JP2876553B2 - Photoelectric conversion device and image reading device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion device and an image reading device, and more particularly, to reading out a photoelectrically converted signal from a photoelectric conversion element via a buffer means, to a readout signal. The present invention relates to a photoelectric conversion device and an image reading device that remove contained noise.

[Prior Art] Conventionally, when a photoelectric conversion device reads out a signal that has been photoelectrically converted from a photoelectric conversion element, an unnecessary component such as a dark signal or drive noise from the photoelectric conversion element may be included in the readout signal and output. Many. Here, the dark signal is a dark current of the optical sensor, and the driving noise is noise generated when the optical sensor is driven to read out a signal.

In order to remove noise from these photoelectric conversion elements, the present applicant has already proposed a photoelectric conversion device having the following configuration in Japanese Patent Application No. 62-279390.

FIG. 4 is a partial circuit diagram showing a configuration of the photoelectric conversion device.

In the figure, the noise from the photoelectric conversion element is stored in the capacitance C ₁ via the MOS transistor Qh _1, the signal from the photoelectric conversion element is stored in the capacitor C ₂ through the MOS transistor Qh _2.

Accumulated noise signal, a pulse phi _A, phi by MOS transistors Qh _3, MOS transistors Qh ₄ controlled by _B, the buffer amplifier respectively Qh _5, MOS transistor Q
It is sequentially transferred to the output signal line AL through h _9, to remove noise from the subsequent signal. As described above, by removing the noise from the photoelectric conversion element by removing the noise from the signal by passing the signal and the noise through the same amplifier, it is also possible to remove the offset noise generated in the amplifier at the same time.

The applicant has already filed Japanese Patent Application No. 63-72112,
A photoelectric conversion device having the following configuration has been proposed.

FIG. 5 is a partial circuit diagram showing a configuration of the photoelectric conversion device.

First, as shown in FIG. 5, the MOS transistors Qh, Qhr
Is turned on, _one of the capacitors C ₁ is grounded,
The MOS transistor _QVC is turned off, and the emitter of the photoelectric conversion element S is set in a floating state. Thus, the noise from the photoelectric conversion element S is stored in the capacitor C ₁ and capacitor C _V. The potential at this time is defined as Vn. Next, a signal is accumulated in the base of the photoelectric conversion element S, and a pulse φ _VC is raised during the accumulation period to clear the capacitor C _V. At this time, the potential changes from Vn to GND. Transistors Qh and Qhr are OFF
If you leave the state, the output-side potential of the capacitor C ₁ -Vn
Becomes

Next, the signal from the photoelectric conversion element S is transferred and accumulated in the capacitor _CV . At this time, the potential rises from GND by Vs. While the output side potential of the capacitor C ₁ increases by Vs from -Vn.

Here, when the transistor Qh is turned on, a signal from which a noise component has been removed can be output.

[Problems to be Solved by the Invention] However, in the above-mentioned photoelectric conversion device, the former photoelectric conversion device requires a high-precision external circuit to remove noise from the photoelectric conversion element and offset noise from the dot-sequential signal. A high-speed clamp circuit and a sample hold circuit are required. Further, when such a circuit is incorporated in the same chip, there is a problem that positive and negative pulses are required for the clamp circuit or the sample and hold pulse.

Further, the latter photoelectric conversion device has a problem that when an output signal is passed through a buffer amplifier, offset noise generated by the amplifier is superimposed.

An object of the present invention is to provide a photoelectric conversion device and an image reading device capable of removing both noise from a photoelectric conversion element and offset noise from a buffer amplifier.

[Means for Solving the Problems] A photoelectric conversion device of the present invention is provided for accumulating a photoelectric conversion element, a photoelectric conversion signal including a noise component from the photoelectric conversion element, and a noise component as separate charge signals. First and second storage means, buffer means for buffering charge signals from the first and second storage means, capacitance means connected to the buffer means, and an input side of the capacitance means Connected first reset means, second reset means connected to the output side of the capacitance means, and the input side and output side of the capacitance means are reset by the first and second reset means. Thereafter, the charge signal accumulated in the second accumulation means is passed through the buffer means while the first reset means is turned off and the output side of the capacitance means is reset by the second reset means. Then, after transferring the signal to the input side of the capacitance means, and then turning off the second reset means to make the output side of the capacitance means in a floating state, the charge signal accumulated in the first accumulation means is By transferring to the input side of the capacitance means via the buffer means, the first and second signals are transferred to the capacitance means.
Control means for forming a difference between the charge signals from the accumulating means, and controlling to remove noise included in the photoelectric conversion signal;
It is characterized by having.

