JPH04332255A - Ic for contact type image sensor - Google Patents

Abstract

PURPOSE:To reduce cost and to unnecessitate the securing of excess space for installing an external switch on the substrate by providing a switch inside for forcibly removing residual electron charge from the capacitor. CONSTITUTION:A switch 20 that opens at a timing of 'H' of clock pulse CLK is provided between an image signal output terminal (SIG terminal) 11 and a grand terminal. When action of a shift register group 4 is terminated, that is, when image signals to be output from photocells 1a-1e are all output from SIG terminal 11, a chip photo cell 9 is set into an open state. Then, the residual electron charge of the capacitor for shaping an image signal taken out from SIG terminal 11 into an integral waveform is forcibly removed by the function of switch 20. With this, installing a switch for removing residual electron charge outside is no longer necessary.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an IC for a contact type image sensor used, for example, as a reading section of an image scanner for reading image information.

0002

[Prior Art] Figure 5 shows a conventional contact type image sensor I.
It is a circuit diagram showing C. In the figure, 1a to 1e are photocells (for example, phototransistors) that output current (image signal) when light is detected, 2 is an electrode pad (power terminal VDD), and 3a to 3e are A channel select switch 4 connected to the current output section of each photocell 1a to 1e is activated by a start pulse SI (start signal), and sequentially selects the image signals output by each photocell 1a to 1e (in this example, 1a →1b→1c→1d→1e) through the common signal line 7 to the image signal output terminal (SI
G terminal) 11, turn each channel select switch 3a to 3e sequentially (3a → 3b → 3c in this example)
→ 3d → 3e) A group of shift registers that perform on/off control according to the cycle of the clock pulse CLK, 4a to 4f are shift registers, 5 is an electrode pad (start pulse SI input terminal) that inputs the start pulse SI, 6 is the clock This is an electrode pad (clock pulse CLK input terminal) into which pulse CLK is input.

8, after being activated by the start pulse SI, the shift register group 4 is in operation (shift register 4a
After inputting the start pulse SI, shift register 4
f until the start pulse SI is output)
A flip-flop that continuously outputs an "H" level signal, 9 is inserted on the signal line 7, and a chip select switch that becomes closed when it receives a "H" level signal from the flip-flop, 10 is a signal line 7 and electrode pad (
This switch is connected between ground terminals (GND) 12 and repeatedly opens and closes in response to changes in the level of the clock pulse CLK.

FIG. 6 shows the contact type image sensor IC shown in FIG.
This is a circuit diagram in which multiple units are connected in series, and in the figure, 1
4, 15, and 16 are ICs for contact type image sensors, and 17 is a capacitor (usually several dozen) that shapes the image signal into an integral waveform.
0 pF), and 18 is a switch for forcibly removing the residual charge of the capacitor 15.

Next, the operation will be explained.

First, the SI terminals 5 and CL are connected from the outside.
A start pulse SI and a clock pulse CLK are supplied to the shift register 4 via the K terminal 6. Here, Figure 7
As shown in , the start pulse SI is the clock pulse C
The period is twice that of LK, and shift register 4 of shift register group 4 is activated at the falling edge of clock pulse CLK.
taken into a.

Next, by taking in the start pulse SI, the shift register 4a is activated, and as a result,
Shift register 4a is channel select switch 3a
The image signal output from the photocell 1a is outputted from the SIG terminal 11 via the signal line 7 by keeping it in the closed state for one cycle of the clock pulse CLK, and then the channel select switch 3a is opened. At the same time, the captured start pulse SI is transferred to the shift register 4b.

Therefore, since the start pulse SI is taken in in the order of the shift registers 4b→4c→4d→4e, the image signals of the photocells 1b to 1e are sequentially outputted from the SIG terminal 11. 4
f through the SO terminal 13 as a start pulse SI for the next-stage contact type image sensor ICs 15 and 16.

At this time, the flip-flop 8 receives the start pulse SI from the outside like the shift register group 4, so it is activated in the same way as the shift register group 4, and the flip-flop 8 receives the start pulse SI from the shift register 4f. , a signal of "H" level is outputted continuously, and as a result, the chip select switch 9 is kept closed only while the shift register group 4 is in operation.

