JPS5967770A - optical reader - Google Patents

Abstract

PURPOSE:To attain high speed signal readout, by decreasing the number of switching times of a switch required for one scanning to less than conventional circuits by 1/10 or more with a signal readout from a common electrode so as to eliminate the effect of a matrix multi-layer wiring which is a cause for parasitic capacitance. CONSTITUTION:Analog switches 20-27, 28-35 are scanned with an individual electrode scanning circuit 44 and a common electrode scanning circuit 45, a signal charge stored at each picture element is converted into a voltage by using a preamplifier 14 and an integrator 16 and outputted through a sample-and-hold circuit (S/H) 18. Further, an analog switch 15 to reset the charge stored in the parasitic capacitance of the common electrode at the switching of the analog switches 28-35 at the common electrode side is connected to an input terminal of the preamplifier 14 so as to prevent the saturation of the preamplifier. Since the parasitic capacitance of the common electrode without any multi-layer wiring is very small in comparison with that of the individual wiring, spike noise is reduced. Since the switching of the analog switches 28-35 has only to be done at each common electrode, the number of times of switching is remarkably reduced.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is applied to an optical reading device used in a facsimile machine or a character reading device, and is particularly applied to an optical reading device that reads a document in close contact with it [Prior art] ] FIG. 1 shows the general configuration of a contact reading type optical reading device (line sensor) to which the present invention is applied.

The written image on the paper surface moving in the direction of arrow 6 (sub-scanning direction) reflects light from the light source 4, and is converted into an electrical signal by the light receiving section 2 of the line sensor 1 via the lens array 3.

FIG. 2 is a circuit diagram of an optical reading device previously invented by the present inventors. Here, 8 is a separation diode, and 9 is a photodiode, forming the light receiving section 2. 1o is a block common electrode scanning circuit, which has a voltage V that can bias the separation diode in the positive direction when selecting a pixel;
is grounded when not selected. Reference numeral 11 denotes an individual electrode scanning switch, which connects the signal line of the sensor to the preamplifier 14 when selected, and connects to a voltage source 12 (voltage Vb) for reverse biasing the separation diode when not selected.

At the input terminal of the preamplifier, there is a sensor parasitic capacitance of 13°13',
13" and a reset switch 15 for discharging the reverse bias voltage accumulated in the parasitic capacitance of the switch 11 and short-circuiting the switching noise of the switch 11. A spike-like current output is provided at the output end of the preamplifier. An integrating circuit 16 for integration is connected.The operation of the optical reading device shown in FIG. 2 will be explained using the timing chart shown in FIG. 3.First, at time t1, the switch 11 on the individual electrode side is switched.t1 ~t3, reset switch 1
5 is closed to discharge the reverse bias voltage accumulated in the individual electrode parasitic capacitances 13 and 13' of X and the switch parasitic capacitance of XI. At that time, a bias voltage is applied to the common electrode Y at the output 1 to t4. Accordingly, when the YI voltage rises, a positive charge Q, shown in Figure 2, enters the preamplifier, and when the Y+ voltage falls, a negative charge Q- enters the preamplifier. This is integrator 16
is integrated, and becomes the output voltage v0. The signal voltage is 14~
obtained at time t. At t, the reset switch 15 is short-circuited again to short-circuit the switching noise at the time of the next switch change. Here, the time required to read one pixel is t,%t.

When used in high-speed facsimile, the required reading time for one pixel is 2 μs or less. In the device shown in FIG. 2, the time required to prevent switching noise and discharge parasitic capacitance is 1.
~[, and t1 to t, require approximately 1 μs. This is due to the sensor parasitic capacitance IJ13' caused by the wiring intersections of the two-layer wiring of the matrix.
This is because the capacitance of the capacitor 121 has a large value of several hundred pF, and the parasitic capacitance of the scanning switch is also large, several tens of pF. If a field-effect MO8 solid-state switch with low on-resistance is used for 11 for the purpose of switching, the coupling capacitance between the gate electrode to which the control signal is applied and the source and drain through which the signal passes increases, resulting in increased switching noise. ,1
It cannot be canceled in about μs. As described above, it is difficult to increase the speed of signal readout with the optical reading device having the configuration shown in FIG.

[Purpose of the invention]

An object of the present invention is to improve the optical reading device using the matrix driving method as shown in FIG. 2 and to provide an optical reading device capable of high-speed signal reading.

