JP3332026B2 - Photoelectric conversion device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a photoelectric conversion device, and more particularly, to an improvement in a photoelectric conversion device used for an image reading device or the like, which corrects a dark current characteristic of a photoelectric conversion element. .

[0002]

2. Description of the Related Art FIG. 15 is a diagram showing a configuration of a conventional photoelectric conversion device. This photoelectric conversion device is used, for example, in an image reading device that reads a document image based on reflected light of an LED reflected on a paper document. This photoelectric conversion device,
Many photoelectric conversion circuits 11, 12, 13,... Surrounded by broken lines.
An output transistor Vot, an A / D conversion circuit 4,
It is composed of a digital processing circuit 5 such as a CPU. The detection signal of each photoelectric conversion circuit is amplified by the output transistor Vot, converted into digital data by the A / D conversion circuit 2, and then input to the digital processing circuit 3.

The photoelectric conversion circuit 11 includes a photodiode sensor S1, an initialization switch ASW1, and an output switch S
W1, transistor TR1, and constant current source I1. The sensor S1 has an anode terminal grounded, a cathode terminal connected to the gate terminal of the transistor TR1, and is connected to the power supply PS via the switch ASW1. The transistor TR1 has a drain terminal connected to the power supply P.
S, the source terminal is connected to the gate of the output transistor Vot via SW1, and to the grounded current source I1. The photoelectric conversion circuits 12, 13,... Are also configured as the same circuit as the photoelectric conversion circuit 11.

[0004] The operation of this photoelectric conversion device will be described. First, before irradiating light to the photodiode sensor S1, the initialization switch ASW1 is turned on to apply a reset voltage to the sensor S1. After that, the initialization switch AS
When light is applied to the sensor S1 after W1 is turned off, charges corresponding to the light intensity are accumulated by the photoelectric effect. The accumulation of the charge changes the gate voltage of the transistor TR1 and applies a voltage to the source terminal of the transistor TR1. At this time, the level shift voltage from the gate terminal to the source terminal is determined by the current source I1.

When the output switch SW1 is turned on, the detection signal of the photoelectric conversion circuit 11 is output to the output transistor V
ot can be given as a gate voltage. As a result, the voltage after photoelectric conversion reflecting the optical information can be output to the digital processing circuit 5 via the A / D conversion circuit 4. In this photoelectric conversion device, each photoelectric conversion circuit 11, 1
2, 13, ... share the output transistor Vot,
Output switches SW1, SW2, SW3 of each photoelectric conversion circuit
.. Are sequentially turned on so that each photoelectric conversion circuit (each bit)
Can be sequentially read out.

Next, shading correction performed by the digital processing circuit 5 on the detection signal after A / D conversion will be described. First, A / D conversion is performed for each photoelectric conversion circuit (each pixel).
The converted dark output level Vd (n) and light output level V
p (n) is measured in advance, and a correction coefficient K (n) for each pixel is obtained in advance by the following equation. K (n) = 2 ^m / {Vp (n) −Vd (n)} × 2 ^(m−1)

Here, Vd (n) in the figure is L for light irradiation.
Vp (n) is a detection signal when the LED for light irradiation is turned on and a white reference original is read when ED (not shown) is turned off. Also, m is A
/ D conversion circuit 4 is the number of effective output bits, 2 ^(m-1) ≤
K (n) ≦ 2 ^m holds. The dark output level Vd (n) and the correction coefficient K (n) thus obtained are stored in a memory (not shown) in advance.

When an original is read by turning on a light irradiation LED (not shown), a detection signal for each pixel is set to Vg (n).
Then, the digital processing circuit 5 performs an operation on the basis of the following equation to obtain the corrected image data Dg for each pixel.
Find (n). Dg (n) = {Vg (n) −Vd (n)} × K (n) / 2 ^(m−1) That is, based on the detection signal Vg (n) after the A / D conversion,
Using the dark output Vd (n) and the correction coefficient K (n) on the memory, m-bit-accurate image data Dg (n) is obtained.

[0009] An example of a conventional photoelectric conversion device is also disclosed in Japanese Patent Application Laid-Open No. 3-58229.

[0010]

The conventional photoelectric conversion device is configured as described above, and has a manufacturing variation because the photoelectric conversion element is made of a semiconductor. That is, there is a problem that the characteristics of the photoelectric conversion element, for example, the characteristics of the photodiode sensor S1 vary.

When a photodiode is used as the photoelectric conversion element, the detection signal may be out of the correctable range of the digital processing circuit 5 due to the variation of the dark output itself or the temperature change of the dark output. In such a case, there is also a problem that the image quality is deteriorated due to insufficient correction.

