JPH0413360A - Image sensor - Google Patents

Abstract

PURPOSE:The reduce after-image sufficiently and to attain reading with high quality by providing two photo transistor arrays being light receiving sections and providing a means delivering a base level of the 1st phototransistor(TR) array to a base of the 2nd photoTR array. CONSTITUTION:When an incident light strikes photoTRs 1, 2, during the integration period, a charge in a base-collector reverse junction is discharged, a base level is increased, and when no incident light comes, the base level is maintained. The base level is decreased in the charge state. When a white level original is read as a preliminary read line, the base level of the photoTR 1 rises, and when a switch 3 is turned on, the base level of the photoTR 2 rises. The photoTR 1 of the main read line increases the base level by reading a succeeding white original as the standby state and much output signal is obtained from the white level original. When the original is a black level original conversely, the base level of the photoTR 1 is decreased and when the switch 3 is closed, the base level of the photoTR 2 is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an image sensor for optically reading document information.

2. Description of the Related Art In recent years, image sensors have been developed for use in image input for office equipment, facsimile machines, digital copying machines, etc., and high-speed, high-precision reading is particularly required. An example of a conventional image sensor will be described below with reference to the drawings. FIG. 6 shows the basic circuit of a conventional image sensor.

In the figure, 101 is a phototransistor which is a light receiving element, and its base 109 is in a floating state. 1
02 is a charging PNP) transistor, 103 is a resistor, 1
04 is a power supply line, and 105 is an input terminal that receives a shift signal from the scanning circuit.

106 is a load resistance, 107 is an operational amplifier (hereinafter abbreviated as OP amplifier), 108 is an output terminal, and 1o6, 1
07 and 108 constitute an output circuit that converts the signal current from the phototransistor into a voltage. The operation of the image sensor made up of the above-mentioned components will be described below.

First, when a shift signal from the scanning circuit is applied to the input terminal 1o6, the base potential of the PNP transistor 101 decreases, and the PNP transistor 102 turns on.
A charging current flows into the phototransistor 101, and charges are accumulated in the base-collector reverse junction capacitance of the phototransistor 101. Next, when the shift signal from the scanning circuit disappears, the PIP l-transistor 102 is turned off, and charging of the phototransistor IQ1 is completed. After that, light corresponding to the density of the original is incident on the base-collector reverse junction of the phototransistor 101.
Discharges the charge accumulated in the base-collector reverse junction capacitance. After a certain integration time, when the shift signal from the scanning circuit is applied to the input terminal 106 again, the phototransistor 1o1 is charged by the operation described above. This charging current is output to the emitter of the phototransistor 1o1, is converted to rv in the output circuit, and an output corresponding to the density of the original appears at the output terminal 108 (for example, TV, 7th grade technical report Vol. 1.8 g2e B D 8129).

Problems to be Solved by the Invention However, in the above configuration, since the base of the phototransistor 101 is in a floating state, the base potential is not fixed and an afterimage occurs. In particular, when reading white after a long period of black without incident light, there is a problem in that it is difficult to generate an output signal. This will be explained below using FIG. 7. 7th
110 in Figure (a) indicates the state of light incident on the photo transistor IQ1; when it is white, light is incident, and when it is black, no light is incident, and each is repeated three times. shall be. 111 in FIG. 7 (bl) indicates a shift signal from the scanning 1 circuit. 112 in FIG. 7 (C) indicates the base potential of the phototransistor 101, which increases while light is incident; It remains constant while no light is incident, and decreases while a shift signal is applied and charging is performed. A charging current flows in accordance with this falling potential difference 113, and an output signal is obtained. The output signal is shown in FIG. 7(d) 7) 114. An ideal output signal with no afterimage is shown at 116 in FIG. 7 (θ). Ideal output (M number TH white signal 115a, 11
6b, 115C show the same value, black signal 11sd
, 11ese, and 11sf are not output, whereas the white signals 114a, 114b, 114C and the black signals 114d, 114e in FIG. 7(d).

A noticeable afterimage phenomenon appears in the white signal 114a after continuous black as in 114f and the black signal 114e after continuous white 114
The trajectory will be like g. For this reason, there was a problem in that the reading quality deteriorated.