[Summary of the invention]

In order to achieve the above object, the present invention reads out signals from the common electrode side, thereby reducing the number of switching times required for one scan by more than one order of magnitude compared to the conventional method, and reducing the number of switching times required for one scan by more than one order of magnitude compared to the conventional method. By removing the influence, an optical reading device that can read signals at high speed and has few noise components is realized.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail using examples.

A first embodiment of the present invention will be described in detail using FIGS. 4, 5, and 6.

FIG. 4 shows the circuit configuration of an embodiment of the optical reading device according to the invention, and FIGS. 5 and 6 are time charts and operation principle diagrams for explaining its operation. Note that in order to avoid complexity of explanation, a 4×4 matrix structure is used.

In FIG. 4, the anode side of the separation diode 8 is connected to the individual electrodes Y, ~Y4, and the anode side of the photodiode 9 (or a photoconductive capacitor) is connected to the common electrodes X, ~Y4.
X4, and analog switches 20 to 27.
It is connected to the target voltage source 19 or ground, the bias voltage source 12 or the preamplifier input terminal via 28 to 35. These analog switches 20~27゜2
8 to 35 are scanned by an individual electrode scanning circuit 44 and a common electrode scanning circuit 45, respectively, and the signal charge accumulated for each pixel is converted into a voltage using a preamplifier 14 and an integrator 16, and a sample hold circuit (8/H ) 18.

Further, when the analog switches 28 to 35 on the common electrode side are switched, an analog switch 15 is connected to the input terminal of the preamplifier 14 to reset the charge accumulated in the parasitic capacitance of the common electrode, thereby preventing saturation of the preamplifier. I'm here. These individual electrode scanning circuits 44 and common electrode scanning circuits 4
5. The integrator 16, the S/I circuit 18, and the parasitic capacitance reset analog switch 15 are controlled by the control signal generation circuit 46.

In FIG. 5, Y+ to Y, , XI-X indicate changes in the voltage applied to the individual electrodes and the common electrode, respectively. A target voltage source (VT) 19 is connected to the individual electrode of the pixel to be read, and a preamplifier input terminal is connected to the common electrode. That is, the state is shown in FIG. 6(a). The preamplifier 14 has a low input impedance, and its input terminal can be considered to be virtually grounded. As a result, the isolation diode 8 is biased in the forward direction, and a charge equal to the charge Qs flowing through the photodiode 9 during the accumulation period is injected into the cathode side of the isolation diode 8. At this time, the preamplifier 14 has a charge Qs
A positive charge Q, which is obtained by adding a certain offset to Q, enters and is integrated by an integrator 16. Subsequently, the individual electrodes are grounded, resulting in the state shown in FIG. 6(b). At this time, negative offset charges -Q- enter the preamplifier, and these offsets are canceled by the integrator 16, and the signal charge Q+5 (
=Q, a pressure proportional to -Ql is generated at the output end.

Pixels that are not read out are shown in (b) to (d) in Figure 6.
It will be in one of the following states. (C) In (d), if the bias 'rli pressure Vm'i is set to 1/2- of the target ridge pressure Vt, the difference between the voltages applied to both electrodes will both be V r /2. Therefore 0))~(
In state d), a condition can be created in which both diodes are reverse biased. In other words, information about the light amount accumulation of that pixel is saved.

In Fig. 5, analog switches 28 to 35 on the common electrode side
Along with the switching operation, spike-like noise occurs in the output of the preamplifier. The cause of this is the parasitic capacitance of the common electrode and the analog switches 28 to 35, as described above. However, since the parasitic capacitance of the common electrode without the multilayer wiring section is extremely small compared to the individual wiring side, spike noise can be reduced. 1. As is clear from a comparison with FIG. 3, it is not necessary to switch the analog switches 28 to 35 on the common electrode side for each pixel, but it is sufficient to switch the analog switches 28 to 35 for each common electrode.

Therefore, for example, an A4 size light receiving element (1728
pixel), the number of common electrodes and individual electrodes is 32 and 54, respectively.
In the case of books, the number of switching required for one scan can be reduced to 1154
This makes it possible to reduce this to 32 times. therefore,
The time required to reset the preamplifier is also 115 times longer than the conventional one.
4, and a high-speed read operation can be realized.

1. Even if an analog switch with a relatively slow switching speed for driving the liquid crystal is used on the common electrode side, the number of switching is small, so it cannot be a factor that increases the reading time required for one scan.

