JPS59143465A - Original reader - Google Patents

Abstract

PURPOSE:To reduce the capacity of a reading signal line and to read out an original at a high speed by dividing the signal line into plural signal lines and connecting the 2nd switching means extracting respective photoelectric conversion outputs in accordance with the divided signal lines. CONSTITUTION:Plural photoelectric converting elements 1a-1i each of which consists of a photodiode PD and a capacitor CD are formed on a board as a photoconductive thin film and photoelectric conversion outputs by respective elements 1a-1i are switched so as to be controlled by MOS transistors (TRs) 5a-5i, the 1st switching elements. Adjacent output electrodes of the TRs 5a- 5i are connected in common and the TRs 5a-5i are divided into blocks 5a- 5c, 5d-5f, 5g-5i. Respective parallel output lines of a shift register 6 are connected to the input electrodes of the TRs 5a-5i and a signal line 8 is connected to respective blocks through the 2nd switching elements 9A-9C. The elements 9A-9C are controlled by gates 20A-20C inputting the outputs of the register 6. Consequently, the original can be read out at a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a document reading device used in facsimiles, etc., and in particular to a document reading device using a MOS photodiode array or CC
The present invention relates to a contact type document reading device that has been recently developed in contrast to an IC type document reading device such as a D image sensor.

In general, a contact type original reading device is constructed by forming a plurality of photoelectric conversion elements on an insulating substrate, and providing a circuit for switching and scanning the elements on the same substrate or externally, and photoelectric conversion elements. The length of the conversion element array is the same size as the original, and the optical
Since the original is read by one-to-one imaging using an optical system such as a fiber play or lens array, it is possible to shorten the imaging optical path length and achieve a significant downsizing of the original reading device. It is something.

Figure 1 shows an equivalent circuit (a) of a conventional contact type document reading device.
and its schematic configuration is shown in the same figure (b), and A- in figure (b).
A sectional view taken along line A' is shown in (C).

In the figure (a), numeral 1 denotes a photoelectric conversion element formed of a photoconductive thin film, and isometrically constituted by a photodiode PD and a capacitor CD. 5 is a MOS transistor for switching the photoelectric conversion element, 6 is M
OS) shift register for scanning transistor 5,
8 is a signal line, 10 is a bias power supply, and 12 is an amplifier.

゛ ~ , - ゛ ・National old (su(0n): At %-V%, the photoelectric conversion element 1 has a photoconductive thin film 3 divided into an electrode 2 and a transparent conductive thin film 4 on the upper and lower sides of the conductive thin film. The substrate 11 is sandwiched between continuous electrodes in a square shape.
The switching circuit 7 fabricated above is one in which the MO8) transistor 5 and shift register 6 are integrated on a semiconductor substrate, and is mounted on the substrate 11 and connected to the photoelectric conversion element by a method such as wire bonding. be done.

Reading of a document image in such a document reading device is performed as follows.

Prior to entering the read cycle, the shift register 6 turns on the MOS transistors 5 in sequence, and the bias power supply 1 is turned on.
0, the light receiving element 1 is charged.

Next, when a reading cycle begins, the charge stored in the capacitor CD is discharged by the photodiode PD according to the amount of light incident on the light receiving element 1. Next, shift register 6
5MQS) The transistors 5 are sequentially turned on to recharge the capacitor CD, and the charging current at that time is transmitted to the signal line 8 and further amplified by the amplifier 12 to read optical information. That is, a current for recharging flows in the portions that are discharged due to exposure to light, and no charging current flows unless discharge occurs in the black portions.

In this manner, the original can be read using the light receiving element section.

By the way, in the conventional document reading device as described above, all the photoelectric conversion elements 1 in the document reading device are commonly connected to each signal line 8 via separate MOS transistors 5. Moreover, the capacitance of the signal line has become extremely large. Therefore, since the time constant of the continuous circuit formed by the signal line 8 and the amplifier 12 is large, it is difficult to read out the signal by short-time switching, which is a major obstacle to increasing the reading speed. was. −
This invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a document reading device that can read documents at high speed by reducing the capacity of a readout signal line.

That is, in this invention, a plurality of first switching elements such as transistors are provided in a one-to-one correspondence with each photoelectric conversion element so as to switch each photoelectric conversion output from the photoelectric conversion element; The output electrodes of the switching elements are commonly connected for each divided block, and the switching outputs of the plurality of photoelectric conversion outputs obtained through the common connection line are read out for each block. The device is provided with one second switch element, each output electrode of the second switch element is commonly connected, and each photoelectric conversion output is obtained via the commonly connected signal line. . Thereby, the number of switch elements directly connected to the final output signal line can be reduced, and the signal line capacitance can be reduced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A document reading device according to the present invention will be described in detail below with reference to embodiments shown in the accompanying drawings.

