JP2688922B2 - Image sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor for reading image information on a document by arranging a single or a plurality of sensors of the same size as a transmission document for facsimile, for example. .

[Conventional technology]

In recent years, technological advances in photoelectric conversion devices such as facsimiles and optical character readers (OCRs) have made remarkable progress. ing.

FIG. 7 is a sectional view showing a conventional image sensor shown in the catalog of "Mitsubishi close contact image sensor" issued by Mitsubishi Electric Corporation in June 1987. (1) in the figure is For example, a light-emitting element such as an LED, (2) is a light-receiving element, (3) is a light-receiving element (2), and is a rod lens array for performing one-to-one equirectangular imaging, and (4) is a light-emitting element. (1) and a light transmitting plate made of, for example, glass, which is located above the rod lens array (3), (5) is an original moving on the light transmitting plate (4), and 5a is its reading position,
(6) is a platen roller for conveying the original (5), (10)
Is a frame for fixing the light emitting element substrate (7) to the light receiving element substrate (8), the rod lens array (3), the light transmitting plate (4), the drive circuit (9) and the like.

Next, the operation will be described. The document (5) conveyed by the platen roller (6) moves on the light transmitting plate (4). At this time, the light emitted from the light emitting element (1) produces reflected light at the reading position 5a of the original (5), and the image thereof becomes an image of an erecting equal size by the rod lens array (3). ) Is received and is converted into an electric signal by the drive circuit (9).

Then, the document (5) is read by continuously feeding the document (5). Next, these electrical operations will be described with reference to the block diagram of FIG. 8 and the timing diagram of FIG. In the figure, 5 V is applied between VLED and GLED of the light emitting diode which becomes the light emitting element (1) to cause the light emitting element (1) to emit light. Due to this light emission, the reflected light of the Harabashi (5) is received by the plurality of light receiving elements (2) arranged on the light receiving element substrate (8), and the analog switches connected to each are sequentially driven by the shift register. By taking out the electric charges received by the light receiving elements (2) and taking out the electric charges of all the light receiving elements (2), a one-line original reading output signal is obtained. Here, SI is a data signal to be transferred to the first bit of the shift register, which is a reading start signal for one line, CLOOK is a transfer timing signal of the shift register, and SIG is an original reading output signal. Further, AMP indicates an amplifier circuit for the output signal, and VDD (+ 5V), Vss (-12V), etc. indicate the power source of the drive circuit. Further, FIG. 6 shows a temperature characteristic curve of the light receiving element (2) and shows that the output level of the original reading output signal fluctuates due to the temperature rise.

[Problems to be solved by the invention]

Since the conventional image sensor is configured as described above, the original reading output signal fluctuates due to temperature changes, and a large amount of current is consumed to cause all the LEDs that are light emitting elements to emit light. There were problems such as the short life of the LED.

The present invention has been made in order to solve the above problems, and further reduces the fluctuation of the document reading output signal due to temperature change, reduces the current consumption of the light emitting element, and extends the life of the LED. It is an object of the present invention to obtain an image sensor that can obtain higher light receiving sensitivity.

[Means for Solving the Problems] In an image sensor according to the present invention, a plurality of light emitting elements are arranged linearly, and a light emitting element group alternately connected to the first and second terminals, and the light emitting element. The light from each light emitting element of the group is reflected by the original and provided with a rod lens array that focuses the reflected light respectively and each light emitting element, and the output level increases as the temperature rises. A light receiving element group having a plurality of light receiving elements, which receives the light focused by the rod lens array, a shift register for taking out electric charges received by each light receiving element of the light receiving element group, and the first and second Pulses with opposite ON / OFF pulses are alternately applied to the terminals of, and the applied pulse width is narrowed when the temperature rises and the applied pulse width is lowered when the temperature is lowered due to temperature fluctuation. The pulse drive means for compensating for the temperature fluctuation of the light receiving element by widely changing the pulse width, and the current applying means for supplying the current according to the pulse width are provided.

[Action]

In the image sensor according to the present invention, the first terminal and the second terminal, which are alternately connected to the linearly arranged light receiving elements, are alternately applied with on / off conflicting pulses, and due to temperature fluctuation, The pulse width of this pulse is narrowed when the temperature is high, and is widened when the temperature is low, so that the temperature fluctuation of the light receiving element is compensated.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. The sectional view and the operation of the image sensor are the same as those of the conventional one, and the description thereof will be omitted. Now, what is different from the conventional one is, as shown in the block diagram of FIG. 1, the LEDs which are the light emitting elements (1) in the light emitting element array are alternately divided into two groups and connected to the common electrodes 1a and 1b, LED as shown
Is pulse-driven to alternately emit the LEDs connected to the common electrodes 1a and 1b.

