JP2531071B2 - Image sensor drive - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for an image sensor, and more particularly to an S of a document information reading signal.
The present invention relates to an image sensor driving device with improved / N.

[0002]

2. Description of the Related Art An example of a conventional device of this type will be described with reference to FIG. As shown in the figure, the conventional driving device has M blocks of photocell parts B (1) to B (M) each of which is formed by N photocells and one terminal of each of the photocells. Switching elements 2 (1) to 2 (MN) connected to each other and N signal lines L (1) to L (N) commonly connecting the switching elements connected to the corresponding photodiodes of each block. , And an analog multiplexer 10 that accommodates the signal line. Further, the other terminals of the MN photocells are connected to the power supply voltage VB via a common line CL, and the switching elements are common gate lines G1 and G in block units.
2, ..., G (M).

As shown in FIG. 6, the analog multiplexer 10 includes a reset switch group 4 (1) composed of FETs connected between each of the signal lines L (1) to L (N) and ground. ) -4 (N) and a voltage follower type amplifier with high input impedance 3 (1) -3
(N) and switch groups 5 (1) to 5 (N) connected to the amplifiers 3 (1) to 3 (N) and controlled to be turned on and off by the output of the shift register 11. There is.

In the image sensor driving device having such a structure, the reflected light from the document is transferred from the photocell section B (1) to
When B (M) is irradiated, each photocell discharges the capacitors connected in parallel according to the amount of incident light, and converts the document information into the amount of accumulated charges.

Reset switch 4 at an appropriate timing
(1) to 4 (N) are turned on, and the signal lines L (1) to (N)
Are turned off after being reset, and then a gate voltage is applied to the gate line G1, the switching elements 2 (1) -2
(N) is turned on, and voltage information according to the amount of accumulated charge is transmitted to the signal lines L (1) to L (N). Next, the switches 5 (1) to
5 (N) is sequentially turned on by the shift register 11, and the signal lines L (1) to L (N) are sequentially connected to the output line OUTL. As a result, the original information of the photocells 1-N belonging to the first block B (1) is transferred to the amplifiers 3 (1) -3 (N).
Is amplified and read out.

When this reading is completed, the gate line G1 is next.
Voltage applied to the reset switch 4
After (1) to 4 (N) are turned on, the gate voltage is applied to the gate line G2. As a result, the switching elements 2 (1) to 2 (N) are turned off and 2 (N + 1) to 2
(2N) is turned on. For this reason, the document information detected in the second block B (2) of the photocell portion is the signal line L.
(1) to L (N). Then, similarly to the above, the analog multiplexer 10 sequentially outputs the output lines OUT.
L is read.

Thereafter, the same operation is performed, and the original information for one line detected by the photocells belonging to the remaining blocks is sequentially read out to the output line OUTL.

[0008]

The above-mentioned conventional technique has the following problems. As described above, the document information detected by the photocell is output to the output line OU.
When reading to the TL, the reading of the original information of the photocell of one block is completed, and before reading the original information of the photocell of the next block, the remaining original information of the previous block is read by the signal lines L (1) to L ( 6) for removal from N).
Reset switch 4 (1) -4 shown in FIG.
A reset signal is applied to the gate of (N), and the reset switches 4 (1) to 4 (N) are turned on.

However, the reset switch 4
When the (1) to 4 (N) are turned on and off, noise is induced from the switch, and the noise is generated by the signal lines L (1) to L (L).
Due to (N), there is a problem that the S / N of read document information is deteriorated.

The input signal level to the analog multiplexer 10 is 1 to 100 mV, and the amplifier 3
The gain of (1) to 3 (N) is expected to be 100 times. In this circuit, the variation in the offset for each amplifier is several tens of mV, and the gains are resistors r1 to r.
It varies by about ± 50% due to variations in the values of n and R1 to Rn. The conventional device has a problem that it is difficult to realize a good S / N from this point of view as well.

