JPH05300308A - Image sensor - Google Patents

Abstract

PURPOSE:To make the read spied variable by easily changing an amplification factor of an amplifier circuit in the image sensor. CONSTITUTION:A signal from a picture element section comprising plural light receiving elements connected in parallel is sequentially switched at an analog switch section by a control signal from a shift register and the signal is outputted from a serial signal. Two resistors R2, R3 are connected to an output terminal of an operational amplifier 18a. The resistor R2 connects to ground and the resistor R3 is provided with a grounding use external terminal 20. The amplification factor is changed by using the grounding use external terminal 20 to connect the resistor R3 to ground so as to be in response to a change in a read speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor, and more particularly to an image sensor capable of changing a reading speed in two steps.

[0002]

2. Description of the Related Art Conventionally, an image sensor in which a plurality of light receiving elements such as phototransistors and photodiodes are arranged side by side has been used for FAX machines and the like. In such an image sensor, a pixel unit in which light receiving elements are normally arranged in parallel, an analog switch unit for sequentially switching and outputting signals from the pixel unit, and a control signal for controlling opening / closing of the analog switch. Is formed on one chip. Since the analog signal from the pixel portion is generally extremely small, an analog amplifier circuit for amplifying this analog signal is used.

FIG. 3 shows a circuit configuration of a conventional image sensor. A plurality of light receiving elements (photodiodes and phototransistors) are arranged in parallel in the pixel section 10, and a voltage Vdd is applied to these light receiving elements. When light corresponding to the light and shade of a document enters each light receiving element, each light receiving element outputs a voltage according to the amount of incident light. Then, the signal from the pixel unit 10 is input to the analog switch unit 12. The analog switch unit 12 is composed of a plurality of transistors connected to each light receiving element. By sequentially controlling ON / OFF of these transistors, the signal from each light receiving element is switched to be a serial output. ON / OFF control of the transistor is performed by the shift register 14. That is, the control signal S is sent to the shift register 14.
By inputting I and the clock CLK and supplying the control signal SI to the base of the transistor, each transistor is turned on / off in order. The analog output from the analog switch unit 12 is supplied to the external capacitor 16.

FIG. 4 shows a timing chart of the control signal SI, the clock CLK and the analog output AO. When the control signal SI is Hi, the analog switch is O
N, the output signal from the corresponding light receiving element is supplied to the external capacitor 16, and the charge is accumulated. And
The external capacitor 16 is discharged in synchronization with the clock CLK and output as an analog output AO.

The analog output AO from the external capacitor 16 is supplied to the analog amplifier circuit 18 including the OP amplifier 18a, amplified by the amplification factor determined by the resistors R1 and R2, and then output.

[0006]

When such an image sensor is used by being incorporated in, for example, a FAX or the like, it is necessary to prepare the reading speed in a plurality of stages (for example, 1 line 5 ms and 1 line 10 ms) according to the user's request. May occur. To change the reading speed,
It suffices to change the switching speed in the analog switch section. However, when the reading speed is 5 ms / L, the amount of electric charge accumulated in the external capacitor 16 is almost half that in the reading speed of 10 ms / L. However, when the amplification rate of the analog amplification circuit 18 is set for the reading speed of 10 ms / L, there is a problem that the amplification rate becomes insufficient and post-processing (A / D conversion, etc.) is hindered.

Therefore, the amplification factor of the analog amplifier circuit must be uniquely determined according to the reading speed, and the reading speed is appropriately changed on the user side (reading speed 5 ms / L to 10 ms / L, Or vice versa)
There was a problem I could not do.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide an image sensor capable of easily changing the reading speed.

[0009]

In order to achieve the above object, the present invention switches and outputs a signal from a pixel portion in which a plurality of light receiving elements are arranged in parallel, and outputs this output signal by an amplifier circuit. In an image sensor that amplifies and outputs as a pixel signal, two resistors having different resistance values are connected in parallel to each other to the amplifier circuit, one of the two resistors is grounded, and the other of the two resistors is grounded. It has an external terminal for use, and the amplification factor of the amplification circuit is changed by grounding the other of the two resistors.

[0010]

In the image sensor of the present invention, two resistors connected in parallel to each other are connected to the amplifier circuit, and the gain of the amplifier circuit is changed in two stages by the two resistors.

That is, the amplification factor obtained when either of the two resistors is grounded is made to correspond to one reading speed, and the two resistors are grounded together to obtain the combined resistance of the two resistors. If the amplification factor is associated with another reading speed, the reading speed can be freely changed depending on whether or not the two resistors are both grounded.

Here, one of the two resistors is grounded in advance. Since the external terminal for grounding is provided on the other side, it becomes possible for the user to easily ground both resistors together.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the image sensor according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit diagram of the image sensor in this embodiment. The sensor chip includes the pixel unit 10, the analog switch unit 12, and the shift register 14 shown in FIG. Although the external capacitor 16 is not shown in FIG. 1 for convenience, it is connected to the sensor chip as in FIG. Then, the analog output AO from this sensor chip (specifically, an external capacitor) becomes O.
It is input to the non-inverting input terminal of the P amplifier 18a, amplified, and then output.

Here, a characteristic of this embodiment is that two resistors R, which have different resistance values and are connected in parallel with each other, are provided in an amplifier circuit composed of an OP amplifier 18a and a resistor R.
2 and R3 are connected. Of the two resistors, the resistor R2 is grounded and the resistor R3 is provided with a grounding external terminal 20. The resistance R is shown in FIG.
2, the resistor R3 and the sensor case 22 are schematically shown, and the user can easily ground the resistor R3 by soldering the grounding external terminal 20 of the resistor R3.

As shown in FIGS. 1 and 2, when only the resistor R2 of the two resistors is grounded, the amplification factor α of the OP amplifier 18a is α = 1 + R1 / R2. The amplification factor is set to correspond to the reading speed of 10 ms / L, for example. When the reading speed is set to 5 ms / L, the amplification factor needs to be about double that of the case of 5 ms / L as described above. Therefore, the grounding external terminal 20 of the resistor R3 is also used to ground the resistor R3. Let The amplification factor β at this time is β = 1 + R1 / R4, where 1 / R4 = 1 / R2 +
Since it becomes 1 / R3, it is possible to easily change the reading speed from 10 ms / L to 5 ms / L by setting the value of R3 so that 2α = β.

In this embodiment, the reading speed is 10 ms.
Although a case where the reading speed is changed from / L to a reading speed of 5 ms / L is illustrated, it goes without saying that the same can be changed in the opposite case.

[0018]

As described above, according to the image sensor of the present invention, the reading speed can be easily changed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a resistance according to the embodiment.

FIG. 3 is a circuit diagram of a conventional image sensor.

FIG. 4 is a timing chart showing the operation of a conventional image sensor.

[Explanation of symbols]

 10 Pixel Unit 12 Analog Switch Unit 14 Shift Register 18 Amplifying Circuit 18a OP Amplifier 20 External Terminal for Grounding

Claims (1)

[Claims] 1. An image sensor in which a signal from a pixel portion formed by arranging a plurality of light receiving elements is switched and controlled and output, and the output signal is amplified by an amplifier circuit and output as a pixel signal. Two resistors are connected in parallel to each other to the amplifier circuit, one of the two resistors is grounded, the other of the two resistors has an external terminal for grounding, and the other of the two resistors is An image sensor, wherein the amplification factor of the amplifier circuit is changed by grounding.