JPH06311312A - Image sensor and reading method thereof - Google Patents

Abstract

PURPOSE:To provide the image sensor and reading method thereof in which a sensor output is latched in a predetermined way even when a luminous quantity of a light source is changed largely without slowing down the reading speed. CONSTITUTION:A luminous quantity sensor 26 senses a luminous quantity of a light source 27 and an illuminance calculation circuit 23 obtains an illuminance Em based on the sensed luminous quantity. A bias voltage application time calculation circuit 24 calculates a proper charge storage time ts of a light receiving elemment based on the illuminance Em and a proper luminous quantity Lo to control a bias voltage application time in a bias shift register 21 based on the stored time ts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor used in an image input device such as a facsimile, a scanner, a digital copying machine, an optical character reader (optical character reader), etc., without slowing the reading speed. The present invention relates to an image sensor capable of monitoring the light amount of a light source for illuminating an original and adjusting so as to obtain an appropriate sensor output, and a reading method thereof.

[0002]

2. Description of the Related Art Among image sensors used in conventional image input devices, there is an image sensor of a type in which a document is irradiated with light from an illumination lamp as a light source and the reflected light from the document is read. This type of image sensor has a problem in that proper reading cannot be performed when the light amount of the light source changes.

In order to solve this problem, Japanese Patent Laid-Open No. 1-11
As disclosed in Japanese Patent No. 65264, an image reading device has been proposed in which a photodetector monitors a part of the luminous flux of an illumination lamp and dimms light so that the output of the photodetector reaches a predetermined value. . As a result, even if the light amount of the light source is partially reduced or the sensitivity of the image sensor has a temperature characteristic, normal light control can be performed and shading correction can be normally operated.

Further, as disclosed in Japanese Patent Laid-Open No. 228875/1990, a reference density subject is irradiated prior to the scanning of the reading of the original document, and the reflected light from the reference density subject is received by the image pickup device to be predetermined. A document reading apparatus has been proposed in which the charge storage time of the image sensor is changed by a feedback operation so as to match the reference value. This makes it possible to obtain an image signal having excellent linearity / gradation and S / N ratio without preheating when the light amount of the light source is reduced at a low temperature.

[0005]

However, the above-mentioned conventional image or document reading device has the following problems. First, in the image reading device described in Japanese Patent Application Laid-Open No. 1-165264, there is a limit to the amount of light that can be dimmed using a dimming circuit. For example, in the case of a cold cathode tube, if the brightness at the brightest time is 100%, At most 100% to 60
There is a problem that the light control is possible within the range of about%, and the light control range of the light amount is limited.

On the other hand, there are cases where the amount of change in the amount of light of the illumination lamp, which is the light source, is larger than the range in which it can be kept constant by dimming. For example, as shown in FIG. %, When the brightness changes with time in the range of 20% to 100%, it becomes impossible to keep the light amount constant by light control, and as a result, the sensor output is kept constant as shown in FIG. There is a problem in that an undimmable area cannot be generated and the sensor output cannot be held constant.

Further, when light control is performed by the light control circuit, the light emission from the light source may become unstable when the light amount is reduced, which causes a problem that the flicker of the light source increases.

Next, in the document reading apparatus disclosed in Japanese Patent Laid-Open No. 2-228875, the charge accumulation time in the image pickup device is controlled by a feedback operation. However, there is a problem that scanning takes time.

The present invention has been made in view of the above circumstances, and the output of the sensor can be kept constant even when the amount of light is changed beyond the dimmable range by the dimming circuit, and the reading speed is further reduced. An object of the present invention is to provide an image sensor and a reading method thereof.

[0010]

According to a first aspect of the present invention for solving the above-mentioned problems of the conventional example, in an image sensor, a light amount detecting means for detecting the amount of light emitted from a light source, and the detected light amount. Illuminance calculation means for calculating the illuminance from the light quantity, storage time calculation means for calculating the charge storage time in the light receiving element from the calculated illuminance and a preset appropriate light quantity value, and the light reception according to the calculated storage time. And a bias voltage control means for controlling the application time of the bias voltage applied to the element.

