JPS62183171A - Photosenser driving integrated circuit - Google Patents

Abstract

PURPOSE:To selectively pick up a signal charge out of an output line of only one photosensor driving integrated circuit for reducing total output capacity making reading with high sensitivity and at high speed feasible by a method wherein said circuit is composed of a scanning pulse generating circuit and switch elements to be provided with output change-over switch elements. CONSTITUTION:Signal charges are successively actuated from a photosensor driving integrated circuit 41 connected to output the signal charges in time series corresponding to the arrayal order of a-Si photoelectric conversion elements 11. For example, when a signal charge is read out of No.n photosenser driving integrated circuit 41, the output change-over switch element 13 only in the integrated circuit 41 is turned on while the other output change-over switch 13 in other integrated circuit is turned off. At this time, the drain diffused capacity and the interconnection capacity on photosensor driving integrated circuit are concentrated on the capacity of output change-over switch element 13 turned on. the drain diffused capacity of output change-over switch element 13 itself turned off is included of course but it is almost negligible due to far less number than that of switch element 5. Resultantly, the time constant is reduced making high speed reading feasible while improving the noise resistance.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an integrated circuit for driving an optical sensor, and in particular to a contact type image sensor used as a photoelectric conversion device in facsimiles, optical character recognition, image scanners, copying machines, etc. For driving optical sensor! Regarding A product circuits.

[Conventional technology]

Compared to MO3 type IC image sensors, CCD image sensors, and the like, the contact type image sensor does not use a reduction optical system using a lens, so it can realize a facsimile machine and the like in a smaller size and is more economical. The photoelectric conversion material for this contact image sensor is amorphous silicon (hereinafter referred to as a-
(written as Si) is often used these days. This a-Si
has a high specific resistance (CCD image sensor, MO3 type i, etc.)
Similar to image sensors, it is suitable for charge accumulation mode operation. In this case, a structure in which a-Si is sandwiched between upper and lower electrodes is usually used as the element structure, but by adopting such a sandwich structure, it is possible to achieve a high optical response speed of the element of Il, ]rns. An image sensor suitable for high-speed reading devices can be obtained.

In order to make full use of the high light sensitivity and high speed of the double a-Si photoelectric conversion element, and to achieve a compact contact type image sensor, a dedicated photosensor driving integrated circuit was installed in the photoelectric conversion FfA. Mounting on the same board with the element array is impossible, and by mounting on the same board, the wiring is shorter than in the case of a discrete drive circuit that is not mounted on the same board, reducing cross noise, etc. Reduce.

A equipped with multiple integrated circuits for driving optical sensors like this
As a Si contact type image sensor, there is a contact type image sensor shown in ``RA-Si Heterocontact Photo 1 - Afterimage Characteristics of Diodes'' (Lecture No. 2-3), Proceedings of the 1985 National Conference of the Television Society of Japan. Conventionally, such an integrated circuit for driving an optical sensor has an input/output terminal bar...I provided on a semiconductor substrate 1, as shown in a perspective view in FIG.
A scanning pulse generating circuit 3, which is controlled by clock pulses and the like inputted from the computer 2, and is composed of, for example, a multi-stage static shift register, sequentially generates scanning pulses. Although not shown in the figure, there are a plurality of pads 4 for human power and terminals on the semiconductor substrate 1F, for example, on an insulating substrate such as a glass [7;
The a-S i is connected one-to-one to, for example, a bonding wire, with the photoelectric conversion element of the aS1 optical conversion grid array provided together with the integrated circuit for driving the optical sensor of l.
The signal charges generated in the 'IQ' 1E conversion element array are controlled by each bin output of the state shift register described above, and one terminal is connected to the output terminal 4 for the input terminal.
The other terminal of each switch element 5 is connected to the commonly connected output line through the switch element 5 which is connected in a pair to the output terminal pad 6/\\ of one optical sensor. The number of stages per driving integrated circuit is usually 64 or 128, depending on the circuit scale, the number of pads, the yield rate, and the alignment of the glass substrate to be mounted, etc.
steps etc. are used.