FIG. 16 is a diagram showing an example of the temperature-dark output characteristic of the photodiode sensor. It can be seen that the dark output increases as the temperature rises. FIG. 17 is a diagram illustrating an example of the detection signals at different temperatures T0 and T1. At the temperature T0, the detection signal is within the correction range, but at the higher temperature T1, the detection signal is out of the correction range, so that the detection signal exceeds the operation range of the digital processing circuit 3 and the digitization of the digital signal occurs. I do. As described above, the image quality is deteriorated due to the temperature change.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an apparatus capable of improving the image quality of an image reading apparatus and maintaining the image quality even with a change in temperature. The purpose is to get.

[0014]

A photoelectric conversion device according to the present invention comprises a first photodiode for photoelectrically converting irradiation light to generate a detection signal, and the first photodiode is initialized.
A photoelectric conversion circuit comprising first switch means for performing
A second photodiode having substantially the same characteristics as the first photodiode.
Photodiode, initializes this second photodiode
And second switch means for switching the first and second switches.
The operation timing of the switching means, and
The photoelectric conversion period of the photodiode is changed to the photoelectric conversion period of the first photodiode.
A reference circuit that generates a detection signal of the photoelectric conversion circuit when the irradiation is not performed by equalization by making the conversion period shorter, and a correction circuit that performs dark correction of the detection signal of the photoelectric conversion circuit based on the detection signal of the reference circuit. It is provided with.

In the photoelectric conversion device according to the present invention, the correction circuit includes a differential circuit to which a detection signal of the photoelectric conversion circuit and a detection signal of the reference circuit are input, and the photoelectric conversion circuit and the reference circuit synchronize the detection signal. And output it.

Further, the photoelectric conversion device according to the present invention includes two or more photoelectric conversion circuits having different output timings of the detection signals, and the correction circuit detects the darkness of the detection signals of these photoelectric conversion circuits based on the detection signals of the reference circuit. The correction is performed sequentially.

The photoelectric conversion device according to the present invention comprises a plurality of photoelectric conversion circuits, the first photodiodes are arranged in a substantially straight line, and a reference circuit is arranged for every 10 to 50 photoelectric conversion circuits. Is done.

In the photoelectric conversion device according to the present invention, the photoelectric conversion circuit and the reference circuit generate a detection signal as a current signal, and the correction circuit outputs a current value equal to the current signal of the reference circuit via the current mirror circuit. It is configured to subtract from the current signal of the conversion circuit.

Further, the photoelectric conversion device according to the present invention includes two or more photoelectric conversion circuits having different output timings of the detection signal, and the correction circuit amplifies the current signal from one reference circuit, and outputs two or more photoelectric conversion circuits. Is configured to be subtracted from the current signal.

Further, the photoelectric conversion device according to the present invention includes a plurality of photoelectric conversion circuits, the first photodiodes are arranged substantially linearly, and the reference circuit is arranged for every 4 to 16 photoelectric conversion circuits. Be composed.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a diagram showing a configuration example of a photoelectric conversion device according to the present invention. This photoelectric conversion device includes a photoelectric conversion circuit 1, an output transistor Vot1, a reference circuit 2, an output transistor Vot2, a differential circuit 3, an A / D conversion circuit 4, and a digital processing circuit 5. You. In the differential circuit 3 as a correction circuit, a difference between the detection signal of the photoelectric conversion circuit 1 and the output signal of the reference circuit 2 is obtained, and after the difference signal is converted into digital data by the A / D conversion circuit 4, , Are input to the digital processing circuit 5.

The configuration of the photoelectric conversion circuit 1 is the same as that of the photoelectric conversion circuit 11 shown in FIG. The configuration of the reference circuit 2 is the same, but differs from the reading sensor S of the photoelectric conversion circuit 1 in that the light receiving surface of the reference sensor SR is shielded from light.
The differential circuit 3 is a general differential amplifier composed of resistors R1 to R4 and an OP amplifier A1.

The operation of the photoelectric conversion device will be described. First, the initialization switches ASW and ASWR are both set to O.
N, and after applying the same initialization voltage to the reading sensor S and the reference sensor SR, the initialization switch is turned ON at the same timing.
F.

When light is applied to the reading sensor S after the initialization switch ASW is turned off, charges corresponding to the light intensity are accumulated, the gate voltage of the transistor TR1 changes, and a voltage is applied to the source terminal of the transistor TR. That is, the transistor TR as the voltage-current conversion means converts the gate voltage into a current, and this converted current is used as the current source I
Flow into The level shift voltage from the gate terminal to the source terminal of the transistor TR is defined by the current source I, and a voltage is applied to the source terminal of the transistor TR.