According to a second aspect of the present invention for solving the problems of the conventional example, in the image sensor reading method, the amount of light emitted from the light source is detected, the illuminance is calculated from the detected amount of light, and the illuminance is calculated. A feature is that the charge accumulation time in the light receiving element is calculated from the calculated illuminance and the preset appropriate light amount value, and the application time of the bias voltage applied to the light receiving element is controlled according to the calculated accumulation time. .

According to a third aspect of the present invention for solving the above-mentioned problems of the conventional example, in an image sensor, a light amount detecting means for detecting a light amount emitted from a light source, and an illuminance is calculated from the detected light amount. Illuminance calculation means, storage time calculation means for calculating charge storage time in the light receiving element from the calculated illuminance and a preset appropriate light amount value,
Reset timing control means for controlling the reset timing of the reset switch for resetting the electric charge remaining in the light receiving element according to the calculated storage time.

According to a fourth aspect of the present invention for solving the above-mentioned problems of the conventional example, in the image sensor reading method, the amount of light emitted from the light source is detected, and the illuminance is calculated from the detected amount of light. Calculating the charge accumulation time in the light receiving element from the calculated illuminance and a preset appropriate light quantity value, and controlling the reset timing of a reset switch that resets the charges remaining in the light receiving element according to the calculated accumulation time. Is characterized by.

[0014]

According to the invention described in claim 1, the charge accumulation time in the light receiving element corresponding to the light quantity of the light source detected by the light quantity detecting means is calculated by the accumulation time calculating means, and the light receiving element is determined based on the accumulation time. Since it is an image sensor that controls the application time of the applied bias voltage, reading can be performed with an appropriate accumulation time that corresponds to the actual light intensity of the light source, and the sensor output is stable even if the light intensity of the light source changes significantly. Can be kept.

According to the second aspect of the invention, the charge accumulation time in the light receiving element corresponding to the detected light amount of the light source is calculated, and the application time of the bias voltage applied to the light receiving element is controlled based on the accumulation time. Since the image sensor reading method described above is used, the reading can be performed with an appropriate accumulation time corresponding to the actual light amount of the light source, and the sensor output can be stably maintained even when the light amount of the light source largely changes.

According to the third aspect of the invention, the charge accumulation time in the light receiving element corresponding to the light quantity of the light source detected by the light quantity detection means is calculated by the accumulation time calculation means, and the reset switch operation is performed based on the calculated accumulation time. Since the image sensor controls the reset timing, the reading can be performed with an appropriate accumulation time corresponding to the actual light amount of the light source, and the sensor output can be kept stable even if the light amount of the light source changes significantly.

According to the fourth aspect of the invention, the reading of the image sensor for calculating the charge accumulation time in the light receiving element corresponding to the detected light amount of the light source and controlling the reset timing of the reset switch based on the accumulated time. Since this method is used, the reading can be performed with an appropriate accumulation time corresponding to the actual light amount of the light source, and the sensor output can be kept stable even if the light amount of the light source changes significantly.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an equivalent circuit diagram of an image sensor according to an embodiment of the present invention. In the image sensor of the present embodiment, as shown in FIG. 1, the number of the light receiving elements 11 ″ of the photodiode P is one block, and the light receiving element array 11 is formed by N blocks. ″
The photodiodes P are connected to the drain electrodes of the charge transfer thin film transistors TT of the charge transfer unit 12, respectively. The source electrode of the charge transfer thin film transistor TT has a common signal line 14 via the matrix wiring 13.
And to the driving IC 15.

The gate electrode of the charge transfer thin film transistor TT is connected to a gate pulse shift register 16 for generating a gate pulse via a transfer gate signal line GT in block units.