Therefore, the cost of the scanning circuit system can be significantly reduced.

Next, a second embodiment of the present invention will be described.

FIG. 7 shows the configuration of a light receiving element and a driving circuit of an embodiment of the optical reading device according to the present invention, and FIG. 8 is a principle diagram for explaining its operation.

Using FIG. 7, the explanation will focus on all the differences from the first embodiment. A photoconductive capacitor 9' is connected to the cathode of the separation diode 8 and stores the light 7 [L current] during the storage period. ! ! The individual electrodes Y1 to Y4 are directly driven by the individual '11L pole scanning circuit 44. The time chart for driving this light receiving element is the same as that shown in FIG.

FIG. 8 is a diagram showing the operating principle of this embodiment. When reading a signal, the state is a), and at other times, the state is any one of b) to d). In the first embodiment, the bias city is placed in the state shown in FIG. 6 d).
Pressure v! When the value of l becomes large, the photodiode 9 is biased in the forward direction, and the information of that pixel is lost. In contrast, in this embodiment, the photoconductive capacitor 9' is used instead of a photodiode, so the above-mentioned drawback is not present. In other words, even if the bias width and voltage VB are close to or higher than the target voltage VT, pixel information is preserved, so the saturation level regarding the amount of light can be increased. .

It is clear that the same effect can be obtained by using a photodiode instead of the isolation diode 8 and by using a simple capacitor instead of the photoconductive capacitor 9'.

Next, a third example will be described. FIG. 9 is a configuration diagram thereof, and FIG. 10 is a timing chart for explaining the operation. In order to simplify the explanation, a light receiving element with six individual electrodes and six common electrodes and 18 pixels will be used, and the differences from the two embodiments described above will be mainly described.

In FIG. 9, three sets of pixel arrays connected to the individual electrodes YI''Ys are divided into the first half and the second half, common electrodes X1 to X6 are provided to these, and an individual electrode scanning circuit 44 and a common electrode scanning circuit 45 are provided. By driving, a full voltage as shown in FIG. 10 is applied.A mere capacitor 9'' is connected to the photodiode B11 and the common electrode XI-Xs to the individual electrodes Y, to Yg. Analog switches 50 to 61 are connected to the individual electrodes Xl to Xs, and bias voltage distribution sources 12 (■, l) or analog switches 62 to 6 are connected to the individual electrodes Xl to Xs.
5 to the preamplifier 14 input terminal (virtual ground) or ground. These analog switches are controlled by a control signal generation circuit 46.

A feature of this embodiment is that, for example, a signal readout operation for pixels belonging to the common electrode X and an idle reading operation for pixels belonging to the common electrode X1 can be performed simultaneously.

However, it is also possible to reset the parasitic capacitance I: of the common electrode X to be read next during the signal reading operation of the pixel belonging to the common electrode Xt.

All of these relationships will be explained using FIG. T1 in the diagram
During the period, the common '
11L pole X is grounded to reset the effects of parasitic capacitance. Next, in the period of r1 + Mayuzumi, X.

is the preamplifier 14 through analog switches 58 and 62.
Connect to the input terminal (virtual ground) of the individual electrodes Y4 to Y6
tl'L pressure VT is applied sequentially to As a result, a pulse waveform as shown in the figure is generated at the output terminal of the preamplifier 14, and a voltage proportional to the charge accumulated in each pixel is generated at the output of the integrator 16. Subsequently, during the period T1 to T6, the common electrode X! becomes grounded again, and target voltage VT is applied to individual electrodes X4 to XI at T4.

As a result, the photodiode 8' of each pixel is biased in the forward direction, and a sufficient idle reading operation is performed.

At the rear end of TsQ, the analog switch 59 is turned on, and a bias voltage Vm that reverse biases the photodiodes 8' is applied to the common electrode X, and each pixel shifts to a light amount accumulation state. During the period T3 to T6, the common electrode Xs is connected to the preamplifier 14, and signals from each pixel are read out in parallel.

In this way, the common electrode can be divided to perform signal readout operations,
By using a driving method in which the idle reading operation and the parasitic capacitance reset operation proceed simultaneously, it is possible to realize a light receiving element that has few harmful noise components and is capable of high-speed signal reading.

