V _i of the detection photoelement during light intensity measurement from the temperature constant and the V _i (T ₀ ) stored in the storage device;
A temperature correction device for a solid-state sensor, comprising: a correction calculation device that calculates a dark current component of (T) and corrects the output V _i (T) using the dark current component. 3 In the above item 2, the temperature constant is
The ratio of V ₀ (T) to the above V ₀ (T ₀ ) V ₀ (T)/V ₀
(T ₀ ), and the correction calculation device calculates the ratio V ₀
A temperature correction device for a solid-state sensor, characterized in that the dark current component B _i (T) is calculated by multiplying (T)/V ₀ (T ₀ ) by the V _i (T ₀ ). 4 In the above paragraph 3, the correction calculation device:
The dark current component Bi (T) is subtracted from the output Vi (T) of the detection photoelement to obtain the output Vi
A temperature correction device for a solid-state sensor, characterized in that it corrects (T).