Further, the image sensor of this embodiment is similar to that shown in FIG.
As shown in, the bias voltage VB is applied to the photodiode P.
The bias shift register 21 for applying is connected in block units, and the time for applying the bias voltage in each block is calculated from the amount of light detected by the light amount sensor 26.
Bias shift register control circuit 2 for controlling the bias voltage application time in the bias shift register 21
Two are provided. The light amount sensor 26 uses a photodiode as a light receiving element.

The bias shift register control circuit 22 includes an illuminance calculation circuit 23 for calculating the illuminance from the amount of light detected by the light amount sensor 26, and a bias for calculating the bias voltage application time based on the value from the illuminance calculation circuit 23. It comprises a voltage application time calculation circuit 24 and a shift register data creation circuit 25 which creates data relating to the bias voltage application time based on the value calculated by the bias voltage application time calculation circuit 24. Here, the illuminance calculation circuit 23
The bias voltage application time calculation circuit 24 is composed of an AD conversion circuit and a CPU, and the shift register data creation circuit 25 is composed of a logic circuit.

Before specifically explaining the bias shift register control circuit 22 which is a characteristic part of the image sensor of this embodiment, the control principle for controlling the bias voltage application time will be described. In the image sensor of this embodiment,
From FIG. 2 which shows the light source light amount and the accumulation time in the light receiving element with respect to the elapsed time, when the light source light amount L changes so as to increase with the elapsed time t, when the light source light amount L is low, the accumulation time ts is increased. It can be understood that the sensor output can be controlled to be constant by increasing the sensor output and decreasing the accumulation time ts to decrease the sensor output when the light source light amount L is large.

When the sensor sensitivity is S [V / 1x · sec], the illuminance is E [1x], and the storage time is ts [sec],
The sensor output Vo [V] is represented by the following formula. Vo = S × E × ts E × ts is the light quantity. Here, the sensor output Vo and the sensor sensitivity S that are desired to be kept constant are predetermined, and the illuminance E is always detected by the light amount sensor 26 and the illuminance calculation circuit 23. Therefore, the accumulation time ts is calculated by the following formula. Desired. ts = Vo / (S × E) If the bias voltage application time is controlled by the accumulation time ts calculated according to the above equation, a constant sensor output Vo can be obtained.

Next, the bias shift register control circuit 22 will be specifically described with reference to FIG. Figure 3
It is explanatory drawing which shows a bias voltage control process. As the light source 27, a cold cathode tube, EL (electroluminescence)
Any of a sheet, an LED (light emitting diode) array, and other planar light sources may be used.

The amount of light emitted from the light source 27 is read by the light amount sensor 26 of the photodiode, and this amount of light is converted into an electric signal by photoelectric conversion, and the illuminance calculation circuit 23 in the bias shift register control circuit 22 is read. Be transmitted to. The illuminance calculation circuit 23 calculates the actually measured illuminance Em based on the received electric signal and outputs the illuminance Em to the bias voltage application time calculation circuit 24. Measured illuminance Em
When the received electric signal is digitized by the AD conversion circuit, it becomes a light quantity value Lm at the light quantity sensor 26, and when this light quantity value Lm is divided by the actual irradiation time tm, the measured illuminance E
m can be calculated. That is, Em = Lm / tm.

The bias voltage application time calculation circuit 2
In 4, Vo (ideal sensor output) = S (sensor sensitivity)
An ideal proper light amount value Lo (=) obtained in advance by a calculation formula of × Eo (ideal illuminance) × tso (ideal storage time)
Eo × tso) and the actually measured illuminance Em given from the illuminance calculation circuit 23 are read, and an appropriate bias voltage application time (accumulation time ts) is obtained from the appropriate light amount value Lo and the actually measured illuminance Em.
) Is calculated. As a method of calculating the accumulation time ts, the accumulation time ts can be calculated by dividing the appropriate light amount value Lo by the actually measured illuminance Em. That is, ts = Lo / Em.