If the gain of 100 times that of the amplifier is not achieved by one stage of the amplifier but achieved by using two stages of the amplifier of 10 times, the influence of the variation of the resistance can be reduced. However, there was a problem that the offset of the amplifier could not be removed even in this way.

An object of the present invention is to eliminate the above-mentioned problems of the prior art, provide an image sensor driving device capable of reducing an offset voltage of an amplifier and realizing a good S / N. .

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a plurality of units arranged in parallel with each other at a short distance to which an image information signal detected by a light receiving element of an image sensor is supplied. Signal line, a reset switch for resetting the image information signal of each signal line, a first amplifier connected to each signal line, and a first amplifier for the first amplifier.
Second amplifier connected through the switch and the first capacitor, a third amplifier connected to the second amplifier through the second switch and the second capacitor, and the second amplifier A third switch and a third capacitor connected in parallel between the input terminal of the amplifier and the ground, and a fourth switch and a fourth capacitor connected in parallel between the input terminal of the third amplifier and the ground. And a condenser of
The gains of the first and second amplifiers are made larger than that of the third amplifier, and the first to fourth switches are turned on and then turned off, and then the reset switch is operated to operate the signal line. Reset the image information signal of
The feature is that the first and second switches are subsequently turned on.

[0014]

According to the present invention, when the first and second switches are turned on after the first to fourth switches are turned on, the offset voltage has a small gain while the required gain is maintained. Since only the amplifier's one,
The offset voltage can be made very small. Therefore, it is possible to improve the S / N of the read document information.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention.
In the figure, 12 (1), 12 (2), ..., 12 (N)
Is the first switch, 13 (1), 13 (2), ..., 13
(N) is a noise storage circuit connected to the first switch, 14 (1), 14 (2), ..., 14 (N) are connected to signal lines L (1) to L (N), respectively. The signal line L
A subtraction circuit for subtracting the noise signal held in the noise accumulation circuits 13 (1) to 13 (N) from the read image signal sent by (1) to L (N). In addition, reference numerals other than the above indicate the same as or equivalent to 6.

The operation of this embodiment will be described with reference to the time chart of FIG. Note that the reference numerals in FIG. 2 are given corresponding to those in FIG. 1, and FIG. 2 shows the waveform of the signal at the portion indicated by the same reference numeral in FIG.

First, a reset pulse RP is applied (time t1), and the reset switches 4 (1) to 4 (N) are turned on. Thereby, the signal lines L (1) to L (N)
The electrical signal remaining on the reset switch 4
It passes through (1) to 4 (N) and is released to the ground, and the signal line is reset. However, the reset switch 4 (1)
When the .about.4 (N) is turned on and off, noise is induced from this switch and gets on the signal lines L (1) to L (N).

Therefore, the gate pulse GP is applied to the first switches 12 (1) to 12 (N) connected to the signal lines L (1) to L (N) (time t2), and the first pulses are applied. The switches 12 (1) to 12 (N) are turned on. As a result, the noise is generated in each of the noise storage circuits 13 (1) to 13 (N).
Is held.

Next, the gate line G1 of the image sensor
When the gate voltage is applied to (see FIG. 5) (time t3)
Image signals are transferred from the photocells belonging to the first block B (1) to the signal lines L (1) to L (N). This image signal is superimposed on the noise induced on the signal lines L (1) to L (N) and subtracted by the subtraction circuits 14 (1) to 14
Enter in (N). The subtraction circuits 14 (1) to 14 (N)
From the input signal to the noise storage circuits 13 (1) -13
The noise accumulated in (N) is subtracted, and the amplifier 3
Output to (1) to 3 (N). Therefore, the amplifier 3
The input signals (1) to 3 (N) are only the document information signal from which the noise has been removed.

Next, from the shift register 11 to the switch 5
When the select signals S (1) to S (N) are sequentially supplied to (1) to 5 (N), the switches 5 (1) to 5 (N) are sequentially turned on and the amplifiers 3 (1) to 3 (1) to The document information signals amplified by 3 (N) are sequentially sent to the output line OUTL.

