JP2591346B2 - Image reading device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document reading apparatus used in a facsimile machine or the like, and more particularly to a document reading apparatus mainly used for the difference in the length of a wiring conductor connecting each photoelectric conversion element and a switch element corresponding to the photoelectric conversion element. The present invention relates to a document reading apparatus in which the variation of an output signal depending on the original is reduced to a level that is completely or negligible.

[0002]

2. Description of the Related Art Generally, a document reading apparatus includes a large number of photoelectric conversion elements arranged in a predetermined pattern on an insulating substrate, and performs switching scanning of these photoelectric conversion elements to correspond to the amount of light received by each photoelectric conversion element. In order to extract a signal to be converted, a switching circuit including the same number of switch elements as the photoelectric conversion elements is provided on the same substrate as the photoelectric conversion elements or on the outside.

Here, the length of the photoelectric conversion element array is configured to be the same size as the original to be read.

In such an original reading apparatus, since an original is read by one-to-one image formation using an optical system such as an optical fiber array or a lens array, it is possible to shorten the image forming optical path length. Thus, the size of the document reading apparatus can be significantly reduced.

FIG. 3 is a circuit diagram of a conventional document reading apparatus, wherein P1, P2, P3... PN are photoelectric conversion elements formed of a photoconductive thin film, and equivalently, a photodiode P1.
D and a capacitor CD.

.. QN are MOs for switching the photoelectric conversion elements P1 to PN, respectively.
The S transistor 1 is a shift register for scanning the MOS transistors Q1 to QN.
The PN and the MOS transistors Q1, Q2, Q3... QN are connected via wiring conductors W1 to WN, respectively.

A switching circuit 2 constituted by the shift register 1 and MOS transistors Q1 to QN
Are integrated on a semiconductor substrate.

3 is an output signal line, 4 is an output terminal, 5
Is a load resistance, and 6 is a bias power supply.

FIGS. 4 and 5 are plan views showing an example of a specific structure of the document reading apparatus shown in FIG.
FIG. 3 is a sectional view taken along line III.

The photoelectric conversion elements P1 to PN are arranged above and below the photoconductive thin film 7 with electrodes S1 to S divided by a conductive thin film.
It is formed on an insulating substrate 9 in a manner sandwiched between N and a continuous electrode 8 made of a transparent conductive thin film.

The divided electrodes S1 to SN are attached on a substrate 9, and the wiring conductors W
1 to WN are extended and led out on the substrate 9.

Switching circuit 2 of semiconductor integrated circuit configuration
Are fixed on the substrate 9, and the pads thereof are electrically connected to the ends of the wiring conductors W1 to WN by connection lines B1 to BN.

In the above arrangement, when the original image is formed on the photoelectric conversion elements P1 to PN by the optical system, the photoelectric conversion elements P1 to PN output a photocurrent corresponding to the intensity of the light received by the photodiode PD. , And the electric charge is accumulated in the capacitor CD.
The signal is transmitted to the output signal line 3 by sequentially turning on the S transistors Q1 to QN, and is taken out from the output terminal 4 as a video signal.

FIG. 6 shows an equivalent circuit for one photoelectric conversion element. One of the photoelectric conversion elements P1 to PN corresponds to a current source 11 and MOS transistors Q1 to Q1.
The switch element 12 corresponds to one of N 1.

The capacitor 13 is connected between the photoelectric conversion elements P1 to PN to M
The stray capacitance of the wiring between the OS transistors Q1 to QN and M
The capacitance 14 is a combined capacitance of the input capacitances of the OS transistors Q1 to QN and the capacitance 14 is a combined capacitance of the output capacitance of the MOS transistors Q1 to QN and the floating capacitance of the output signal line 3.

When light enters the photoelectric conversion element, a current flows through the current source 11 and charges are accumulated in the capacitor 13. Here, when the switch 12 is closed, the electric charge accumulated in the capacitor 13 is discharged through the capacitor 14 and the resistor 5, and the discharge current is detected at the output terminal 4.