The present inventor, for the purpose of investigating the lifespan of an LED pulse drive, uses the duty of the pulse drive and the LED applied current as parameters to change the light emission change rate from the initial after 5 hours of light emission for 5 hours.
LED was used within%, and the relationship was experimentally determined. The curve diagram shown in Fig. 3 is that, and it depends on the thermal time constant of the LED, the thermal time constant of the LED mounting board, etc.
The tendency was similar to that in FIG.

Further, when the LED was made to emit light by these pulse drive and applied current, the light receiving sensitivity of the light receiving element (2) was examined. This is what is shown in FIG. 4, and in the range examined by the present inventor, the pulse duty is set to about 50% and the applied current is increased as much as possible to increase the light emission amount of the LED and the light receiving sensitivity is further increased (accumulation). The saturated output level is reached even if the time is short). According to the experimental results of FIG. 3 and FIG.
Conventionally, one LED consumes 20mA, and the light emitting element array in which 20 LEDs are arranged consumes 400mA.
By alternating pulse drive, even if each consumes 30mA
The total current consumption is 300mA, and the sensitivity of the light receiving element is also increased. If the photosensitivity is the same as before, the total current consumption can be further reduced and the LED life can be extended.

Further, as shown in FIG. 5, by increasing the pulse width when the temperature is low and shortening the pulse width when the temperature is high to change the amount of light emission, the sensitivity of the light receiving element is made worse at high temperatures. It is possible to eliminate the temperature characteristic shown in FIG.

Further, the light emitting element is driven by pulse and the pulse width is changed, so that the light receiving sensitivity can be easily changed arbitrarily.

In the above embodiment, the case where the light receiving element (1) is an LED is shown, but other light receiving elements may be used.
Further, in the above embodiment, the case where the light emitting elements of the light emitting element array are divided into two groups and alternately pulse-driven has been described. However, in order to reduce current consumption, pulse driving may be further divided into a plurality of groups. The duty is not limited, either.

〔The invention's effect〕

As described above, according to the present invention, it is possible to reduce the total current consumption of the light-emitting element and prolong the life of the light-receiving element, and at the same time, to increase the temperature due to the change of the outside air temperature and the operation of the incorporated device. On the other hand, there is an effect that the temperature variation of the light receiving element, whose output increases as the temperature rises, is compensated on the side of the light emitting element, and it becomes possible to read the document with high accuracy. Further, since the pulses are alternately applied to the light receiving elements, the unevenness of light emission is reduced and the effect of suppressing the unevenness of reading the original is also obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of an image sensor according to an embodiment of the present invention, FIG. 2 is a drive timing diagram of the light emitting element of FIG. 1, and FIG. Point), FIG. 4 is a diagram showing the light receiving sensitivity by pulse driving, FIG. 5 is a diagram showing that temperature fluctuation is eliminated by changing the pulse width, and FIG. 6 is a temperature characteristic diagram of the light receiving element. FIG. 7 FIG. 8 FIG. 9 are a sectional view / block diagram and a timing diagram showing a conventional image sensor. Reference numeral (1) is a light emitting element, (1a) and (1b) are common electrodes, (2) is a light receiving element, (3) is a rod lens array, and (9) is a drive circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A light emitting element group in which a plurality of light emitting elements are linearly arranged and alternately connected to first and second terminals, and light from each light emitting element of the light emitting element group is reflected by an original. The rod lens array includes a rod lens array that focuses the reflected light, and a plurality of light receiving elements that are provided corresponding to the respective light emitting elements and whose output level increases as the temperature rises. Light receiving element group for receiving the light focused by the light receiving element, a shift register for taking out the electric charge received by each light receiving element of the light receiving element group, and pulses which are alternately turned on and off at the first and second terminals. In addition to applying the pulse width, when the temperature rises, the applied pulse width is narrowed when the temperature rises, and when the temperature drops, the pulse width applied is widened to compensate for the temperature fluctuation of the light receiving element. Image sensor characterized by comprising that the pulse driving means and a current applying means for flowing a current corresponding to the pulse width.