The present invention has been made in order to improve the above-mentioned problems, and it is an object of the present invention to provide an image sensor with good reading quality by significantly reducing the afterimage phenomenon.

Means for Solving the Problems In order to achieve the above objects, the image sensor of the present invention has the following features:
Two rows of phototransistor arrays operating in charge accumulation mode are provided, the first row is used for preliminary reading, and the second row is used for main reading, and the document is assumed to move relatively from the first row to the second row. , the structure includes means for transmitting the base potential of each phototransistor in the first column to the base potential of each phototransistor in the second column.

According to the above-described structure, the present invention transmits the base potential of each phototransistor in the first column to the base potential of each phototransistor in the second column, thereby setting the phototransistor in advance before reading a white original. ) By raising the base potential of the transistor and lowering the base potential of the phototransistor before reading a black original, it is possible to obtain a video signal with minimal afterimages.

Embodiment Hereinafter, an image sensor according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the basic circuit of an image sensor in a first implementation series of the invention. In FIG. 1, 51 is a phototransistor, which is one in the second column phototransistor array. A phototransistor 2 is one in the first column phototransistor array, and the bases of the phototransistors 1 and 2 are connected to a switch 3. Although the switch 3 is represented by a contact symbol, an electronic switch is actually used. 4
・ is a PNP transistor for charging, and 6 is a resistor.

6 is a power supply terminal, 7 is a scanning: input terminal that receives a shift signal from the circuit, s d OP amplifier, 9 is a load resistor, 1o
is an output terminal, and 8, 9, and 10 constitute an output circuit that converts a signal current from the phototransistor 1 into a voltage.

Regarding the image sensor made up of the above-mentioned components, the relationship and operation of each component will be explained below with reference to FIGS. 1 and 2.

Reference numeral 11 shown in FIG. 2 flL) indicates light incident on the phototransistor, where white indicates light is incident and black indicates no light is incident. Shift signal from the 12'i scan circuit in Figure 2(b), 13'i phototransistor 2 in Figure 2(C)
It shows the base potential of 14 in Figure 1. When the base potential drops due to charging, a charging current flows in accordance with this drop value 14, and an output signal is obtained. 15 in Figure 2(d) is for l-)
1 in FIG. 2 (IL) shows the light incident on transistor 2.
It is delayed by 1 time T. This time T is the time during which the original to be scanned moves relatively between the first and second rows of phototransistors. 16 in Figure 2 (θ)
/:l: Indicates the base potential of the phototransistor 1. When the switch 3 is operated (HIGH-ON, LOW-OFF) at the timing shown in FIG. 2(f), the base potential of the phototransistor 1 is broken. become that way. The timing of turning on switch 3 is shown in Figure 2 (
K is performed after the pulse of the shift signal 12 in b) has completely risen. 19 in Figure 2(g) represents the signal output when the phototransistor 10 base is as shown in Figure (θ)■16.
FIG. 2 (20 in hl shows the signal output in the case of 17 in the base diagram (6) 7) of the phototransistor 1.

If there is incident light during the agitation period of phototransistors 1 and 2r'i, the charges in the base-collector reverse junction are discharged and the base potential rises; if there is no incident light, the base potential is maintained. In the charging state, the base potential .decreases. Also, the emitters dGND of phototransistors 1 and 2
Since it is a level, the higher the base potential, the more output signals are given. Preliminary continuation]! When the 12th line is a white original, the base potential of the transistor 1 rises, and when the switch 3 is turned on, the base of the phototransistor 20 rises.
Fru. The phototransistor 1 in the main reading line raises its base potential and enters a standby state when the next white document is read, so that more output signals can be obtained for the white document. Conversely, in the case of a black original, the base potential of the phototransistor 1 drops, and when the switch 3 is turned on, the base of the phototransistor 2 drops. The phototransistor 1 of the main reading line is in a standby state with its base potential lowered when the next black original is read, and no false output signal is generated for the black original. In other words, Figure 2 (phantom 19a (
White after continuous points) and 19d (black after continuous white) are improved as shown in FIG.

