JPS58177023A - Automatic gain controlling circuit - Google Patents

Abstract

PURPOSE:To obtain an output of high accuracy, by providing an AGC element and an adder/subtrator, using this control circuit for an optical measuring device using an image sensor and correcting uneven sensitivity of each photoelectric element of the image sensor. CONSTITUTION:A subtractor 81 of an operation circuit 8 subtracts an input signal V0 from a set value alpha0V0(where; alphaV0 is signal measuring a reference light source by the image sensor, not shown), its output (alpha0-alpha)V0 and the input signal alphaV0 are divided at a divider 82, and multiplied by a factor of m into m(alpha0-alpha)/alpha and A/D-converted 9 into a digital signal and a correction value correcting the uneven sensitivity in response to each element of the image sensor is stored in a memory 10 via a switch SW. In case of the measurment, the content of the memory 10 is converted into an analog signal m(alpha0-alpha)/alpha at a D-A converter 11. It is multiplied with the input signal alphaV0 by a factor of 1/m by an AGC element 51 of an AGC circuit 5 into (alpha0-alpha)V0, the result is summed with the input signal alphaV0 by an adder/subtractor 52 into alpha0V0 as the desired output.

Description

[Detailed description of the invention] (1) Field of invention This relates to a gain control circuit (AGC circuit).

(2) Conventional technology I can do that.

However, each photoelectric element of an image sensor has variations in sensitivity, and although this output has a small change in gain, it is necessary to correct this to maintain a constant output.

For this reason, in patent application No. 56-145925, AGC
A method has been proposed that uses a circuit to correct uneven sensitivity of an image sensor of an optical measuring device.

Further improvements need to be made in order to perform highly accurate correction.

(3) Purpose of the Invention In view of one or more points, the purpose of the present invention is to provide an automatic gain control circuit suitable for use in gain control with a small gain change range.

(4) Principle of the invention In an image sensor such as a COD, a plurality of photoelectric elements and a shift register for addressing are formed on one substrate, and the output of each element is sequentially transferred as a video signal by line transfer. Although it can be removed, each element is shown in Figure 1 (a).
), Φ) shows uneven sensitivity.

For this reason, the AGC circuit uses the representative output of each element as α■0
It is necessary to use this output αVo as an input and perform K so that αoVo is obtained for all elements.

(Here, Vo is the incident intensity [4-, g is the sensitivity JIx of each element.

is the required predetermined sensitivity. As will be explained later, the sensitivity α
, α0 may be considered as a gain. ) The principle of the AGC circuit of this invention is as follows.

As shown in Fig. 1 (a), Φ), the variation in the predetermined sensitivity a is caused by a variation of +Δσ in the base amount α0, which is the desired sensitivity, and if this ±Δα is corrected, good.

From FIGS. 1(a) and (b), if the difference between sensitivity α and aQ is Δa, the following formula holds true.

α0=α1Δα °°゛°°゛°°°゛°゛°°°°°゛°directυα = α0+Δα …
………………(2) To set the input signal αvO to αoV, input signal αV.

What is necessary is to multiply by α0/α.

Therefore, (1), (2) expressions: 1±α′ Song...Scream...Scream...(3
) holds true, so α′=□ □ ...knock ... ...knock - -
(4), +1. This is the output signal eo.

eo=-・gVo=(1±α′)αV.

=αVo -1--1・αVo ・・・old・・・
...(5), and the calculation as shown in equation (5) can be performed by the AGC circuit.

By the way, the effective operating range of AGC elements such as multipliers and FETs used in AGC circuits is often limited.
However, it still has a large error compared to linear ICs, etc. 2 It is usually difficult to perform high-precision calculations. Therefore, by focusing on the correction value l in equation (5), that is, the narrow AGC range, and performing AGC operation by expanding this AGC range,
It is preferable to reduce the influence of the calculation error of the AGC element on the final output. Rewrite equation (5) as a quadratic equation.