When the reading of the document information detected by the photocells belonging to the first block B (1) of the image sensor is completed in this way, the reset switches 4 (1) to 4 (1) ... Reset pulse R to 4 (N)
P is applied (time t5). As a result, the signal line L
The original information signal remaining in (1) to L (N) is discharged to the ground, and then the first switch 12 (1) to
The gate pulse GP is applied to 12 (N) (time t6
), Noise is stored in the noise storage circuits 13 (1) to 13 (N). Subsequently, when the gate voltage G2 is applied to the gate line G2 of the image sensor (time t7), the original information signal detected by the photocell belonging to the second block B (2) is transferred to the signal lines L (1) to L (1). Is transferred to L (N).

This original document information signal is input to the subtraction circuits 14 (1) to 14 (N) together with noise, but due to the noise output from the noise storage circuits 13 (1) to 13 (N), as described above, The noise is offset. Therefore, the original information signal containing no noise is output to the amplifiers 3 (1) to 3 (N).
To enter. Next, the switch 5 is switched by the select signals S (1) to S (N) output from the shift register 11.
(1) to 5 (N) are sequentially turned on, and the amplifier 3
The document information signals amplified in (1) to 3 (N) are sequentially sent to the output line OUTL. Hereinafter, the same operation is repeated.

As described above, according to this embodiment, the noise induced on the signal lines L (1) to L (N) when the reset switches 4 (1) to 4 (N) are turned on and off is reduced. Since it can be removed, the document information signal with a good S / N can be taken out.

In the above embodiment, the subtraction circuit 14
The output signals of (1) to 14 (N) are output to amplifiers 3 (1) to 3
Although the amplification is performed in (N), this amplifier is not always necessary and may be omitted. Next, a second embodiment of the present invention will be described with reference to FIG.

This embodiment is based on the amplifier 3 shown in FIG.
By reducing the offset of (1) to 3 (N),
The S / N ratio of the document information signal is improved, and the same or equivalent components in FIG. 3 as those in FIG. 6 are designated by the same reference numerals. Further, since the reduction of the offset of each of the amplifiers 3 (1) to 3 (N) is achieved by the same means, the amplifier 3 (1) will be described below as a representative.

In the present embodiment, as shown, for example, the first and second amplifiers 21 and 22 having a gain of 20 are used.
And a third amplifier 23 having a gain of 1, for example, a first analog switch 24 and a first analog switch 24 in which the output terminal of the first amplifier 21 and the non-inverting input terminal of the second amplifier 22 are connected in series. It is connected by a capacitor 25. Also, the second
The non-inverting input terminal of the amplifier 22 is grounded in parallel by the second analog switch 26 and the second capacitor 27.

Further, the second amplifier 22 and the third amplifier 2
The third non-inverting input terminal is connected to the third non-inverting input terminal via the third analog switch 28 and the third capacitor 29, and the non-inverting input terminal of the third amplifier 23 is the fourth analog switch 30. And is grounded in parallel by the fourth capacitor 31.

Next, the operation of this embodiment will be described with reference to FIG. FIG. 4 is a timing chart showing the ON / OFF operation timing of each of the analog switches described above.
First, the original information signal Vin read from the photocell is supplied to the signal line L (1) by applying a gate voltage to the gate of the image sensor as in the above. After that, the first to fourth analog switches 24, 26, 28
And 30 are turned on (time t1).

As a result, the first capacitor 25 and the third capacitor 29 are charged, and the capacitor 25,
The inter-terminal voltages Vc25 and Vc29 of 29 and the inter-terminal voltages Vc27 and Vc31 of the capacitors 27 and 31 are as follows. Vc25 = 20 (Vin + Vos1) Vc29 = 20 Vos2 Vc27 = Vc31 = 0 Here, Vosl and Vos2 represent offset voltages of the first amplifier 21 and the second amplifier 22, respectively.

Next, the analog switches 24, 26,
28 and 30 are turned off and the switch 4 (1) is turned on to discharge the electric charge accumulated in the signal line L (1) (time t2).