The switch 10 also receives a clock pulse CL.
Since the signal level of K is closed when the signal level is "H" level and is open when it is "L" level, immediately after the image signals output from each photocell 1a to 1e are output from the SIG terminal 11, the image signal The voltage level (the potential of the signal line 7) is forcibly lowered to the GND potential. This means that unless the signal line 7 is forcibly pulled down to the GND potential each time an image signal is captured from each photocell 1a to 1e, when an image signal is captured from a photocell, the captured image signal will be the same as the previously captured image signal. This is because the potential level (a level higher than the GND potential) is added, and accurate image signals cannot be obtained thereafter.

FIG. 6 is a circuit diagram in which a plurality of ICs for contact type image sensors are connected in series, and the role of the capacitor 7 in this circuit is to
When the image signal (see FIG. 7) output from the SIG terminal 11 of C14, 15, and 16 is taken out from the SIG terminal 19, it is shaped into an integral waveform as shown in FIG.

However, the conventional contact type image sensor I
In C, when the operation of the shift register group 4 is completed, that is, when all the image signals output from each photocell 1a to 1e are output from the SIG terminal 11, the chip select switch 9 is opened. After it is in the open state, the function by switch 6 (forcibly converting the image signal to
(down to the ND potential) will no longer be achieved. Therefore, there is no means to forcibly remove the residual charge when the image signal is converted into an integral waveform, and as a result, as shown in the middle part of FIG.
Even when all the image signals have been output from the SIG terminal 11, the potential of the image signal has not yet fallen to the GND potential (effect of the residual charge in the capacitor 7), so even though all the image signals have been output, It becomes as if the output of the image signal continues, and accurate image signals cannot be obtained.

[0013] Therefore, in order to forcibly remove the residual charge in the capacitor 7, a switch 18 is provided outside the contact type image sensor IC, which is closed at the timing of "H" of the clock pulse CLK. This makes it possible to obtain accurate image signals as shown in the latter part of FIG. In addition,
Related technologies include Japanese Patent Laid-Open No. 63-76667 and Japanese Patent Laid-Open No. 1-183257.

[0014]

[Problems to be Solved by the Invention] Since the conventional contact type image sensor IC is configured as described above, it is necessary to provide a switch that can forcibly remove the residual charge of the externally provided image signal shaping capacitor. As a result, the image signal becomes inaccurate due to the influence of the residual charge. Therefore, it is necessary to connect an external switch that can forcibly remove the residual charge of the capacitor, and that switch must be connected to the board. There were issues such as securing space on top for installation and increasing costs.

The present invention has been made to solve the above-mentioned problems, and by providing an internal switch for forcibly removing the residual charge of the capacitor, the switch for removing the residual charge can be removed externally. It is an object of the present invention to provide an IC for a contact type image sensor that does not require the provision of a switch, thereby reducing costs, and also eliminates the need to secure extra space for installing a switch on a substrate.

[0016]

[Means for Solving the Problems] An IC for a contact type image sensor according to the present invention is provided with a switch that repeatedly opens and closes in response to changes in the level of a clock pulse between an image signal output terminal and a ground terminal.

[0017]

[Function] IC for contact type image sensor in this invention
By providing a switch between the image signal output terminal and the ground terminal that repeatedly opens and closes according to changes in the level of the clock pulse, the charge remaining in the image signal shaping capacitor is forcibly removed.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an IC for a contact type image sensor according to an embodiment of the present invention. In the figure, the same reference numerals as in the conventional one indicate the same or corresponding parts, and the explanation thereof will be omitted. A switch 20 is connected between the SIG terminal 11 and the GND terminal 12 and repeatedly opens and closes in response to changes in the level of the clock pulse CLK ("H" level or "L" level).

Next, the operation will be explained.

When the shift register group 4 is activated by a start pulse, each channel select switch 3a to 3e is sequentially controlled on and off to select each photocell 1a.
The point in which the image signal is outputted from the SIG terminal 11 from 1e to 1e is the same as the conventional one, so a description thereof will be omitted.