On the other hand, the reference sensor SR always leaks a small current even in a state where no light is applied. Therefore, after the initialization switch ASWR is turned off, the reference sensor S
Although no light strikes R, the gate voltage of the transistor TRR fluctuates. Then, as in the case of the photoelectric conversion circuit 1,
A voltage is applied to the source terminal of the transistor TRR by a level shift voltage from the gate terminal to the source terminal determined by the current source IR.

Next, the output switches SW and SWR are turned on at the same timing. At this time, the output signal of the photoelectric conversion circuit 1 is given as the gate voltage of the output transistor Vot1, and the amplified signal is input to one input terminal of the differential circuit 3. Further, the output signal of the reference circuit 2 is given as the gate voltage of the output transistor Vot2, and the amplified signal is input to the other input terminal of the differential circuit 3. Then, the differential circuit 3 calculates the voltage difference between these amplified signals.

According to the present embodiment, since the reference circuit 2 generates a detection signal (ie, dark output) when the photoelectric conversion circuit 1 is not irradiated, the dark output characteristics can be corrected in a real time. . Further, since the dark output correction is performed in the state of the analog signal before the A / D conversion of the detection signal, the detection signal deviates from a predetermined correction range, and the influence of the digit cancellation in the digital processing circuit is reduced. I will not receive it. Further, the photoelectric conversion circuit 1 and the reference circuit 2
The temperature characteristics of the photoelectric conversion elements can be offset by calculating the difference between the output signals of the two sensors using photoelectric conversion elements having the same or substantially the same characteristics.

Embodiment 2 In this embodiment, a photoelectric conversion device including a plurality of photoelectric conversion circuits and a plurality of reference circuits will be described. 2 and 3 are views showing one configuration example of the photoelectric conversion device according to the present invention. FIG. 2 shows n (n is 2 or more) reading sensors S
1 to Sn are linearly arranged, and 1
FIG. 3 is a diagram illustrating a state in which a plurality of reference sensors SR1 to SRn corresponding to the pair 1 are linearly arranged in the vicinity of each reading sensor, and FIG. 3 is a diagram illustrating a circuit configuration thereof.

The photoelectric conversion circuit 11 surrounded by a broken line is shown in FIG.
, And such a photoelectric conversion circuit is provided for each of the reading sensors S1 to Sn. The detection signals output from the photoelectric conversion circuits 11 to 1n are input to the gate terminal of the common output transistor Vot1.

The reference circuit 21 surrounded by a broken line corresponds to the reference circuit 2 in FIG. 1, and such a reference circuit is provided for each of the reference sensors SR1 to SRn. Each reference circuit 2
1 to 2n are output from a common output transistor Vot.
2 is input to the gate terminal.

Each of the photoelectric conversion circuits 11 to 1n is sequentially turned on with a different timing so that the output switches SW1 to SWn are not simultaneously turned on, and the output transistor Vot1 is turned on.
Sequentially amplify and output the detection signals of the photoelectric conversion circuits 11 to 1n. Similarly, the reference circuits 21 to 2n are sequentially turned on at different timings so that the output switches SWR1 to SWRn are not simultaneously turned on, and the output transistor Vot2 sequentially amplifies the output signals of the reference circuits 21 to 2n. And output. At this time, based on the correspondence between the reading sensor and the reference sensor, the output switch SW of the photoelectric conversion circuit is used.
By turning on i (i = 1 to n) and the output switch SWRi of the corresponding reference circuit at the same timing, dark correction can be performed by analog difference calculation in the differential circuit 3.

According to the present embodiment, in a photoelectric conversion device including a plurality of photoelectric conversion circuits and a plurality of reference circuits,
The difference between the output voltage of the reading sensor S1 and the output voltage of the reference sensor SR1 corresponding to its dark output can be obtained even with the use of fewer output transistors and an A / D conversion circuit. Becomes possible. Further, the temperature change of the reading sensor S1 can be canceled by taking the difference.

Embodiment 3 In this embodiment, a photoelectric conversion device including a plurality of photoelectric conversion circuits and a smaller number of reference circuits than the photoelectric conversion circuits will be described. FIG. 4 is a diagram showing a configuration example of a photoelectric conversion device according to the present invention, in which n (n is 2 or more) reading sensors S1 to Sn are linearly arranged, and m (m <n) reading sensors are arranged. FIG. 3 is a diagram showing a state where reference sensors SR1 to SRm are linearly arranged near each reading sensor. The circuit diagram of Embodiment 2 is the same as that of Embodiment 2 except that m photoelectric conversion circuits 11 to 1n are provided with m reference circuits 21 to 2m.
This is the same as the case of FIG.