[0017]

In FIG. 4, the photoelectric conversion elements P1 to PN and the MOS transistor Q are shown.
Wiring conductors W1 to W connected between 1 to QN, respectively.
6 shows the case where the lengths of N are equal. In this case, since the stray capacitances of the respective wiring conductors W1 to WN are substantially equal, FIG.
Is considered to be almost constant.

However, in an actual device, as shown in FIG. 7, for example, the wiring conductors W1 to WN are often extended to the side of the switching circuit 2 constituted by a semiconductor integrated circuit. Conductor W1
... WN are formed on the substrate 9 as having different lengths.

In this case, the stray capacitance of each of the wiring conductors W1 to WN differs, and the capacitance 13 shown in FIG. 6 differs depending on each of the photoelectric conversion elements P1 to PN. There is a drawback that the variation is determined by the CR time constant.

Accordingly, the present invention provides a document reading apparatus in which the variation of the output signal mainly depending on the difference in the length of each wiring conductor from the photoelectric conversion element to the switch element is reduced to a level that is negligible or negligible. The purpose is to:

[0021]

In order to achieve the above-mentioned object, the present invention provides a plurality of photoelectric conversion elements and a plurality of switch elements corresponding to the photoelectric conversion elements on the same substrate. In a document reading apparatus, a photoelectric conversion element and a switch element corresponding to the photoelectric conversion element are connected via a wiring conductor, and a signal corresponding to the amount of light received by each photoelectric conversion element is taken out via the wiring conductor. Among the wiring conductors, the stray capacitance of the wiring conductor and the wiring capacitance of other wiring conductors other than at least those having the largest combined capacitance of the stray capacitance of the wiring conductor and the input capacitance of the switch element to which the wiring conductor is connected A capacitance element determined in accordance with a combined capacitance of the input capacitance of the switch element to which the conductor is connected, and a switch element to which the stray capacitance of the wiring conductor and the wiring conductor are connected; Characterized in that each composite capacitance of the input capacitance is set to be equal to each other.

In the present invention, the stray capacitance of the wiring conductor and the input capacitance of the switch element to which the wiring conductor is connected, among the wiring conductors connecting each photoelectric conversion element and the switch element corresponding to the photoelectric conversion element. Capacitance elements determined in accordance with the combined capacitance of the stray capacitance of the wiring conductor and the input capacitance of the switch element to which the wiring conductor is connected to other wiring conductors except for at least the one with the largest combined capacitance. And the combined capacitance of the stray capacitance of each wiring conductor and the input capacitance of the switch element to which the wiring conductor is connected is made equal to each other, thereby minimizing the variation of the output signal to a negligible or negligible level. .

[0023]

Embodiments of the present invention will be described below in detail.

FIGS. 1 and 2 show an embodiment of a document reading apparatus according to the present invention, with circuit diagrams corresponding to FIGS. 3 and 6, respectively.

In this embodiment, the wiring conductor W in the switching circuit 2 constituted by a semiconductor integrated circuit is provided.
Compensating capacitive elements C1 to CN are connected in parallel to 1 to WN, respectively.

Here, the compensation capacitive elements C1 to CN
Is the capacitance 13 shown in FIG. 2, that is, the stray capacitance of the wiring from the current source 11 (photoelectric conversion elements P1 to PN) to the switching element 12 (MOS transistors Q1 to QN) and the switching element 12 (MOS transistors Q1 to QN). Has a capacitance value individually selected such that a combined capacitance with the input capacitance of the first and second input capacitors becomes constant.

These capacitive elements C1 to CN have a diffusion capacity by a PN junction, a capacity by a MOS structure, a capacity generated by interposing a dielectric between metal thin films, and the like.
It can be formed simultaneously with the formation of N.

In FIG. 2, this compensating capacitance element is generally shown as CK. In FIG. 2, the combined capacitance of the capacitance 13 and the capacitance of this compensating capacitance element CK is:
Each compensating capacitive element CK is selected so as to be substantially equal to each photoelectric conversion element.

