JPH0247979A - Picture reader - Google Patents

Abstract

PURPOSE:To attain proper adjustment of an amplification factor of an amplifier in response to the kind of a photoelectric conversion element by switching a resistor deciding the amplification factor of the amplifier with a switch element turned on/off with an external signal. CONSTITUTION:A resistor 13a at an amplification section A is connected to the circuit when switch elements 15, 16 at both ends of the resistor 13a are turned on. Similarly, a resistor 13b is connected to the circuit when switch elements 17, 18 are turned on and a resistor 13c is connected to the circuit when switch elements 19, 20 are turned on respectively. The on/off of the switches are implemented by signals from resistor selection signal input terminals 14a-14c. Thus, the resistors 13a-13c are switched properly in response to the kind of an operational amplifier 10.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an image reading device used in facsimiles, scanners, and the like.

[Conventional technology]

As a large-area image reading device, there is a contact image sensor that projects and reads a document in its original size (1:1). FIG. 4 shows a conventional image reading device. In FIG. 4, l is a photoelectric conversion element (photodiode), 2 is the equivalent capacitance of the photoelectric conversion element 1, 3 is a reset switch, 4 is a buffer amplifier, 5 is a read signal changeover switch, 6 is a negative power supply,
7 is a reset line, 8 is a common output line, 9 is a scanning circuit, 10
is an operational amplifier, 11 is an output terminal, 12.13 is a resistor, A
is the amplification section. The photoelectric conversion element 1 is used with a reverse bias applied thereto. Electricity purchase [6] is for this purpose. The equivalent capacitance 2 is a capacitance that isometrically represents the total of the capacitance between the bridges of the photoelectric conversion element 1, the stray capacitance generated along with the wiring of the photoelectric conversion element 1, and the like. Reset switch 3 is equivalent! The buffer amplifier 4 is used for impedance conversion. The read signal switching switch 5 is a switch for reading out the detected value, that is, the potential of the equivalent capacitance 2. The potential of the equivalent capacitance 2 changes depending on the light incident on the charging conversion element 1, as described below. Next, the operation will be explained. When the reset switch 3 is turned on, a current flows through the path of earth-reset switch 3 -> equivalent capacitance 2 -> negative power supply 6 (-V), and the equivalent capacitance 2 is charged to the polarity shown. When light is incident on the photoelectric conversion element 1, a photocurrent with an intensity corresponding to the incident light flows in the opposite direction of the photoelectric conversion element I, and the equivalent capacitance 2 is discharged. When the read signal changeover switch 5 is turned on at a predetermined time, the potential of the equivalent capacitance 2 at that time is read out via the buffer amplifier 4 (the amount of charge in the equivalent capacitance 2 is small, so it is not suitable for reading out with a current. , read out as a voltage using a buffer amplifier with high input impedance). Since the value as read is small, it is amplified by the amplifying section A. The intensity of the incident light can be determined from the output obtained at the output terminal 11 in this manner. The reset switch 3 and each read signal changeover switch 5 in FIG. 4 are not turned on and off all at once, but the scanning circuit 9
The signals are sequentially switched by a signal S that controls the reset switch 3 from the signal S and a signal S that controls the read signal changeover switch 5 . The scanning circuit 9 is composed of, for example, a shift register.

[Problem to be solved by the invention]

(Problem) In the conventional image reading device described above, the amplification degree (gain) of the amplifying section A is a fixed value. There was a problem in that there were cases where it was not possible to amplify the signal. (Description of the Problem) As is well known, the amplification degree of the amplifying section A in FIG. 4 is determined by the ratio of the resistor 13 to the resistor 12 (this is related to the amount of feedback). For example, if the ratio is 1,
The amplification degree is 2. However, the resistors 12 and 13 are built into the IC chip, and their values are fixed values. Therefore, the amplification degree of the amplifying section A is one specific value. However, depending on the type of photoelectric conversion element 1 connected thereto, the readout output may be small and cannot be amplified to an appropriate level with the above amplification degree. An object of the present invention is to solve the above-mentioned problems.

[Means to solve the problem]

In order to solve the above problems, the present invention includes a charging conversion element, a reset switch that discharges the charge of the equivalent capacitance of the photoelectric conversion element, and amplifying the potential of the equivalent capacitance read out through a read signal changeover switch. In an image reading apparatus equipped with an amplifying section, the resistor that determines the degree of amplification of the amplifying section is selectively switched by a switch element that is turned on and off by an external signal.

