JPS61118072A - Photodetecting sensor sensitivity correcting circuit - Google Patents

Abstract

PURPOSE:To prevent the deterioration of sensitivity correcting accuracy of the photodetecting sensor by inserting an amplifier of a variable gain and a level shift circuit into an input part of an A/D converter and installing the function to control a gain and a level shift quantity of these circuits. CONSTITUTION:A level shift circuit composed of an amplifier 3, a differential amplifier 4 and a D/A converter 5 is inserted between an amplifier 2 and an A/D converter 10 in a correcting circuit 6, and these actions are controlled at a control part 101. Secular changes occur at a photodetecting sensor 1 and a light source and an input voltage of the A/D converter 10 is changed, and then, a minimum input voltage of theA/D converter 10, in short, a dark signal VDO, and a maximum input voltage, in short, a bright signal VB, are also changed. Consequently, a correcting reference voltage VD and VB-VD stored in memories 20 and 21 are also changed. The control part 101 detects the direction and quantity of secular changes from the change of these correcting reference voltages, and the selection of an amplifying degree of an amplifier 3 and the impressing voltage of the differential amplifier 4 are determined so that the input voltage scope, which can be converted by the A/D converter 10, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a sensitivity correction circuit for a light receiving sensor.

[Background of the invention]

In a color facsimile transmitter or the like, at least three color signals are read from a document by a light receiving sensor, combined, and transmitted. The sensor and its light source are read in colors (usually red or blue).

Since the characteristics are different for each color (green) and there are large variations from one component to another, it is necessary to correct the output of the light receiving sensor for each color. Regarding the sensitivity correction circuit of this light receiving sensor, see Dejiri and Ota'! 4'/c, "Study of color photoelectric conversion circuit for contact type sensor" (Imaging Electronics Engineers of Japan, 1982), etc., and the main points of the circuit are based on the image signal level when the manuscript is full day. This normalizes each surface signal as a voltage.

FIG. 1 is a block diagram of a conventional sensitivity correction circuit for a light receiving sensor. To obtain a color image signal, it is necessary to read at least three color signals.

Normally, three colors are used: R (red), G (green), and B (blue), but since the correction operation is the same for R, G, and B, only one color (
Only R) will be described below.

The correction operation consists of a mode in which a sixth reference signal (a bright signal and a dark signal) is obtained for correction, and a mode in which an arbitrary image signal is digitally converted while being corrected based on the reference signal. First, when obtaining the inner dark signal vD of the reference signal, the light source is extinguished.

At this time, the signal VDO read from the light receiving sensor IK is amplified by the amplifier 2 and input to the A/D converter 10 in the correction circuit 6. At this time, the analog switch SR is closed by the control unit 100K, the resistor RR is connected to the amplifier 2, and the amplifier 2 is set to the amplification degree determined by the resistor RR. The degree of amplification is set so that the maximum value of the bright signal VaO, which will be explained later, becomes the maximum value of the convertible input range of A/D converter 2 (at this time, the input range of the A/D converter is used most effectively). It is set. The dark signal VDO input to the A/D converter 2 is converted into a digital signal VD and sent through a 3-state buffer 30 to a dark signal memo+720 (R, G,
Then, the light source is turned on to obtain a bright signal VB, and the white original or white reflective plate is read by the light receiving sensor 1. The read signal VBO is sent to the amplifier 2 in the same way as when reading the dark signal VDO.
．． It is converted into a digital signal VB via the A/D converter 10 and input to one input terminal of the subtracter 40.

In synchronization with this input, the previously stored dark signal VD is read out from the dark signal memory 20 and input to the other input terminal of the subtracter 40, and VB-VD is calculated. The result of this calculation is stored in the bright signal memory 21 via the 3-state buffer 31. As described above, a reference signal for correction was obtained. This reference signal is measured and updated when the power of the apparatus is turned on or every document page. Next, a process of obtaining a digital conversion signal VS while correcting an arbitrary image signal VSO based on the obtained basic signal will be explained. The image signal VS of an arbitrary document read by the light receiving sensor IK with the light source turned on is sent to the amplifier 2. The A/D converter 10 converts the digital signal VstK.

It is input to one input terminal of the subtracter 40. Also.

In synchronization with this signal, the dark signal VD is read out from the dark signal memory 20 and inputted to the other input terminal of the subtracter 40, where Vsl-VD is calculated and inputted to one input terminal of the multiplier 60. . In this manual synchronization, Va - VD is read out from the bright signal memory 21, inputted to the address of the ROM 50 which is the variation correction coefficient table, and multiplied by the corresponding correction coefficient (reciprocal of input VB - VD) from this ROM 50. input to the other input of the device 60 (Vs
A calculation output of l-VD)/(Va-VD), that is, a correction output VS is obtained.