As in the case of the second embodiment, the photoelectric conversion circuits 11 to 1n are sequentially turned on at different timings so that the output switches SW1 to SWn are not simultaneously turned on.
Then, the detection signals are sequentially output. On the other hand, the reference circuits 21 to 21
2m outputs a plurality of times as needed, and turns on SWR1 to SWRm so that the total number of outputs is n.
I do. Each output of the reference circuits 21 to 2m is connected to the photoelectric conversion circuit 1
This is performed in synchronization with the output timings 1 to 1n.

FIG. 5 shows the output timings of the photoelectric conversion circuits 11 to 16 when n = 6 and m = 2, and the reference circuits 21 and 2
FIG. 4 is a diagram showing an example of an output timing of No. 2; In this case, the reference circuits 21 and 22 may be output three times each. That is, at the same timing as the output switches SW1 to SW3 of the photoelectric conversion circuits 11 to 13, the reference circuit 2
1 is turned on, and the photoelectric conversion circuit 14 is turned on.
The output switch SWR2 of the reference circuit 22 may be turned on at the same timing as that of the output switches SW4 to SW6.

The output transistor Vot1 is common to the photoelectric conversion circuits 11 to 16, and the output transistor Vot2 is
Since it is common to the reference circuits 21 and 22, if the output voltage difference between the output transistors Vot1 and Vot2 is obtained in the differential circuit 3, the dark correction can be performed for each of the reading sensors S1 to S6. The temperature change in S6 can also be offset.

According to this embodiment, the number m of reference sensors can be made smaller than the number n of reading sensors while performing dark correction and temperature correction. Therefore, the size of the photoelectric conversion device itself can be reduced.

Embodiment 4 FIG. In this embodiment, the number and arrangement of reference circuits in the photoelectric conversion device of Embodiment 3 will be further described. FIG. 6 is an explanatory diagram relating to the variation of the dark output. (A) in the figure shows an arrangement example of 96 reading sensors S1 to S96 and two reference sensors SR1 and SR2, and (b).
FIG. 4 is a diagram showing a relationship between a position of a reading sensor and a variation of a dark output signal.

(B) shows that there is a variation of ΔV between the dark output signals of the reading sensors S1 and S96.
When the number of the reference sensors is one (only SR1), the outputs of all the reading sensors S1 to S96 are dark-corrected by the output of the same reference sensor SR1, and the influence of the variation ΔV of the dark output between the reading sensors S1 and S96 is reduced. It cannot be reduced. Therefore, the signal after the dark correction, that is, the output signal of the differential circuit 3 includes an error based on the variation ΔV of the dark output.

However, the two reference sensors SR1, SR
2 are arranged substantially evenly on the reading sensors S1 to S96, the maximum dark output variation is ΔV / 2. Therefore, the output signals of the reading sensors S1 to S48 are corrected by the output of the reference sensor SR1, and the reading sensor S49 is corrected by the output of the reference sensor SR2.
Correcting the output signals of steps S96 to S96 is equivalent to reducing the dark output variation to ΔV / 2 as a whole. That is,
Increasing the number of reference sensors can reduce the influence of dark output variations. However, the increase in the number of reference sensors increases the circuit scale of the entire photoelectric conversion device, so that the reduction in the variation in dark output and the reduction in the circuit scale are in conflict.

FIG. 7 shows a case where the ratio (circuit ratio) of the number n of photoelectric conversion circuits to the number m of reference circuits is changed.
FIG. 4 is a diagram illustrating an example of a dark output variation and a change in circuit scale. The logarithm of the circuit ratio n / m is plotted on the horizontal axis, the circuit scale is plotted with white circles (丸), and the dark output variation is plotted with black circles (●). Note that this is an example in which the reading sensors are arranged in a line in a straight line, and the reference sensors are arranged in the vicinity thereof at equal intervals.

In this figure, when the circuit ratio is 1, the circuit scale is maximized and the dark output variation is minimized.
When the circuit ratio becomes 10 or more, the circuit scale tends to be saturated. On the other hand, the dark output variation continues to increase. For this reason, it can be seen that when the circuit ratio is 10 or more, preferably, when the circuit ratio is 10 or more and 50 or less, the circuit scale and the dark output variation are compatible. At least two or more reference sensors may be arranged within this range. With this configuration, for example, by arranging 2 to 8 reference sensors, it is possible to correspond to a photoelectric conversion device having 20 to 400 reading sensors.