An image reading apparatus according to an aspect of the invention includes an optical system that forms an optical image, a photoelectric conversion element that photoelectrically converts an optical image formed by the optical system, and a photoelectric conversion signal that includes a noise component from the photoelectric conversion element. First and second storage means for storing noise components as separate charge signals, buffer means for buffering charge signals from the first and second storage means, and connection to the buffer means The first reset means connected to the input side of the capacity means, the second reset means connected to the output side of the capacity means, and the first and second reset means. After resetting the input and output sides of the capacitance means, the first reset means is turned off, and the second storage means is reset in a state where the output side of the capacitance means is reset by the second reset means. Transferring the charge signal accumulated in the stage to the input side of the capacitance means through the buffer means, and then turning off the second reset means to float the output side of the capacitance means, The charge signal stored in the first storage means is transferred to the input side of the capacitance means via the buffer means, so that the first and second charge signals are transferred in the capacitance means.
Control means for forming a difference between the charge signals from the accumulating means, and controlling to remove noise included in the photoelectric conversion signal; and performing predetermined signal processing on the photoelectric conversion signal from which the noise has been removed, and then performing external processing. Signal processing means for outputting to the device.

[Operation] In the present invention, first, the input side and the output side of the capacitance means are reset by reset means provided on the input side and the output side of the capacitance means to have a predetermined potential (here, described as GND). In a state where the reset means on the input side is turned off and the output side of the capacitance means is reset by the reset means provided on the output side of the capacitance means, noise from the photoelectric conversion element is transmitted from the second storage means via the buffer means. (The potential at this time is Vn). Then, after the output side of the capacitance means is brought into a floating state, the input side of the capacitance means is reset by the reset means provided on the input side of the capacitance means. Is reset to a predetermined potential (here, described as GND). At this time, the potential on the input side of the capacitance means is from Vn to GND, and the potential on the output side of the capacitance means is-
Turns into Vn.

Next, the signal from the photoelectric conversion element is transferred from the first storage unit to the capacitor unit via the buffer unit (the potential at this time is set to Vs). At this time, the potential on the input side of the capacitance means changes from GND to Vs, and the potential on the output side of the capacitance means changes from -Vn to Vs.
It rises by s and becomes Vs−Vn.

Thus, noise from the photoelectric conversion element can be removed. At the same time, noise from the buffer means can be removed because both the signal and the noise from the photoelectric conversion element are subjected to the subtraction processing after passing through the same buffer means.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic circuit diagram of the photoelectric conversion device of the present invention.

As shown in the drawing, the photoelectric conversion element S is connected to the capacitor C _N via the MOS transistor T _1, also MOS transistors T
It is connected to the capacitor C _S through _2. Capacitors C _N and C _S are MOS transistors T _H1 and MOS controlled by a shift register.
It is connected to the MOS transistor T _BC, which is controlled by the buffer amplifier T _r2 and pulse phi _BC via the transistor T _H2. The shift register is controlled by pulses φ _HS , φ _H1 and φ _H2 .

The output of the buffer amplifier Tr ₂ is transferred to the output signal line SL. The output signal line SL has a parasitic capacitance C _H. The reset of the portion A on the output signal line SL side is performed by the MOS transistor _THBC controlled by the pulse φ _BC .

The output signal line SL includes a MOS transistor T _SH controlled by a pulse φ _H2 via a coupling capacitor C _C , and a pulse φ _HC1
Connected to a MOS transistor _THC1 controlled by MOS transistor T _HC1 do reset the output side of the B portion of the coupling capacitor C _C. MOS transistor T _SH is further connected to the capacitor C _S and the MOS transistors T _HC2. MOS transistor T _HC2 performs resetting of the C portion of the output side of the MOS transistor T _SH.