In order to maximize the effective operating range of the AGC element, the AGC range is expanded by m times and the coefficient □-m
The input signal αVO may be multiplied by the input signal αVO, the gain may be controlled, and this may be multiplied by one and added to the input signal.

Note that by transforming equation (5), eO=αVo−□・α■0 ・・・・・・・・・
...(5)', and the calculation may be performed based on this equation (5)'.

Note that the above description has been made by taking the sensitivity correction of an image sensor as an example, but this applies to general signal processing.

Assume that the desired gain is go and the predetermined gain is α, (5).

Automatic gain control calculations such as those shown in equations (5)' and (7) may be performed. This is particularly effective when the gain fluctuation range is small. All you have to do is perform a calculation similar to the linear equation.

eo = Aei′+ (Ao A) eI---(
8) eo = Ae+-)m(Ao-A) -et-
−−・−・−(9) Here, 61 is the input signal, eo
is the output signal, Ao is the gain you want to obtain, A is the predetermined gain 2m
is a coefficient for changing the gain in order to maximize the effective operation range of the AGO element. In equation (8), A=
If you think of l.

eo = el + (Ao-1) e'= Ao e
I......Scream...(8)
', the shape is easy to read, and calculations are also easy.

(5) Embodiments of the Invention First, an optical measuring device to which the present invention is applied will be described with reference to FIG.

In the figure, 1 is a measurement object, 2 is a lens that collects the radiant energy from the measurement object 1, and 3 receives the radiant energy that is collected by the lens 2.

The outputs of the plurality of photoelectric elements are sequentially transferred as video signals. A line transfer or surface transfer image sensor; 4 is a preamplifier that amplifies the output of the image sensor 3; 5 is an automatic gain control circuit (AGC circuit) having an automatic gain control function that amplifies the output el of the preamplifier 4; 6 is an output amplifier that takes out the output eo of the AGC circuit 5 from the output terminal 7;
8 is an arithmetic circuit that calculates the above-mentioned coefficient α' from the output ei of the preamplifier 4; 9 is an A-D converter that converts the output of the arithmetic circuit 8 into a digital signal; Sw is an A-D converter 9; A switch for taking out the output, and 10 a memory for storing the output of the A-D converter 9 taken out by the switch S--.

A D-A 11 converts the contents of the memory 10 into an analog signal and controls the gain of the fiAGc circuit 5 using its output eg.
Converter, 12 a drive circuit for driving the image sensor, 13 an arithmetic circuit 8. Memo') 10. Drive circuit 12
A control circuit that provides a control reference clock to the following devices performs secondary processing before the start of measurement.

Switch S- is closed, and a reference light source 1a, such as a surface light source with uniform radiation emittance, is placed at the position of the measurement object 1.

This reference light source 1a is measured by the image sensor 3.

The video signal for each photoelectric element of the image sensor 3 is as follows.

The output el is amplified by the preamplifier 4, and the arithmetic circuit 8 calculates the correction value α', and the A-D converter 9 converts it into a digital signal, which calculates the sensitivity unevenness corresponding to each photoelectric element of the image sensor 3. A correction value for correcting is stored in the memory IOK. This is because the sensitivity unevenness of each photoelectric element of the image sensor 3 is about ±10X.

If the desired sensitivity αO is set to 90% of the video signal eo, the correction range will be ±10%.
The capacity of 0 can be reduced by 1/10K. In addition, control circuit 1
3, a drive circuit 12 for the image sensor 3. memory 10
．． The timing of the arithmetic circuit 8 is determined. Then, as described above, the correction values corresponding to each photoelectric element of the image sensor 3 stored in the memory 10 are as follows.

During measurement, the signal EG is used by the DA converter 11 to control the AGC circuit 5.