Embodiment 5 FIG. In the present embodiment, a structure for shielding the light receiving portion of the reference sensor from light will be described. FIG. 8 is a diagram illustrating an example of the arrangement of the reading sensors and the reference sensors, and includes n reading sensors S1 to Sn.
Are arranged in a line in a substantially straight line, and n reference sensors SR1 to SRn are arranged in a line in a substantially straight line so as to be parallel thereto. Further, the corresponding reading sensor Si and reference sensor SRi are arranged so as to be close to each other (i = 1 to
n).

The reading sensor and the reference sensor are provided as one semiconductor chip. By masking only the reference sensors SR1 to SRn by forming a light shielding film on the surface of the semiconductor chip where the reference sensors SR1 to SRn are arranged. be able to. Note that, in the present embodiment, the case of Embodiment 2 has been described as an example, but it goes without saying that the present invention can be similarly applied to other embodiments.

Embodiment 6 FIG. In this embodiment mode, a photoelectric conversion device which can obtain a dark output without using a light-shielding film by controlling operation timing of a reference circuit will be described. FIG. 9 is a timing chart illustrating an example of the operation of the photoelectric conversion device according to the present invention. In a photoelectric conversion device including n photoelectric conversion circuits and n reference circuits, an initialization switch of each photoelectric conversion circuit is provided. The operation of ASW1 to ASWn and output switches SW1 to SWn, the initialization switches ASWR1 to ASWRn of each reference circuit, and the output switches SWR1 to SWRn are shown.

In this figure, the output switch SW of the reference circuit
R1 to SWRn are output switches SW1 of the photoelectric conversion circuit.
To SWn, but the initialization switches ASWR1 to ASWRn of the reference circuit are not synchronized to the initialization switches ASW1 to ASWn of the photoelectric conversion circuit.

First, the operation of the photoelectric conversion circuit 11 will be described. A reset voltage is applied to the reading sensor S1 while the initialization switch ASW1 is at a high level. Thereafter, a period until the output switch SW1 becomes high level is an accumulation period (photoelectric conversion period) tc in which charges corresponding to the light intensity are accumulated in the reading sensor S1. The accumulated charge is output to the output transistor Vot1 as a detection signal while the output switch SW1 is at a high level. Similarly, initialization, accumulation, and output of the photoelectric conversion circuits 12 to 1n are sequentially performed so that the output periods do not overlap.

Next, the operation of the reference circuit 21 will be described. The output switch SWR1 is connected to the corresponding photoelectric conversion circuit 1
It changes to a high level at the same timing as the first output switch SW1. Therefore, the reference circuit 21 is the photoelectric conversion circuit 11
The signal is output at the same timing as. However, in the reference circuit 21, since the initialization switch ASWR1 changes to the high level immediately before the output switch SWR1 changes to the high level, the accumulation time (photoelectric conversion period) tcr of the initialization switch ASWR1 is
It is sufficiently shorter than the accumulation time tc of the photoelectric conversion circuit.

As described above, only the operation timing of the initialization switch is made different, and the accumulation time tcr of the reference circuit is extremely shortened, so that the dark output is equalized without shading the light receiving portion of the reference sensor. Then, the dark correction operation can be performed. For example, the accumulation time tcr of the reference circuit is
What is necessary is just to shorten it to about 0.01% or less of the accumulation time tc.

According to the present embodiment, since a dark output can be obtained without using a light-shielding film, the number of steps for manufacturing the photoelectric conversion device can be reduced by one. In addition, since a problem due to a shift in the formation position of the light shielding film does not occur,
The yield can be improved. Note that, in the present embodiment, the case of Embodiment 2 has been described as an example, but it goes without saying that the present invention can be similarly applied to other embodiments.

Embodiment 7 FIG. In this embodiment, a photoelectric conversion device that performs a difference calculation of a current signal using a current mirror circuit will be described. FIG. 10 is a diagram showing a configuration example of the photoelectric conversion device according to the present invention. In the figure, 11 is a photoelectric conversion circuit, 21 is a reference circuit, 31 is a correction circuit, and A is an amplifier. When this photoelectric conversion device includes a plurality of sets of photoelectric conversion circuits, reference circuits, and correction circuits, the output switches SW1, SW2,... Of each photoelectric conversion circuit are input to a common amplifier A.