The calculated appropriate accumulation time ts is output to the shift register data creation circuit 25, and the bias voltage application is turned ON / OFF in the shift register data creation circuit 25.
Data for determining the OFF timing is created, the data is given to the bias shift register 21, and the bias voltage is applied from the bias shift register 21 to the photodiode P of the light receiving element for a specific time (accumulation time ts) according to the data. It is what is done.

The image sensor of this embodiment using the bias shift register control circuit 22 shown in FIG. 3 corresponds to the illuminance Em calculated by the illuminance calculation circuit 23 based on the light quantity detected by the light quantity sensor 26. Appropriate accumulation time t
Since s is calculated from the appropriate light quantity value Lo and the bias voltage application time is controlled by this accumulation time ts, even if the light quantity of the light source 27 changes significantly, the sensor output Vo
Can be held constant, and variations in the output of the image signal can be reduced. Further, since the accumulation time ts is obtained and the accumulation time ts is controlled while detecting the light quantity by the light quantity sensor 26, it is possible to read an image without slowing the reading speed of the image sensor. .

In the above embodiment, for example, when the light amount of the light source 27 is low, the actually measured illuminance Em obtained by the illuminance calculation circuit 23 becomes small, and the appropriate accumulation time ts for the appropriate light amount value Lo becomes long. Therefore, the bias voltage application time from the bias shift register 21 to the light receiving element is controlled to be long, and the sensor output Vo can be kept constant.

Next, an image sensor of another embodiment will be specifically described with reference to FIGS. 4 and 5. FIG. 4 is an equivalent circuit diagram of a one-dimensional image sensor of another embodiment,
FIG. 5 is an explanatory diagram showing a reset timing control process in the image sensor of FIG. It should be noted that portions having the same configurations as those of the image sensor of FIGS. 1 and 3 will be described with the same reference numerals.

In an image sensor of another embodiment, as shown in FIG. 4, the light receiving element 11 "of the photodiode P is n
The light receiving element array 11 is made up of N blocks, each of which is one block.
Is formed. The photodiode P of the light receiving element 11 ″ is connected to the drain electrode of the charge transfer thin film transistor TT of the charge transfer unit 12, and is also connected to the drain electrode of the reset thin film transistor TR. The source electrode of TR is grounded, and the source electrode of the charge transfer thin film transistor TT is connected to the common signal line 14 via the matrix wiring 13 and further connected to the driving IC 15.

Further, the gate electrode of the charge transfer thin film transistor TT is connected to the gate pulse shift register 16 for generating a gate pulse via the transfer gate signal line GT in block units, and the gate electrode of the reset thin film transistor TR is also blocked. The unit is connected to the gate pulse shift register 16 via the reset gate signal line GR.

Further, the gate pulse shift register 16
A gate pulse shift register control circuit 22 'is connected to the gate pulse shift register control circuit 22', and controls a pulse output from the gate pulse shift register 16 to the gate electrode of the reset thin film transistor TR (a pulse at which resetting is performed). . A light amount sensor 26 for detecting the light amount from the light source 27 is connected to the gate pulse shift register control circuit 22 '.

The image sensor of FIGS. 4 and 5 has a light quantity sensor 26 as compared with the image sensors of FIGS.
The procedure is the same until the amount of light from the light source 27 is detected and the illuminance calculation circuit 23 obtains the illuminance Em to calculate the charge storage time ts in the light receiving element, but the subsequent processing is different.

Comparing the circuit shown in FIG. 3 with the circuit shown in FIG. 5, in FIG. 4, instead of the bias shift register control circuit 22, the gate pulse shift register control circuit 22 ′ has a bias voltage application time calculation circuit. A storage time calculation circuit 24 'is provided in place of 24, and the shift register data creation circuit 25' creates control data in the gate pulse shift register 16, and therefore the shift register data creation circuit 25 'is provided. The gate pulse shift register 16 is connected. However, the bias voltage application time calculation circuit 24 and the storage time calculation circuit 24 'have the same configuration and perform the same processing.