Next, when measuring, open switch S# and image sensor 3
The radiant energy of the measurement object 1 is made incident on the object. The image sensor 3 outputs a time-series video signal corresponding to each photoelectric element, and correction of sensitivity unevenness corresponding to each photoelectric element is performed by D-A conversion of correction values stored in the memory 10 in advance. The output of the image sensor 3 is converted into an analog signal by the preamplifier 4, and the output of the image sensor 3 is amplified by the preamplifier 4, and the signal el is input as the control signal eg.
This is done by applying it to the GC circuit and controlling its gain. This correction is performed by converting the phantom control clock pulses of the control circuit 1 to the drive circuit 12 of the image sensor 3. By supplying the data to the memory 10, it is automatically performed for each photoelectric element of the image sensor 3. Then, this corrected signal eo is
The signal is taken out from the output terminal 7 via the output amplifier 6.

Next, the detailed configuration of the arithmetic circuit 8 and AGC circuit 5 will be explained with reference to FIG.

The signal when the image sensor 3 measures the reference light source is α
At this time, the subtracter 81 of the arithmetic circuit 8 subtracts the human input signal ago from the set value αoVo, and the output (α0−α)Vo and the input signal aVo are divided by the divider 8. The signal is calculated and multiplied by m to become m-(-0--)/-, which is converted into a digital signal by the A-D converter 9,
Coefficients as correction values for each element of the image sensor 39 are stored in the memo 'JIO via the switch S-.

During measurement, the contents of the memory 10 are transferred to the D-A converter 11.
Convert it into a digital analog signal m・(α0−α)/α.

AGC elements 51 such as FETs and multipliers of the AGC circuit 5 are used to obtain a desired output αoVo.

In this way, calculations such as the above-mentioned equations (5), (5γ, and (7)) can be performed.

(6) Summary of the Invention This invention provides an AGC element that is supplied with an input signal and controls the gain according to the difference between a desired gain and a predetermined gain, and an addition/subtraction system that adds and subtracts the output of the AGC element and the input signal. This is an automatic gain control circuit with a

(7) Effects of the Invention ■ When used in an optical measuring device using an image sensor, sensitivity unevenness of each photoelectric element of the image sensor can be corrected with an extremely simple circuit.

The resolution of the image sensor can be significantly improved.

■Since only the sensitivity difference needs to be stored in the memory, its capacity can be small, and the bi+ number of the A-D converter and D-A [converter can be small.2. Highly accurate output can also be obtained.

■Even if the AGC element breaks down or malfunctions, the input before the AGC is output as is, so there is little effect on the output.

- Since the dynamic range of the AGC element can be widened, high calculation accuracy is possible.

■AGC range Δg in Figures 1 (a) and (b) = 20
If X, even if there is a 5% error in the AGC element, fi
The final error is 20/100 x 5/100 - 1/100, so the error is ultimately within 1%, resulting in high accuracy.

■The arithmetic circuit can be an analog circuit, does not require high precision, and is inexpensive.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram for explaining the operation, and FIGS. 2 and 3 are diagrams for explaining the configuration of an embodiment of the present invention. 3... Image sensor, 5... AGO circuit, 8...
- Arithmetic circuit, 9... A-D' converter, 10... Memory, 11... D-large converter, 13... Control circuit,
81...Subtractor. 82...Divider, 51...AGO element, 52...
Adder/subtractor patent applicant Chino Seisakusho Co., Ltd.□

Claims (1)

[Claims] 1. An AGC element to which an input signal is supplied and which controls the gain according to the difference between a desired gain and a predetermined gain. An automatic gain control circuit comprising: an adder/subtractor that adds or subtracts the output of the AGC element and the input signal. 2. Depending on the effective operating range of the AGC element. 2. The automatic gain control circuit according to claim 1, wherein the gain of said AGC element is changed. 3. The output of the image sensor is used as the input signal, and the gain correction value corresponding to the output of each photoelectric element of the image sensor when the image sensor measures the reference light source is stored in the memory and used. An automatic gain control circuit as claimed in claim 1 or 2.