In the photoelectric conversion circuit 11, the voltage signal from the photodiode sensor S1 is converted into a current signal by the transistor TR1 as a voltage / current conversion means, and a part thereof is inputted to a current mirror circuit comprising the transistors TRa and TRb. You. The transistor TRc is a diode-connected current-voltage converter, and converts the current signal of the current mirror circuit into a voltage signal. C1 is a storage capacitor, which stores charges based on the output voltage of the transistor TRc when the storage switch SWc is ON, and outputs a voltage signal to the amplifier A when the output switch SW1 is ON.

FIG. 11 is a timing chart showing an example of the operation of the photoelectric conversion circuit 11. When the reset switch ASW1 is turned on to apply a reset voltage to the reading sensor S1, and then the initialization switch ASW1 is turned off and light is irradiated to the reading sensor S1, a photoelectric effect occurs, and the gate voltage of the transistor TR1 fluctuates.

The transistor TR1 changes the drain current in accordance with the change in the gate voltage, and supplies a current to the diode-connected transistor TRa. Since the transistor TRa and the transistor TRb have a common gate and are current mirror connected, the current flowing between the drain and the source of the transistor TRa and the transistor TRb
The current flowing between the drain and the source becomes equal.

The current flowing through the transistor TRb is converted into a current by the diode-connected transistor TRc, and is stored as a voltage in the storage capacitor C1 via the storage switch SWc which is turned on before light irradiation. By turning off the accumulation switch SWc after the elapse of the accumulation period, the capacitor C1 is disconnected from the transistor TRc, and by turning on the output switch SW1, the voltage held in the accumulation capacitor C1 is output to the amplifier A.

When there are a plurality of such photoelectric conversion circuits, the output switches SW1, SW2,... Of each photoelectric conversion circuit are sequentially turned on, so that the common amplifier A and the A / D conversion circuit 4 The detection signal of each photoelectric conversion circuit can be output to the digital processing circuit 5.

The reference circuit 21 includes a light-shielded photodiode sensor SR1, an initialization switch ASWR1, and a transistor TRR1 as voltage-current conversion means. The initialization switch ASWR1 operates at the same timing as the initialization switch ASW1 of the photoelectric conversion circuit 11, and the transistor TRR1 converts a voltage signal (dark output) generated by the reference sensor SR1 into a current signal and outputs the current signal to the correction circuit 3. I do.

The correction circuit 31 includes transistors TRx1,
It has a current mirror connection of TRy1 and has a photoelectric conversion circuit 1
Subtract the current value of the reference circuit 2 from the current value of 1.
It is connected to the photoelectric conversion circuit 11 and the reference circuit 21. That is, a current mirror circuit configured by connecting the gate terminal of the diode-connected transistor TRx1 and the gate terminal of the transistor TRy1 is provided, and the current signal of the reference circuit 21 flows into the drain terminal of the transistor TRx1. A current having the same current value flows from the photoelectric conversion circuit 11 to the drain terminal of the transistor TRy. Therefore, the difference between the output currents of the transistors TR1 and TRR1 is input to the current mirror circuits TRa and TRb.

In the present embodiment, the output signals of the reading sensor S1 and the reference sensor SR1, which are voltage signals, are converted into current signals, and dark correction processing is performed as a difference calculation of the current signals. In this way, by handling the output signal at the time of dark correction with a current, the operating speed can be increased and the reading time of the photoelectric conversion device can be reduced as compared with the case of handling with a voltage.

Embodiment 8 FIG. In the present embodiment, a case will be described where dark correction of two or more reading sensors is performed using one reference sensor in the photoelectric conversion device of the seventh embodiment. FIG. 12 is a diagram showing a configuration example of the photoelectric conversion device according to the present invention. In the figure, 11, 12, 13, 14 ... are photoelectric conversion circuits, 21, 22
... are reference circuits, and 31 and 32 are correction circuits. One reference circuit and one correction circuit are arranged for two photoelectric conversion circuits.

The initialization switches ASW1 and ASW2 of the photoelectric conversion circuits 11 and 12 are turned on and off at the same timing.
And the initialization switch ASWR of the corresponding reference circuit 11
1 is also turned on and off at the same timing. Since the reference sensor SR1 is shielded from light, a dark-level drain current flows through the transistor Trx1 after the initialization switch ASWR1 is turned off.

Here, the two photoelectric conversion circuits 11 and 12
One reference circuit 21 (one-pixel reference sensor SR1) is arranged for (two-pixel reading sensors S1, S2). Therefore, the current flowing through the transistor TRy1 is
The dark level current of the reference sensor SR1 (that is, TRx1
Of the transistor TR so as to be about twice the drain current of the transistor TR.
If the current amplification factor of y1 is set, the reading sensors S1, S2
From the drain currents of the transistors TR1 and TR2 through which the bright level current flows, the dark currents IMS1 and IMS2 respectively.
(IMS1 = IMS2) can be subtracted to perform dark correction.