Here, FIG. 2 shows an IC for a contact type image sensor.
The role of the capacitor 7 in this circuit is to convert the image signal (see FIG. 3) output from the SIG terminal 11 of each contact image sensor IC 14, 15, 16 into a SIG. When taken out from the terminal 19, it is shaped into an integral waveform as shown in FIG.

However, as described in the explanation of the conventional example,
When the operation of the shift register group 4 is completed, that is, all the image signals output from each photocell 1a to 1e are sent to SIG.
When the chip select switch 9 is output from the terminal 11, it is in the open state, so after the chip select switch 9 is in the open state, the function of the switch 6 (forcibly lowering the image signal to the GND potential) is no longer performed, and the image signal When this is made into an integral waveform, the residual charge cannot be forcibly removed, making it impossible to obtain an accurate image signal.

Therefore, in order to forcibly remove the residual charge of the capacitor, a clock pulse CL is applied between the SIG terminal 11 and the GND terminal 12 (inside the IC for the contact type image sensor).
A switch 20 is provided that closes at the "H" timing of K. This makes it possible to obtain accurate image signals as shown in FIG.

[0024] Here, the switch 15 is connected to the other switch 9.
, 10, etc., there is almost no cost increase due to the addition of the switch 15. Also,
Since a plurality of ICs for contact image sensors are usually used in parallel, the switches 20 operate simultaneously in parallel, and the ON resistance decreases in proportion to the number of ICs in parallel, which improves the responsiveness of image output. .

Note that in the above embodiment, the photocells 1a to
Although a phototransistor is shown as 1e, a photodiode may also be used.

Further, in the above embodiment, an N-channel MOS was used as the switch 20, but a P-channel MOS may also be used.

Further, in the above embodiment, an example was shown in which the channel select switches 3a to 3e are controlled to open and close in order from the left (3a to 3e) following the operation of the shift register group 4, but the opening and closing controls may be controlled in other orders. The connection of the shift register group 4 may be changed so as to do so.

[0028]

[Effects of the Invention] As described above, according to the present invention, since a switch is provided between the image signal output terminal and the ground terminal, which repeatedly opens and closes in accordance with changes in the level of the clock pulse, the remaining power in the capacitor for image signal shaping is reduced. Since the charge is forcibly removed, there is no need to provide an external switch to remove residual charge, which results in cost reduction and frees up extra space on the board for installing the switch. This has the effect of eliminating the need to do so.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an IC for a contact type image sensor according to an embodiment of the present invention.

FIG. 2 is a circuit diagram in which a plurality of ICs for contact type image sensors shown in FIG. 1 are connected in series.

FIG. 3 is a drive timing chart of the contact type image sensor IC of FIG. 1;

FIG. 4 is a drive timing chart when a plurality of ICs for the contact type image sensor shown in FIG. 1 are connected in series.

FIG. 5 is a circuit diagram showing a conventional contact type image sensor IC.

FIG. 6 is a circuit diagram in which a plurality of ICs for contact type image sensors shown in FIG. 5 are connected in series.

FIG. 7 is a drive timing chart of the contact type image sensor IC of FIG. 5;

8 is a drive timing chart when a plurality of ICs for contact type image sensors shown in FIG. 5 are connected in series; FIG.

[Explanation of symbols]

1a to 1e Photocells 3a to 3e Channel select switch 4 Shift register group 5 Start pulse SI input terminal 6 Clock pulse CLK input terminal 7 Signal line 9 Chip select switch 11 Image signal output terminal 12 Ground terminal 20 Switch

Claims (1)

[Claims] [Claim 1] A plurality of photocells that output current when detecting light, a channel select switch connected to the current output section of each of the photocells, and a start signal that is activated by a start signal and that each of the photocells outputs. In order to sequentially output current from the image signal output terminal via a common signal line, a group of shift registers that sequentially control on/off of each of the channel select switches in accordance with the cycle of the clock pulse; A close-contact image sensor comprising a chip select switch that is closed only when the shift register group is in operation, and a switch that is connected between the image signal output terminal and the ground terminal and repeatedly opens and closes in response to changes in the level of the clock pulse. IC for use.