In FIG. 1, each of the wiring conductors W1 to W1
The compensation capacitance elements C1 to CN are respectively connected to WN. However, in correspondence with all the wiring conductors W1 to WN, the compensation capacitance elements C1 to CN are not connected and the respective wiring conductors W1 to CN are connected. Among the wiring conductors WN, the stray capacitance of the wiring conductor is added to other wiring conductors except at least the combined capacitance of the stray capacitance of the wiring conductor and the input capacitance of the MOS transistors Q1 to QN to which the wiring conductor is connected. And the capacitance elements determined according to the combined capacitance of the input capacitances of the MOS transistors Q1 to QN to which the wiring conductors are connected, whereby the floating capacitance of each of the wiring conductors W1 to WN and the wiring conductor W1 are connected. To WN are connected to MOS transistors Q1 to QN
So that each combined capacitance with the input capacitance is equal.

For example, no compensating capacitive element is provided for the longest wiring conductor having the largest stray capacitance among the wiring conductors W1 to WN, and only the compensating capacitive element is provided for the short wiring conductor having a smaller stray capacitance. Configure to connect.

[0031]

As described above, according to the present invention,
Individually corresponding to each combined capacitance so that the combined capacitance of the stray capacitance of the wiring conductor connecting each photoelectric conversion element and the switch element corresponding to the photoelectric conversion element and the input capacitance of each switch element is equal. The capacitance element selected in (2) is connected to other wiring conductors except at least those having the largest combined capacitance of the stray capacitance of the wiring conductor and the input capacitance of the switch element to which the wiring conductor is connected. With such a configuration, there is an effect that the variation of the output signal mainly depending on the difference in the length of each wiring conductor from the photoelectric conversion element to the switch element can be reduced to a negligible or negligible level.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a document reading apparatus according to the present invention.

FIG. 2 is an equivalent circuit diagram of a reading circuit of the document reading apparatus shown in FIG.

FIG. 3 is a circuit diagram showing a conventional document reading apparatus.

FIG. 4 is a plan view of an example of a specific structure of the document reading apparatus shown in FIG. 3;

FIG. 5 is a sectional view taken along line III-III of the original reading apparatus shown in FIG. 4;

6 is an equivalent circuit diagram of a reading circuit of the document reading device shown in FIG.

FIG. 7 is a diagram for explaining a problem of the conventional device, and is a plan view showing an arrangement of wiring conductors.

[Explanation of symbols]

P1 to PN: photoelectric conversion elements, S1 to SN: divided electrodes, Q1 to QN: MOS transistors, W1 to WN: wiring conductors, C1 to CN: compensating capacitance elements, 1: shift registers, 2 switching circuits, DESCRIPTION OF SYMBOLS 3 ... Signal line, 4 ... Output terminal, 5 ... Load resistance, 6 ... Bias power supply, 7 ... Photoconductive thin film, 8 ... Continuous electrode by transparent conductive thin film, 9 ... Insulating substrate, 11 ... Current source, 12 ... Switch element, 13, 14
…capacity

Claims (1)

(57) [Claims] 1. A plurality of photoelectric conversion elements and a plurality of switch elements corresponding to the photoelectric conversion elements are provided on the same substrate, and each photoelectric conversion element and a switch element corresponding to the photoelectric conversion element are respectively provided. In a document reading apparatus connected via a wiring conductor and taking out each signal corresponding to the amount of light received by each photoelectric conversion element through the wiring conductor, the stray capacitance of the wiring conductor and the wiring conductor in the wiring conductor Corresponds to the combined capacitance of the stray capacitance of the wiring conductor and the input capacitance of the switch element to which the wiring conductor is connected to other wiring conductors except for at least the one with the largest combined capacitance with the input capacitance of the switch element to which the wiring conductor is connected. And the combined capacitance of the stray capacitance of the wiring conductor and the input capacitance of the switch element to which the wiring conductor is connected is made equal to each other. Document reading apparatus according to claim and.