FIG. 13 is a diagram showing another configuration example of the photoelectric conversion device according to the present invention. In this photoelectric conversion device, one reference circuit is arranged for four photoelectric conversion circuits. When one pixel of the reference sensor is arranged for every four pixels of the reading sensor, the current mirror-connected transistor TRy
1 is set to four times the current amplification factor of the transistor TRx1, the drain currents of the transistors (not shown) through which the light-level currents of the photoelectric conversion circuits 11 to 14 flow are calculated from IMS1 to IMS4 (IMS1 = IMS2 = IMS3). =
IMS 4) can be subtracted to perform dark correction.

That is, by setting the current amplification factors of the transistors TRy1, TRy2,... Of the correction circuits 31, 32,... According to the ratio of the reading sensor to the corresponding reference sensor, the dark correction operation becomes possible. .

According to the present embodiment, one reference circuit and one correction circuit are arranged corresponding to a plurality of photoelectric conversion circuits,
By determining the current amplification factor of the current mirror connected transistor in the correction circuit from the ratio between the reference circuit and the photoelectric conversion circuit, dark correction can be performed using a small number of reference circuits.

Embodiment 9 In this embodiment, the number and arrangement of reference circuits in the photoelectric conversion device in Embodiment 8 will be further described. FIG. 14 is a diagram illustrating an example of a dark output variation and a change in circuit scale when the ratio (circuit ratio) of the number n of photoelectric conversion circuits to the number m of reference circuits is changed. The logarithm of the circuit ratio n / m is plotted on the horizontal axis, the circuit scale is plotted with white circles (丸), and the dark output variation is plotted with black circles (●). Note that this is an example in which the reading sensors are arranged in a line in a straight line, and the reference sensors are arranged in the vicinity thereof at equal intervals.

In this figure, when the circuit ratio is 1, the circuit scale is maximized and the dark output variation is minimized.
Then, as the circuit scale increases, the dark output variation increases, while the circuit scale saturates at a circuit ratio of 8 or more,
When the circuit ratio is 4, it tends to decrease to about 50%. Therefore, when the circuit ratio is 4 or more, preferably 4
It can be seen that the circuit scale and the dark output variation are compatible when the number is 16 or less. That is, the photoelectric conversion sensors 4 to 16
It is sufficient to arrange one pixel of the reference sensor for each pixel.

[0068]

The photoelectric conversion device according to the present invention includes a correction circuit for correcting the darkness of the detection signal of the photoelectric conversion circuit based on the detection signal of the reference circuit, so that the dark output variation can be corrected. Further, since the temperature change of the dark output is offset, the image quality can be maintained.

Further, in the photoelectric conversion device according to the present invention, the number of reference pixels is smaller than that of two or more photoelectric conversion elements, so that the photoelectric conversion device (chip size in the case of a semiconductor device) can be reduced in size and the yield can be improved. be able to.

Further, the photoelectric conversion device according to the present invention
By disposing the reference circuit for each of the 50 or less photoelectric conversion circuits, it is possible to achieve both the dark output variation and the circuit scale.

Further, in the photoelectric conversion device according to the present invention, by making the photoelectric conversion period of the reference circuit shorter than the photoelectric conversion period of the photoelectric conversion circuit, the step of shielding the reference pixel from light can be reduced. In addition, since a problem due to a displacement of the light-shielding film does not occur, the yield can be improved.

Further, the photoelectric conversion device according to the present invention performs dark correction based on the difference between the current signals of the photoelectric conversion circuit and the reference circuit, so that the operation speed can be increased and the reading time of the photoelectric conversion device can be reduced. I can do it.

Further, in the photoelectric conversion device according to the present invention, by arranging the reference circuit for every 4 to 16 photoelectric conversion circuits, it is possible to achieve both the dark output variation and the circuit scale.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a photoelectric conversion device according to the present invention. (Embodiment 1)

FIG. 2 is a diagram illustrating a configuration example of a photoelectric conversion device according to the present invention, and is a diagram illustrating an arrangement of a reading sensor and a reference sensor. (Embodiment 2)

FIG. 3 is a diagram illustrating a circuit configuration example of the photoelectric conversion device illustrated in FIG. 2;

FIG. 4 is a diagram illustrating a configuration example of a photoelectric conversion device according to the present invention, and is a diagram illustrating an arrangement of a reading sensor and fewer reference sensors; (Embodiment 3)

FIG. 5 is a diagram illustrating an example of output timings of six photoelectric conversion circuits and two corresponding reference circuits.