In the conventional circuit as shown below, the accuracy of the correction output VS is A/
The conversion accuracy of the D converter 10 and the calculation accuracy of the digital calculation unit (depending on each other. The accuracy of the digital calculation unit is constant depending on the number of bits of calculation, but the conversion accuracy of the A/D converter 10 is different from that of the A/D converter. According to the input signal amplitude of 10. In other words, the conversion accuracy will be best if the entire convertible range of the A/D converter 10 is used.For this reason, an amplifier is However, the A/D converter 100 input changes due to aging of the light source and light receiving sensor, but this is not compensated for by the initial settings of amplifier 2, so the conversion accuracy deteriorates. There is.

[Purpose of the invention]

An object of the present invention is to provide a highly accurate light-receiving sensor sensitivity correction circuit that can prevent deterioration of the sensitivity correction accuracy of the light-receiving sensor due to secular changes such as a decrease in the light intensity of a light source and changes in the characteristics of a light-receiving element.

[Summary of the invention]

The present invention inserts a variable gain amplifier and a level shift circuit into the input section of the A/D converter, and also enables the dark signal level and bright signal level of the input signal to the A/D converter to The present invention is characterized in that a control function is provided to control the gain and level shift amount of these circuits so that they match the lower and upper limits of the convertible range.

[Embodiments of the invention]

The present invention will be explained below with reference to the embodiment shown in FIG. The configuration of the figure is such that the amplifier 3 and the differential amplifier 4 are connected between the amplifier 2 of FIG. 1 and the A/D converter 10 in the correction circuit 6.
A level shift circuit consisting of a converter 5 is inserted, and these operations are controlled by a control section 101.
The parts after the /D converter are the same as those shown in FIG. 1, but this part is omitted. In such a configuration, in an initial state without aging, the amplifier 3 is set so that the amplification degree is 1 (analog switch S+ is closed and R1 is connected) by the control unit 101.

Further, a voltage is set at the negative input terminal of the differential amplifier 4 via the D/A converter 5 so that the differential amplifier 4 also functions as an amplifier with a simple amplification factor of 1. When the light receiving sensor 1 and the light source (not shown) change over time and the input voltage of the A/D converter 100 changes, the minimum input voltage, that is, the dark signal vDo, and the maximum input voltage, that is, the bright signal VBO of the A/D converter 10 also change. do. Accordingly, the corrected reference voltages VD and VB-VD output from the A/D converter 10 and stored in the dark signal memory 20 and the bright signal memory 721 (FIG. 1) also change.

The control unit 101 detects the direction and amount of secular change from the changes in these corrected reference voltages, and depending on the result, controls the input voltage of the A/D converter 10 to be the same as the initial state, that is, the A/D converter 10 The amplification degree of the amplifier 3 and the voltage to be applied to the differential amplifier 4 are determined so that the convertible input voltage range is as follows.

Controls amplifiers 3 and 4. Note that the amplification factor of the amplifier 3 can be controlled by turning on any combination of analog switches Sl to Sn. In this way, in this embodiment, it is possible to detect aging of the light receiving sensor, etc., and to maintain the conversion accuracy of the A/D converter at the best condition at all times.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to compensate for the deterioration in conversion accuracy of the A/D converter due to secular changes such as a decrease in the light intensity of the light source and changes in the sensitivity characteristics of the light receiving element, and to maintain good light reception over a long period of time. This has the effect of correcting sensor sensitivity.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional sensitivity correction circuit for a light receiving sensor, and FIG. 2 is a diagram showing an embodiment of the sensitivity correction circuit according to the present invention. l... Light receiving sensor 2... Amplifier for correcting signal level difference between each color 3... Amplifier, 5... D/A converter 10... A/D
Converter 101...control unit.・＼、２／

Claims (1)

[Claims] A for digitizing the output of the light receiving sensor adjusted so that the output level for the three primary colors is the same
In the light receiving sensor sensitivity correction circuit, which consists of a /D converter and a standardization circuit that standardizes the output of the converter according to the bright signal level in the output of the converter, a gain is installed before the A/D converter. By providing an adjustment means and a level shift means, and further monitoring the output of the A/D converter, fluctuations in the light receiving sensor output due to aging are detected, and the input signal level to the A/D converter is adjusted to the initial level. A light-receiving sensor sensitivity correction circuit comprising control means for controlling the gain and level shift amount of the gain adjustment means and level shift means so as to be the same as when set.