JPS61167267A - Image sensor - Google Patents

Abstract

PURPOSE:To prevent omission of reading and duplicate reading effectively by setting a white threshold width as the length of opening of a comblike electrode corresponding to the white threshold width when it is deviated to the black side by a preset correction value. CONSTITUTION:In an coplanar type image sensor, for instance, the width W and slit width l of an opening 2 are set to 10mum respectively and reading of picture information of 4-line pair/mm is performed. When the white and black threshold level SL was determined, supposing that the time required to change from black to white is t1, the time required to change from white to black is t2, and the time required to change next from black to white is t3 when reading 4 line pair/mm at 5ms/line equivalent, the white threshold width TW becomes t2-t1, and the black threshold width becomes t3-t2. When a light response output of the image sensor is binary-coded by the level SL, the condi tion for eliminating omission of reading and duplicate reading wherever is the timing of reading of the picture information is TW=TB=5ms.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image sensor, and more particularly to an improvement of a light-receiving aperture in a coplanar image sensor having comb-shaped electrodes.

In general, when the original image information obtained by optically scanning the document surface is read dot by dot at the same magnification using a photoconductive image sensor element, double reading occurs if the aperture length of the light receiving aperture is large. In addition, if the aperture length is small, there is a problem in that thin lines continue to fall, so it is necessary to set the aperture length optimally.

Conventionally, the optimum value of the aperture length in an image sensor having a rectangular aperture is described in the Journal of the Institute of Electronics and Communication Engineers ``81/
7 VOL, JE) I-CNo, paper r in 7
In "contact image sensor using CdS photoconductive film", rA in wave phase IE80-72 of Institute of Electronics and Communication Engineers
4-format high-density image sensor''. 'However, this is only applicable to determining the aperture length in the case of an image sensor that has a rectangular aperture, and cannot be directly applied to a coplanar image sensor that has comb-shaped electrodes. It has become.

The present invention has been made in consideration of the above points, and particularly relates to a coplanar image sensor having a comb-like electrode.
An object of the present invention is to provide an image sensor in which the aperture length of its electrodes is determined so as not to cause double reading or failure to read thin lines.

1. In order to achieve the object, the present invention shifts the white threshold width when binarizing the image sensor output signal to the black side by a preset correction value, and corresponds to the shifted white threshold width. The opening length of the comb-shaped electrode is set to be the same.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows the shape of a comb-shaped electrode 1 in a coplanar image sensor, which allows image information to be read at 4 line bears/mm. Note that here, for example, the width W of the comb-like electrode 1 and the width Q of the ribs 1 to the opening 2 are each set to 10 μm. Therefore, the opening width W is 90 μm.

In such an image sensor, it is necessary to have a large aperture width in the sub-scanning direction so that the photoconductive sensor element output can be large, but if the aperture width is made too large, double reading may occur. If the width of the opening is too small, the reading of fine lines will occur.

Currently, there is an image sensor with a comb-shaped electrode as shown in Fig. 1, and the aperture length is set as a parameter of 20~
Inspection of the sensor output current characteristics when changing the current within a range of 120 μm and irradiating light information such that the part corresponding to white in Figure 2 becomes level "1" and the part corresponding to black becomes level re Ou. When taken, it becomes as shown in Fig. 3 or 4. Here, FIGS. 3 and 4 show the sensor output current characteristics when the sensor element is formed using a-Si by the plasma CVD method under different film forming conditions.

In addition, as shown in Figure 6, the black and white threshold level S
When deciding L, 4 line bear/m rn 5mS/
When reading by line equivalent, the time to change from black to white is tl, then the time to change from white to black is t2. Next, if the time for changing from black to white is t3, the white threshold width (time width that is read as white) Tw is Tw = t2 ~ t
1, and the black threshold width (time width that is read as black) T is TB=t3 t2. In the figure, ML
indicates the white saturation level.

Here, when the photoresponse output of the image sensor shown in FIG. The conditions to prevent reading are Tw = TB = 5mS ・
...(1).

At that time, in the actual reading of image information, it is expected that misreading of black will be more of a problem than double reading of black, so by inserting a slight correction value ε into equation (1), Tw + t = TB −t==5ms=(2) is a condition that provides a practical optimum threshold width. That is, when setting T W + TB to 5 mS, it is unavoidable that an error occurs, and if an error occurs anyway, the black threshold width Tw is shifted by E from the beginning.

Further, normally, an MTF corresponding to the resolution in the sub-scanning direction when reading a document image by an image sensor is required to be 60% or more. Note that the MTF takes into consideration the sub-scanning feed of the original, and as shown in FIG. 5, MTF = MTF =
((Vmax - Vmin) / (Vmax - Vm
in)) x 100 (%).

Therefore, we determined the aperture length so that the image sensor with the comb-shaped electrode shown in Fig. 1 would not fail to read the black information of 4 lines/mm, and would minimize double reading. and the optimum value Do of the opening length
From the characteristics shown in FIG. 7, 75 μm<Do≦80pm −(3).

As described above, in the image sensor according to the present invention, in a coplanar image sensor having comb-like electrodes, the white threshold width when binarizing the image sensor output signal is blackened by a preset correction value. The opening length of the comb-shaped electrode corresponds to the white threshold width when shifted to the side, and has the excellent advantage of effectively preventing burn-out of fine lines and double reading. ing.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a coplanar image sensor having comb-shaped electrodes according to the present invention, FIG. 2 is a diagram showing a pattern of light information irradiated onto the image sensor, and FIGS. 3 and 4. are diagrams showing the characteristics of the relative value of the image sensor output current when the aperture length is taken as a parameter, Figure 5 is a diagram showing the output characteristics of the image sensor, Figure 6 is a diagram showing the photoresponse output characteristics of the image sensor, FIG. 7 is a diagram showing the characteristics of the white threshold width with respect to the aperture length of the image sensor. 1...Comb-shaped electrode 2...Aperture D...Open [1 length W...Aperture width Tw...White threshold width T
...Black threshold width

Claims (1)

[Claims] Corresponds to the white threshold width when shifting the white threshold width when converting the image sensor output signal into a binary value to the black side by a preset correction value in a coplanar image sensor with a comb-shaped electrode. An image sensor characterized in that the aperture length of the comb-shaped electrode is set.