When the calculated storage time ts is given to the shift register data creation circuit 25 ', the shift register data creation circuit 25' determines the reset thin film transistor in the gate pulse shift register 16 based on the storage time ts. Data for controlling the timing of turning on / off the TR is created, and the data is output to the gate pulse shift register 16.

Here, the relationship between the accumulation time ts and the timing for turning on / off the reset thin film transistor TR will be described. Generally, the operation of the reset thin film transistor TR is to reset the charge remaining in the light receiving element after the charge transfer thin film transistor TT is turned on to transfer the charge accumulated in the light receiving element to the matrix wiring 13. Accumulation of charges in the light receiving element starts from the time when the reset thin film transistor TR is turned off, and ends when the charge transfer thin film transistor TT is turned on. Therefore, the reset timing of the reset thin film transistor TR is set at an arbitrary timing. The storage time can be controlled by setting to.

Therefore, in the shift register data generation circuit 25 ', for example, the charge transfer thin film transistor TT is used.
Is fixed, and the reset thin film transistor TR is turned on / off so that the time from the time when the reset thin film transistor TR is turned off to the time when the charge transfer thin film transistor TT is turned on is equal to the accumulation time ts.
Create data that controls the timing of off. Then, according to the data, the gate pulse shift register 1
6, the reset on / off timing is controlled, and an ideal charge accumulation time for keeping the sensor output Vo constant is set. Therefore, FIG. 4 and FIG.
This image sensor can also obtain the same effect as that of the image sensor of FIGS.

Although the one-dimensional image sensor has been described in the present embodiment and the other embodiments, it can be applied to a two-dimensional image sensor as shown in FIG. FIG. 6 shows a two-dimensional image sensor and a light amount sensor 2 of this embodiment.
6 is an equivalent circuit diagram in which 6 and a shift register control circuit for bias 22 are added.

In particular, since the two-dimensional image sensor scans a plurality of lines as compared with the one-dimensional image sensor, the charge accumulation time in the light receiving element tends to be too long, and the two-dimensional image sensor shown in FIG. As a result, the reading method for controlling the accumulation time shown in FIG. 3 has an effect of effectively suppressing the saturation of the sensor output. Further, naturally, the effect that the sensor output described in FIG. 3 can be kept constant can be realized.

It is also possible to apply another embodiment for controlling the reset timing described in FIGS. 4 and 5 to a two-dimensional image sensor in the same manner as described above, and the same effect as described above can be obtained.

When the charge storage time of the light receiving element becomes long, the dark current noise component also increases and is saturated before the gate of the charge transfer thin film transistor TT is turned on, making it impossible to read the document. Therefore, by controlling the accumulation time as in the image sensor reading method of the present embodiment,
Unreadable reading can be prevented and dark output can be suppressed to a low level to secure an effective output range (dynamic range) of the image sensor. In this case, the sensor sensitivity has a characteristic that it is directly proportional to the accumulation time as shown in the explanatory view showing the dependency of the sensor sensitivity on the accumulation time in FIG. 7, so that the sensor sensitivity can be controlled from about 1% to 100%. .

[0043]

According to the first aspect of the invention, the charge accumulation time in the light receiving element corresponding to the light quantity of the light source detected by the light quantity detection means is calculated by the accumulation time calculation means, and the light reception is performed based on the accumulation time. Since it is an image sensor that controls the application time of the bias voltage applied to the element, it is possible to read with an appropriate accumulation time that corresponds to the actual light intensity of the light source, and even if the light intensity of the light source changes significantly, the sensor output It has the effect of keeping it stable.