In this embodiment, a light receiving element composed of a photodiode 8' and a capacitor 9# was used, but a separation diode 8 and a photodiode 9, as well as a separation diode 8 and a photoconductive capacitor 9' as in the previous embodiment, were used. It is clear that the same effect can be obtained even when configured as follows. In order to further increase the speed, it is also possible to provide a preamplifier for each set of common 7% poles and operate them in parallel.

〔Effect of the invention〕

According to the present invention, by reading signals from the common electrode side of the light receiving element, the time required for switching switches, resetting parasitic capacitance, etc. can be significantly shortened, and high-speed signal reading is possible. . In fact, even if an analog switch for driving the liquid crystal, which has a relatively slow operating speed, is used, the reading speed does not decrease much, and the cost including the driving circuit can be significantly reduced.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a close reading type line sensor, Fig. 2 is a block diagram of a conventional matrix drive line sensor, Fig. 3 is a timing chart thereof, and Fig. 4 is a block diagram of a first embodiment of the present invention. , Figure 5 is the timing chart), @6
7 is a block diagram of the second embodiment of the present invention, FIG. 8 is a block diagram of the operating principle, FIG. 9 is a block diagram of the third embodiment of the present invention, and FIG. The figure is a timing chart. 1... Close reading line sensor, 2... Light receiving part,
3... Lens array, 4... Light source (LED etc.), 5
...Original, 6...Original scanning direction (sub-scanning direction), 7
...Main scanning direction, 8...Separation diode, 9...
Photodiode, 8′...Photodiode, 9′・
...Photoconductive capacitor, 9''...Capacitance, 10...Common electrode scanning circuit, 11...Switch for individual electrode scanning, 12
...Bias voltage source (VB), 13.13', 1
3N...Individual electrode parasitic capacitance, 14...Norian amplifier,
15... Reset switch, 16... Integrator, ■
. ...output current during readout, vo...integrator output voltage, QR...parasitic capacitance accumulated charge, Q...charge at rise, Q-...charge at fall, 18...sample Hold circuit, 19... target voltage source (■T),
20-27... Analog switch for individual electrode scanning, 2
8-35...Analog switch for common electrode scanning, 36
~43...Inverter, 44...Individual electrode scanning circuit, 45...Common electrode scanning circuit, 46...Control signal generation circuit, 50-61...Analog switch for common electrode scanning, 62-65 ...Analog switch for switching combinations,
66-73...Inverter. Figure 1 Atsushi Figure 5 Y4 and 4 C'lL in S/H out η 6th mouth <6) (+)) <C)
(Numaya to figure pt f static π exit θ Continuation of page 1 0 Author: Tetsuo Tajiri, Yokosuka Telecommunications Research Institute, Nippon Telegraph and Telephone Public Corporation, 1-2356 Takeshi, Yokosuka-shi, Japan) Applicant: Nippon Telegraph and Telephone Public Corporation

Claims (1)

[Claims] 1. A unit pixel in which a photodiode and a capacitor, a photoconductive film and a separation diode, or a photodiode and a separation diode whose rectifying direction is opposite to this are connected in series is arranged in one dimension, and these are arranged in one dimension. Divide into at least two consecutive groups, all the pixels of each group are connected to the corresponding common electrode, and the pixels in each group at the same position relative to the pixel arrangement are connected to h. In the one-dimensional light-receiving elements grouped into corresponding individual electrodes, a voltage that reverse biases the separation diode is applied to the group that does not perform signal reading, and a voltage that reverse biases the separation diode is applied to the group that performs signal reading, and the voltage is applied to the group that does not perform signal reading according to the pixel arrangement in each group. An optical reading device characterized in that a signal is read by sequentially applying a voltage that forward biases a separation diode or a photodiode to individual electrodes. 2. The optical reading device according to claim 1, further dividing the pixels belonging to the group into two or more groups,
In the light receiving element in which each group is provided with a common electrode, the common electrode of the group for reading out the signal is connected to the output circuit,
A signal readout operation is performed by sequentially applying a forward-biased voltage to each isolation diode or photodiode to the individual electrode, and the isolation diode or photodiode is located at the same position relative to the group,
For groups that do not perform readout, a voltage that causes the diodes to be reverse biased is applied to the common electrode, and for other groups, a voltage that causes all of the diodes to be reverse biased is applied to the common electrode and the individual electrodes. An optical reading device characterized in that it performs an idle reading operation in which a voltage is applied to both electrodes so that at least two of the diodes become forward biased at the same time.