[For production]

Generally, the amplification degree of the amplification section is determined according to the amount of feedback. The amount of feedback is usually controlled by a resistance. Several resistors that can be selectively switched are provided in the amplification section of the image reading device, and these are selected by a switch element that is turned on and off by an external signal. Then, the degree of amplification of the amplification section will depend on the selected resistance. In other words, the amplification degree of the amplification section of the image reading device is
It can be adjusted to a desired value from the outside.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an image reading apparatus according to an embodiment of the present invention. Reference numerals in FIG. 1 correspond to those in FIG. 4. And 13a to 13c are resistors, 14a to 14c
1 is a resistance selection signal input terminal, and 15 to 20 are switch elements. The difference in configuration from the conventional one (Fig. 4) is that the amplifying section A
The composition is as follows. That is, the part corresponding to the conventional resistor 13 is replaced with a configuration in which three series circuits of a switch element and a resistor are connected in parallel. The resistor 13a is connected to the circuit when the switch elements 15, 16 at both ends are turned on. Similarly, resistor 13b is connected to the circuit when switch element 17.18 is turned on, and resistor 13c is connected to the circuit when switch 19.20 is turned on. The switching elements 15 and 16 are turned on and off by the resistance selection signal input terminal 14a. Similarly, the switching elements 17.18 are activated by the resistance selection signal input terminal 14b, and the switching elements 19.20 are activated by the resistance selection signal input terminal 1.
4c. There are the following seven types of connection methods for connecting which of the resistors 13a to 13c to the circuit. (a) When connecting each resistor individually...3 types (b)
When connecting two resistors in combination...Three types (c) When connecting all three...IfI type, that is, the amplification degree can be switched to seven types. Therefore, an appropriate degree of amplification can be achieved by applying a signal from the outside to the resistance selection signal input terminals 14a to 14c depending on the type of the connected photoelectric conversion element 1. In the example shown in Figure 1, the number of resistors to be switched is three, but this number is not limited to three; it can be increased or decreased as needed. good. Furthermore, the configuration of the amplifier section A is not limited to the type in which feedback is provided to the inverting terminal of the operational amplifier 10, but may be in other types. FIGS. 2 and 3 show other examples of the amplifying section. FIG. 2 shows a type of feedback to the non-inverting terminal of the operational amplifier IO. The resistors 13d to 13f are switched and connected by switch elements 21 to 26 to change the resistance ratio with respect to the resistor 12-1 connected to the read signal input terminal 33. Note that 14d to 14f are resistance selection signal input terminals. FIG. 3 shows a type of differential amplifier. The same reference numerals as in FIG. 2 correspond to those in FIG. 1
2-2 is a resistor, 13g to 13i are resistors, 27 to 32 are switch elements, and 34 is a reference potential input terminal. A reference potential is input to the inverting terminal side of the operational amplifier 10, and a read signal is input to the non-inverting terminal side. By appropriately switching and connecting the resistors 134 to 13i, differential amplification can be performed with an appropriate amplification degree. Note that the resistors 13d and 13g share the resistor selection signal input to the resistor selection signal input terminal 14d and are turned on and off at the same time, but they may not be used in common, and they may not necessarily be switched on or off at the same time. It is not necessary to combine the resistors and turn them on at the same time; in short, it is only necessary to appropriately combine the resistors using an external resistor selection signal to obtain an appropriate amplification degree as a result.

【Effect of the invention】

As described above, according to the present invention, in the image reading device, the resistance that determines the amplification degree of the amplification section is selectively switched by a switch element that is turned on and off by an external signal. It is now possible to adjust the power from the outside so that it is appropriate for the type of photoelectric conversion element connected.

[Brief explanation of the drawing]

Fig. 1... Image reading device according to an embodiment of the present invention Fig. 2, Fig. 3... Other examples of amplifier sections Fig. 4... In the diagram of a conventional image reading device, 1 is a charging conversion element, 2 is an equivalent capacitance, 3 is a reset switch, 4 is a buffer amplifier, 5 is a read signal changeover switch, 6 is a negative power supply, 7 is a reset line, 8 is a common output line, 9 is a scanning circuit, 10 is an operational amplifier, 11 is an output terminal, 12.13 and l3a to 131 are resistors, 14
a to 14f are resistance selection signal input terminals, 15 to 3
2 is a switch element, 33 is a read signal input terminal, and 34 is a reference potential input terminal.

Claims (1)

[Claims] An image reading device comprising a photoelectric conversion element, a reset switch that discharges the charge of the equivalent capacitance of the photoelectric conversion element, and an amplification section that amplifies the potential of the equivalent capacitance read out via the read signal changeover switch, An image reading device characterized in that a resistor that determines the degree of amplification of the amplification section is selectively switched by a switch element that is turned on and off by an external signal.