Then, the first and third analog switches 24 and 28 are turned on (time t3). First,
When the first analog switch 24 is turned on, the capacitors 25 and 27 are connected in series, and the voltages Vc25 ′ and Vc27 ′ applied to the capacitors 25 and 27 are connected.
Is a value obtained by adding a voltage obtained by evenly distributing the difference of the newly applied voltage 20Vos1 with respect to the initial voltage to the initial voltage, and is as follows. The potential at point A becomes equal to Vc27 '. here,
First and second capacitors 25 and 27, and third and fourth capacitors
Although the capacitors 29 and 31 have the same capacitance, they are not limited to this. Vc25 ′ = Vc25 + (20Vos1−Vc25) / 2 = 10Vin + 20Vos1 Vc27 ′ = VA = Vc27 + (20Vos1−Vc25) / 2 + Vos2 = −10Vin + Vos2 Further, the potential at the point B is as follows from the same idea. VB = Vc31 ′ = Vc31 + (20VA−Vc29) / 2 + Vos3 = −100Vin + Vos3 Here, Vos3 is the offset voltage of the third amplifier 23.

In this state, when the analog switch 5 (1) is turned on and the document information signal is taken out to the output line OUTL, the circuit of FIG. 3 outputs the signal appearing at the output line OUTL with respect to the input document information signal Vin. VC = -100Vin + Vos
It will be 3. That is, the first and second amplifiers 21 and 2
The offset voltages Vos1 and Vos2 of 2 are canceled, and only the offset voltage Vos3 of the third amplifier 23 appears on the output line OUTL. Moreover, the gain of the entire circuit can be increased 100 times.

As described above, according to the present embodiment, since the offset is only the offset of the third amplifier 23 having the gain of 1 in the final stage, the offset can be made very small. Further, since it has a gain of 100 times, it exerts a great effect when the light irradiating the document surface has a low light intensity or when a high speed operation is performed.

The second embodiment is intended to reduce the offset voltage of the amplifier, but the first embodiment and the second embodiment
It will be apparent to those skilled in the art that, when combined with the embodiments, it is possible to realize a driving device for an image sensor in which noise induced in a signal line due to switching is reduced and an offset of an amplifier is reduced.

[0035]

As is apparent from the above description, according to the present invention, it is possible to reduce only the offset voltage of the amplifier while maintaining the necessary gain and improve the S / N of the read manuscript information. .

[Brief description of drawings]

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

FIG. 2 is a time chart of signals of main parts of FIG.

FIG. 3 is a circuit diagram of a second embodiment of the present invention.

FIG. 4 is a time chart of signals of main parts of FIG.

FIG. 5 is a block diagram of a conventional image sensor driving device.

6 is a circuit diagram showing a specific example of the analog multiplexer of FIG.

[Explanation of symbols]

21, 22, 23 ... First, second and third amplifiers 24,
26, 28, 30 ... Analog switch, 25, 26, 2
9, 31 ... Capacitor, L (1) ... Signal line.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Nishihara 2274 Hongo, Ebina-shi, Kanagawa Fuji Zerox Co., Ltd. Ebina Works (56) References

Claims (1)

(57) [Claims] 1. Parallel to each other at a short distance to which an image information signal detected by a light receiving element of an image sensor is supplied.
A plurality of arranged signal lines and a reset switch for resetting the image information signal of each signal line.
A switch, a first amplifier connected to said signal lines, and a second amplifier connected via a first switch and a first capacitor to the amplifier of the first, to the second amplifier A third amplifier connected via a second switch and a second capacitor, a third switch and a third capacitor connected in parallel between the input terminal of the second amplifier and ground, A fourth switch and a fourth capacitor connected in parallel between the input terminal of the third amplifier and the ground, and the gain of the first and second amplifiers is greater than that of the third amplifier. In addition to increasing the size, the first to fourth switches are turned on and then turned off, and then the reset switch
To reset the image information signal of the signal line,
Subsequently, the image sensor driving device is characterized in that the first and second switches are turned on .