FIG. 6 is an explanatory diagram relating to a variation in dark output;
(A) shows an example of the arrangement of a reading sensor and a reference sensor, and (b) is a diagram showing the relationship between the position of the reading sensor and the variation of the dark output signal. (Embodiment 4)

FIG. 7 is a diagram showing an example of a dark output variation and a change in circuit scale when the ratio of the photoelectric conversion circuit to the reference circuit is changed.

FIG. 8 is a diagram illustrating an example of a reference sensor in which a light receiving unit is shielded from light. (Embodiment 5)

FIG. 9 is a timing chart showing an example of the operation of the photoelectric conversion device according to the present invention without using a light-shielding film. (Embodiment 6)

FIG. 10 is a diagram illustrating a configuration example of a photoelectric conversion device according to the present invention using a current mirror circuit. (Embodiment 7)

11 is a timing chart showing an example of the operation of the photoelectric conversion circuit 1 shown in FIG.

FIG. 12 is a diagram illustrating a configuration example of a photoelectric conversion device according to the present invention using a current mirror circuit and including fewer reference sensors than reading sensors. (Embodiment 8)

FIG. 13 is a diagram showing another configuration example of the photoelectric conversion device according to the present invention.

FIG. 14 is a diagram showing an example of a dark output variation and a change in circuit scale when the ratio of the photoelectric conversion circuit to the reference circuit is changed in the photoelectric conversion device according to the present invention using the current mirror circuit. (Embodiment 9)

FIG. 15 is a diagram showing a configuration of a conventional photoelectric conversion device.

FIG. 16 is a diagram showing an example of a temperature-dark output characteristic of a photodiode sensor.

FIG. 17 is a diagram showing an example of a detection signal at different temperatures T0 and T1.

[Explanation of symbols]

11 to 1n Photoelectric conversion circuits S1 to Sn First photodiodes (reading sensors) ASW1 to ASWn Initialization switches SW1 to SWn Output switches 21 to 2n Reference circuits SR1 to SRn Second photodiodes (reference sensors) ASWR1 to ASWRn Initial Switch SWR1 to SWRn output switch 31 to 3n correction circuit 4 A / D conversion circuit 5 digital processing circuit

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/028 H04N 1/04-1/207

Claims (7)

(57) [Claims] 1. A first photodiode for photoelectrically converting irradiation light to generate a detection signal, and the first photodiode
And a second photoelectric conversion circuit having substantially the same characteristics as the first photodiode.
Photodiode, the second photodiode
And second switch means for resetting the first and second switches.
The operation timing of the switch means is changed, and the second photo
The photoelectric conversion period of the diode is
A reference circuit that generates a detection signal of the photoelectric conversion circuit when non-irradiation is equivalently performed by making the period shorter than the photoelectric conversion period, and a correction that performs dark correction of the detection signal of the photoelectric conversion circuit based on the detection signal of the reference circuit. A photoelectric conversion device comprising a circuit. 2. The circuit according to claim 1, wherein the correction circuit includes a differential circuit to which a detection signal of the photoelectric conversion circuit and a detection signal of the reference circuit are input, and the photoelectric conversion circuit and the reference circuit output the detection signal in synchronization. 3. The photoelectric conversion device according to claim 1. 3. A photoelectric conversion apparatus comprising two or more photoelectric conversion circuits having different output timings of detection signals, wherein the correction circuit sequentially performs dark correction of detection signals of the photoelectric conversion circuits based on detection signals of the reference circuit. The photoelectric conversion device according to claim 1 . 4. a plurality of the photoelectric conversion circuit, the first photodiode is arranged substantially linearly, claim 3 to place the reference circuit for each photoelectric converter 10 or more 50 or less
3. The photoelectric conversion device according to claim 1. 5. The photoelectric conversion circuit and the reference circuit generate a detection signal as a current signal, and the correction circuit outputs a current value equal to the current signal of the reference circuit from the current signal of the photoelectric conversion circuit via a current mirror circuit. claims 1 to subtract 4
The photoelectric conversion device according to any one of the above. 6. A photoelectric conversion apparatus comprising two or more photoelectric conversion circuits having different detection signal output timings, wherein the correction circuit amplifies a current signal from one reference circuit and subtracts it from the current signals of the two or more photoelectric conversion circuits. The photoelectric conversion device according to claim 5 . 7. The photoelectric conversion device according to claim 6 , wherein a plurality of the photoelectric conversion circuits are provided, the first photodiodes are arranged substantially linearly, and the reference circuit is arranged for every 4 to 16 photoelectric conversion circuits. apparatus.