The first and second storage means are capacitances C _S and C _N , the buffer means is a buffer amplifier Tr ₂ , the capacitance means is a coupling capacitance C _C ,
The reset means corresponds to the MOS transistor T _HBC , the second reset means corresponds to the MOS transistor T _HC1 , and the control means corresponds to the means for generating the pulse φ _BC and the pulse φ _HC1 and the shift register.

Next, the operation of the photoelectric conversion device will be described with reference to FIG.

FIG. 2 is a timing chart for explaining the operation of the photoelectric conversion device.

First, the control pulse phi _T1, noise from the photoelectric conversion element S is stored in the capacitor C _N via the MOS transistor T _1. Further, by control of the pulse phi _T2, the signal from the photoelectric conversion element S is stored in the capacitor C _S through the MOS transistor T _2.

When the pulse phi _H1 becomes high level state MOS transistor T _H1 is turned ON, the noise accumulated in the capacitor C _N via MOS transistor T _H1, the buffer amplifier Tr _2,
It is stored in the coupling capacitance C _C. On the output side of the coupling capacitance C _C , the potential of the portion B is set such that the pulse φ _HC1 is in a high level state and the MOS
Since the transistor _THC1 is in the ON state, it is kept at GND. Therefore, the potential v ₁ of the A portion of the output signal line SL with respect to GND potential v ₂ of Part B, the noise voltage + Vn ₁ is accumulated.

Next, the pulse φ _{HC1 is set} to a low level, the MOS transistor T _HC1 is turned off, and the portion B is set in a floating state. Further, the pulse φ _{BC is set} to the high level, the MOS transistor _THBC is turned on, and the potential of the portion A is lowered from the noise voltage of + Vn ₁ to GND. At this time, the potential v ₂ of the portion B is + V
A noise voltage of −Vn _{1 having} a polarity opposite to that of the noise voltage of n ₁ is generated.

Next, a pulse phi _BC to the low level, after a MOS transistor T _HBC and OFF state, when the pulse phi _H2 to the high-level state, MOS transistor T _H2 is turned ON, is stored in the capacitance C _S signal MOS transistor T _H2 was, via a buffer amplifier Tr _2, are transferred to the coupling capacitor C _C.

Potential of the case A portion rises to the signal voltage Vs ₁ from GND. The potential of the part B becomes −Vn _{1 with the} rise of the potential of the part A.
Up from the noise voltage by voltage Vs _1, the Vs ₁ -Vn _1. That is, the potential becomes only the signal component in which the noise voltage component is canceled. Here, the sensor noise and the noise of the buffer amplifier have been removed.

Since the voltage Vs ₁ −Vn ₁ is generated in the portion B and the sample-and-hold MOS transistor _TSH is driven to the ON state, the voltage v ₃ is generated in the portion C. By the sample and hold, a signal with a high duty ratio and noise removed can be obtained.

FIG. 3 is a partial circuit diagram of the photoelectric conversion device of the present invention including a circuit for removing a pulse leakage component.

When a MOS transistor or the like is driven by a pulse, a pulse leakage component is generated due to pulse capacity division by a gate capacity of the MOS transistor or an overlapping capacity of a source (drain) and a gate and a signal line capacity. In addition, a pulse leakage component is also generated by the parasitic capacitance between the pulse wiring and the signal line. The above-described pulse leakage component can be removed from such a leakage component by providing a circuit having the same configuration in parallel with the signal readout circuit and performing a difference process as shown in FIG.

 Next, an example of an image reading apparatus to which the present invention is applied will be described.

FIG. 6 is a schematic configuration diagram of an example of an image reading apparatus.

In the figure, a document 501 is mechanically moved in a direction indicated by an arrow Y relative to a reading unit 505. Further, reading of an image is performed by scanning in the direction of the arrow X by the image sensor 504 as the photoelectric conversion device of the present invention.

First, the light from the light source 502 is reflected by the original 501, and the reflected light forms an image on the image sensor 504 through the imaging optical system 503. As a result, carriers corresponding to the intensity of the incident light are accumulated in the image sensor 504, photoelectrically converted, and output as image signals.