FIG. 2 shows an embodiment of the document reading device according to the present invention. In addition, in FIG. 2, elements or circuits that have the same functions as the elements or circuits shown in FIG. 1 are shown with the same or corresponding numbers and symbols, and duplicate explanations will be omitted. . Further, in this embodiment circuit, for convenience, a document reading device having nine photoelectric conversion elements is shown.

In FIG. 2, 1a to 11 are equivalent circuits of photoelectric conversion elements, and 5a to 5 are connected to these in one-to-one correspondence.
Reference numeral 1 denotes a switch element composed of, for example, a MOS transistor. These switch elements 53 to 51 share several adjacent output electrodes (in this example, three) to form one block, and each includes second switch elements 9A, 9B, each composed of, for example, a MOS transistor. Connected to the input electrode of 9C. In addition, the switch elements 53 to
Each gate electrode 51 is connected to each parallel output line of the shift register 6. Furthermore, second switch elements 9A to 9
Each gate electrode of C is connected to each output terminal of gates 20A to 20C, respectively.
On/off control of the switch elements 9A to 9C is performed based on each output signal.

That is, the gate 20A is configured such that a switching pulse for reading out the photoelectric conversion output of one of the photoelectric conversion elements 1a to 1c from the shift register 6 is applied to the first switch element 5.
a to 5c, the gate 20B operates to apply a switching pulse for turning on the second switching element 9A to the gate electrode of the switching element 9A, and the gate 20B receives photoelectric conversion from the shift register 6. The switching palace for reading out the photoelectric conversion output of any one of the elements 1a to 1c is the first switching element 5d to
5f, a switching pulse for turning on the second switching element 9B is applied to the switching element 9B.
It operates in such a way that it is added to the gate electrode of Goo)
Similarly, 20C corresponds to the switching element 7C for reading out the photoelectric conversion elements Ig, lh, and li. therefore,
In this embodiment circuit, when the signal output from the shift register 6 is at a low logic level, the first switch elements 58 to 5j and the second switch elements 9A to 9C are respectively turned on. Then, the second switch element 9
Each photoelectric conversion output read out by A to 9C is input to the amplifier 12 via the common connection line 8 of the switch elements 98 to 9C, and after being appropriately amplified, is outputted as a final read signal via the terminal 15. Ru.

With this configuration, the number of switch elements directly connected to the signal line 8 can be reduced, and the capacitance of the signal line 8 can be reduced.

For example, assume that a document reading device has 2048 photoelectric conversion elements.

In this case, assuming that the drain capacitance of the first switching element connected to each photoelectric conversion element is 1 picofarad (PF), the conventional In the circuit, the signal line capacity is 204
8 PF.

On the other hand, based on the present invention, the 2048 first switching elements are divided into 16 blocks each having 128 elements, each block is provided with a common second switching element, and the 16 second switching elements are divided into 16 blocks each having 128 elements. When the switching elements are commonly connected to obtain a signal output, the number of switching elements connected to the signal line 8 by one switching is 128 for the first switching element and 128 for the second switching element. The total number of switching elements including 16 is 144, and as a result, the capacitance of the signal line 8 is 144PF.Therefore, the time constant at the time of signal reading can also be made to have a rising time with equal constraints.

Note that in this embodiment circuit, a normal IC (MOS) transistor is used as a switch element, but a thin film transistor formed integrally with a photoelectric conversion element may also be used as the switch element.

As explained above, according to the document reading device according to the present invention, by reducing the capacity of the readout signal line,
High-speed document reading becomes possible.

[Brief explanation of the drawing]

Figure 1 (aJ is an equivalent circuit diagram of a conventional document reading device,
2 is a structural plan view of the document reading device shown in FIG. 1(a), FIG. 1(C) is a sectional view taken along line A-A' in FIG. FIG. 2 is an equivalent circuit diagram showing one embodiment of the present invention. j... Photoelectric conversion element, 2... Divided electrode, 3... Photoconductor, 4... Transparent conductive thin film, 5... MOS transistor which is the first switch element, 6... Shift register , 7... Switching circuit, 8... Signal line, 1o
...bias power supply, 11.substrate, 12.amplifier,
9A, 9B.

Claims (1)

[Claims] A plurality of lower layer electrodes are provided on a substrate, and a photoconductor and a transparent conductive upper layer electrode are provided thereon to form a plurality of photoelectric conversion elements, and each photoelectric conversion output from the photoelectric conversion elements is transferred to a first switch means. In a document reading device that performs pj switching and outputs to a signal line,
A second device that divides the signal line into a plurality of signal lines and outputs respective photoelectric conversion outputs corresponding to the plurality of divided signal lines.
What is claimed is: 1. A document reading device characterized in that a switch means is provided.