According to the second aspect of the invention, the charge accumulation time in the light receiving element corresponding to the detected light amount of the light source is calculated, and the application time of the bias voltage applied to the light receiving element is controlled based on the accumulation time. Since the image sensor reading method is used, reading can be performed with an appropriate accumulation time corresponding to the actual light amount of the light source, and the sensor output can be kept stable even if the light amount of the light source changes significantly. is there.

According to the third aspect of the present invention, the charge accumulation time in the light receiving element corresponding to the light quantity of the light source detected by the light quantity detection means is calculated by the accumulation time calculation means, and the reset switch of the reset switch is calculated based on the calculated accumulation time. Since it is an image sensor that controls the reset timing, it is possible to read with an appropriate accumulation time that corresponds to the actual light intensity of the light source, and the sensor output can be kept stable even if the light intensity of the light source changes significantly. There is.

According to the fourth aspect of the invention, the reading of the image sensor for calculating the charge accumulation time in the light receiving element corresponding to the detected light amount of the light source and controlling the reset timing of the reset switch based on the accumulated time. Since this method is used, reading can be performed with an appropriate accumulation time corresponding to the actual light amount of the light source, and there is an effect that the sensor output can be kept stable even if the light amount of the light source changes significantly.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram of a one-dimensional image sensor according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a light source light amount and an accumulation time with respect to an elapsed time.

FIG. 3 is an explanatory diagram showing a bias voltage control process.

FIG. 4 is an equivalent circuit diagram of a one-dimensional image sensor of another embodiment.

5 is an explanatory diagram showing a reset timing control process in the image sensor of FIG.

FIG. 6 is an equivalent circuit diagram showing an application example to a two-dimensional image sensor.

FIG. 7 is an explanatory diagram showing accumulation time dependency of sensor sensitivity.

FIG. 8 is an explanatory diagram showing a light amount of a light source with respect to an elapsed time from turning on the light source.

FIG. 9 is an explanatory diagram showing a relationship between sensor output and light amount of a conventional light source.

[Explanation of symbols]

11 ... Light receiving element array, 12 ... Charge transfer section array,
13 ... Matrix wiring, 14 ... Common signal line, 15 ...
Driving IC, 16 ... Shift register for gate pulse,
21 ... Bias shift register, 22 ... Bias shift register control circuit, 22 '... Gate pulse shift register control circuit, 23 ... Illuminance calculation circuit, 2
4 ... Bias voltage application time calculation circuit, 24 '... Accumulation time calculation circuit, 25, 25' ... Shift register data creation circuit, 26 ... Light intensity sensor, 27 ... Light source

Claims (4)

[Claims] 1. A light amount detecting means for detecting a light amount emitted from a light source, an illuminance calculating means for calculating an illuminance from the detected light amount, and a light receiving element from the calculated illuminance and a preset appropriate light amount value. 2. An image sensor, comprising: an accumulation time calculating means for calculating an accumulation time of charges in 1); and a bias voltage control means for controlling an application time of a bias voltage applied to the light receiving element according to the calculated accumulation time. 2. The amount of light emitted from a light source is detected, the illuminance is calculated from the detected light amount, and the charge accumulation time in a light receiving element is calculated from the calculated illuminance and a preset appropriate light amount value, A method for reading an image sensor, comprising controlling an application time of a bias voltage applied to the light receiving element according to the calculated storage time. 3. A light amount detecting means for detecting a light amount emitted from a light source, an illuminance calculating means for calculating an illuminance from the detected light amount, and a light receiving element based on the calculated illuminance and a preset appropriate light amount value. And a reset timing control means for controlling the reset timing of a reset switch for resetting the charges remaining in the light receiving element according to the calculated storage time. Image sensor. 4. A light amount emitted from a light source is detected, an illuminance is calculated from the detected light amount, and a charge accumulation time in a light receiving element is calculated from the calculated illuminance and a preset appropriate light amount value, A method of reading an image sensor, comprising controlling a reset timing of a reset switch that resets charges remaining in the light receiving element according to the calculated storage time.