Hereinafter, one implementation of the second invention will be described with reference to the drawings. FIG. 3 is a basic circuit diagram of an image sensor showing a second embodiment. In the figure, there are PNP transistors 4 and 7 in the charging system of phototransistors 1 and 2, respectively.
a, 4b, resistor 5a.

6b, input terminals 7a and 7b are provided, and the configuration is such that charging can be performed at different timings, and the phototransistors 1,
The bases of 2 are connected by a resistor 21.

In FIG. 4, diodes 22 and 23 are connected between the bases of the phototransistor 1.2 so as to have opposite polarities, and this structure is the same as that in FIG. 3. The diode was used because the resistor 21 in Figure 3 requires a high resistance.
Since it is difficult to create on an integrated circuit, the high resistance near the rising point of the diode is used. Figure 6 ia),
(b) shows a shift signal applied to terminals 7b, 7& in FIG. After applying the shift signal (a) to the input terminal 7b,
The base potential of the phototransistor 2 for pre-reading which rose or fell: d is read via a resistor or diode, ! 7, a shift signal (bl) is applied to the input terminal 7a.

As mentioned above, the preliminary reading transistor 2,
The same effect as in the first embodiment can be obtained by connecting the bases of the main reading phototransistor 10 with a resistor or diode and applying the shift signal with a shifted phase.

Note that in each of the above columns, the elasticity of transistors (1)) may be reversed from those shown in the example, and in that case, the power supply polarity and the shift signal polarity may be changed accordingly.

Effects of the Invention As is clear from the above description of the embodiments, the present invention is an image sensor comprising a phototransistor array for reading an original that operates in a charge accumulation mode and a scanning circuit that scans each phototransistor. By providing two rows of the phototransistor array and providing means for transmitting the base potential of the phototransistors in the first row to the bases of the phototransistors in the second row, the afterimage phenomenon can be significantly reduced and high quality This provides an image sensor that can read υ.

[Brief explanation of the drawing]

FIG. 1 is a basic circuit diagram of an image sensor according to an embodiment of the first invention, FIG. 2 is a diagram showing input signals, potentials of various parts, etc. in the circuit of FIG. 1, and FIG. A basic circuit diagram of an image sensor according to an embodiment of the second invention, FIG. 4 is a circuit diagram showing an example in which the bases of the phototransistors shown in FIG. 3 are connected by a diode, and FIG. A shift signal diagram in one embodiment, FIG. 6 is a basic circuit diagram of a conventional image sensor, and FIG. 7 is a diagram showing input/output signals of the image sensor, potentials of various parts, etc. 1...Phototransistor for book reading, 2...
...Phototransistor for preliminary reading, 3...
・Base-to-base switch, 4, 41L, 4b...
Transistor, 6, 61L, 5b---Resistor, 7.71L, 7kl---Input terminal, 16.17
...Base potential, 21...Base-to-base resistance,
22.23...Base-to-base diode. Name of agent: Patent attorney Shigetaka Awano and one other person Susenin addition i word number 1? / fig fig fig (ilm) (shi)

Claims (5)

[Claims] (1) An image sensor consisting of a phototransistor array for reading an original that operates in a charge accumulation mode and a scanning circuit that scans each phototransistor, in which two rows of the phototransistor arrays serving as light receiving sections are provided, and a first
An image sensor having means for transmitting a base potential of a phototransistor in a column to a base of a phototransistor in a second column. (2) A switch is used as the means for transmitting the base potential, and after reading out the phototransistors in the second column, the switch is made conductive to transmit the base potential of the phototransistors in the first column to the base potential of the phototransistors in the second column. Item 1
The image sensor described. (3) A charging system for the first row of phototransistors and a charging system for the second row of phototransistors are provided, and by charging the first row of phototransistors and then charging the second row of phototransistors, the first row of phototransistors can be charged. 2. The image sensor according to claim 1, wherein the base potential of the phototransistor in the second column is transmitted to the base of the phototransistor in the second column. (4) Claim 3 in which the bases of the phototransistors in the first row and the bases of the phototransistors in the second row are connected by a resistor.
The image sensor described. (5) The image sensor according to claim 3, wherein the bases of the phototransistors in the first row and the bases of the phototransistors in the second row are connected by a diode.