This image signal is digitally converted by the AD converter 506, and is taken into a memory in the image processing unit 507 as image data. Then, processing such as shading correction and color correction is performed and transmitted to the personal computer 508, a printer, or the like. The signal processing means includes the AD converter 506 and the image processing unit 5.
07 is applicable.

When the image signal transfer for the scanning in the X direction is completed in this manner,
By moving the document 501 relatively in the Y direction and repeating the same operation as described above, the previous image of the document 501 can be converted into an electric signal and extracted as image information.

In the above embodiments, the image reading apparatus using the line sensor has been described. However, the present invention is not limited to the line sensor, and can be used for, for example, an area sensor.

[Effects of the Invention] As described above in detail, according to the present invention, noise included in a signal from a photoelectric conversion element and offset noise generated by a buffer amplifier in a readout system are removed in the same chip. Became possible.

Also, by removing noise of the coupling capacitance type provided on the output side of the buffer amplifier, a bipolar transistor portion is included from the photoelectric conversion element to the buffer amplifier, and even if a bias voltage is applied, the bias voltage is offset. Can be.

Furthermore, by incorporating a sample-and-hold circuit, it became possible to output only a sensor signal with a good SN ratio.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram of the photoelectric conversion device of the present invention. FIG. 2 is a timing chart for explaining the operation of the photoelectric conversion device. FIG. 3 is a partial circuit diagram of the photoelectric conversion device of the present invention including a circuit for removing a pulse leakage component. FIG. 4 is a partial circuit diagram showing the configuration of the photoelectric conversion device disclosed in Japanese Patent Application No. 62-279390. FIG. 5 is a partial circuit diagram showing a configuration of the photoelectric conversion device disclosed in Japanese Patent Application No. 63-72112. FIG. 6 is a schematic configuration diagram of an example of an image reading apparatus. S: photoelectric conversion element, T ₁ , T ₂ , T _H1 , T _H2 , T _BC , T _HBC , T _SH ,
T _HC1 , T _HC2 : MOS transistor, Tr ₂ : buffer amplifier, C
_N, C _{S: volume, φ BC, φ H1, φ} H2, φ HC1, φ T1, φ T2:
Pulse, SL: output signal line, C _H : parasitic capacitance, C _C : coupling capacitance.

Claims (2)

(57) [Claims] 1. A photoelectric conversion element, first and second storage means for storing a photoelectric conversion signal including a noise component from the photoelectric conversion element and a noise component as separate charge signals, Buffer means for buffering charge signals from the first and second storage means; capacitance means connected to the buffer means; first reset means connected to the input side of the capacitance means; Second reset means connected to the output side of the means, and after the input and output sides of the capacitance means are reset by the first and second reset means, the first reset means is turned off; The charge signal stored in the second storage means is transferred to the input side of the capacitance means via the buffer means in a state where the output side of the capacitance means is reset by the second reset means. After turning off the second reset means to make the output side of the capacitance means in a floating state, the charge signal accumulated in the first accumulation means is transferred to the input side of the capacitance means via the buffer means. Control means for forming a difference between the charge signals from the first and second storage means in the capacitor means, and controlling to remove noise included in the photoelectric conversion signal. 2. An optical system for forming an optical image, a photoelectric conversion element for photoelectrically converting an optical image formed by the optical system, a photoelectric conversion signal including a noise component from the photoelectric conversion element, and a noise component First and second accumulation means for accumulating the charge signals as separate charge signals, buffer means for buffering charge signals from the first and second accumulation means, and a capacitor connected to the buffer means Means, first reset means connected to the input side of the capacity means, second reset means connected to the output side of the capacity means, and the capacity means by the first and second reset means After the input side and the output side are reset, the first reset means is turned off, and the output of the capacitance means is reset by the second reset means and stored in the second storage means. Transferred to the input side of the capacitance means via the buffer means, and then the second reset means is turned off to float the output side of the capacitance means, and then the first accumulation is performed. The difference between the charge signals from the first and second storage means is formed in the capacitance means by transferring the charge signal stored in the means to the input side of the capacitance means via the buffer means, and the photoelectric conversion is performed. Control means for controlling so as to remove noise contained in the signal; and signal processing means for performing predetermined signal processing on the photoelectric conversion signal from which the noise has been removed and outputting the signal to an external device. Image reading device.