For example, a 3456-element a-S' + photoelectric conversion element array formed on an A4 size, 16-element glass substrate is scanned and driven by a 128-stage photosensor driving integrated circuit. In this case, 27 optical sensor driving integrated circuits are installed. A schematic diagram of the contact type image sensor constructed in this manner is shown in FIG. The operation of each optical sensor driving integrated circuit 41 is as described with reference to FIG. 3, and for example, the 27 optical sensor driving integrated circuits 41 repeat the same operation starting from the first one. The output terminal pad 6 of each photosensor driving integrated circuit 41 is formed on a glass substrate l, for example.
.

They are commonly connected at the top and connected to a signal output terminal 7 as a contact type image sensor. This is for reliability of connection with the outside and simplification of external signal processing circuits, etc. All signal outputs from the a-8i photoelectric conversion element array are read out as time-series signals from the signal output terminal 7 serving as the contact type image sensor. At this time, the signal output voltage 5 and response speed (time constant τ) for each element are determined by cL, respectively, using the values of the total output capacitance 8 and load resistance 9 shown in FIG.

The total output capacity 8 is made up of the output capacity of the 27 optical sensor driving integrated circuits 41, and specifically, the total output capacity 8 is
It consists of the drain diffusion capacitance of each switch element 5 consisting of FET, the sum of l, the optical sensor driving integrated circuit 41, and the output line wiring capacitance on the glass substrate 10, for example. The drain diffusion capacitance of the switch element 5 can be reduced by reducing the dimensions of the transistor, but is limited by process limitations and performance factors such as the length ratio, width, and length ratio.

The wiring capacitance is limited by the wiring resistance. For the above reasons, the total output capacity 8 is usually at least 4 ('
) 0~・500PF roar. For example, load resistance 9t
If it is 1 kΩ, the time constant will be about 400 to 500 ns.
To sell 8 in s,/line, 250 per element.
ns, considering the resetting period in the external circuit, it is necessary to read within half 12"ins, so the load resistance 9 must be at least the above 1, /' 10, that is, 100 Ω or less. 7 Large Due to the total output capacitance 8, the small signal output voltage is not proportional, but it decreases further as the load resistance increases, and since the signal charge itself is small due to high-speed reading, it becomes so small that it cannot be separated from fixed pattern noise etc. One possible solution to this problem is to connect the output terminal pads 6 of each optical sensor driving integrated circuit 41 to an external signal processing circuit as multiple output terminals without connecting them in common. In this case, the number of output terminals increases, resulting in poor connection reliability and the need for as many external signal processing circuits as output terminals, resulting in problems such as circuit complexity, cost, and increased E.

[Problems to be Solved by the Invention] The above-described conventional optical sensor driving integrated circuit has a drawback in that it cannot fully utilize the high contrast ratio and high speed of the photoelectric conversion element because of its large output capacity.

An object of the present invention is to provide a contact image sensor with high sensitivity without reducing the reliability of connection with an external signal processing circuit or complicating the external signal processing circuit.

An object of the present invention is to provide an optical sensor driving integrated circuit capable of high-speed reading operation.

[Means for solving problems]

The optical sensor driving integrated circuit of the present invention includes a scanning pulse generation circuit formed by cascading a plurality of unit circuits, a group of switch elements each controlled by an output of one output per unit time, and each switch. An input terminal bar group connected to one terminal of each switch element, and an output terminal bar group connected to an output line that commonly connects the other terminal of each switch element. - An integrated circuit for driving a photosensor comprising at least a node, which has an output changeover switch element inserted between the output line and the output terminal bar.

1 Effect '1 In the present invention, since the present invention is provided with an output changeover switch element that opens and closes the output line of the integrated circuit for driving an optical sensor, which is composed of a scanning 1< pulse generation circuit and a switching element, the integrated circuit for driving an optical sensor is Even if multiple units are installed and their output terminal pads are connected in common, the output I opens and closes each output line.
With the JJFIA switch element, a signal can be selectively extracted from only the output line of one photosensor driving integrated circuit, and the total output capacity can be significantly reduced. Since the signal output voltage and reading speed are inversely proportional to this output capacity, high sensitivity and high speed reading are possible.

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

FIG. 1 is a perspective view of the main parts of a contact type image sensor for explaining one embodiment of the present invention, and the equivalent circuit of circuit elements and wiring is shown by dashed lines.

This embodiment consists of a scanning pulse generation circuit 3 consisting of a state shift register formed by vertically connecting a plurality of unit circuits each consisting of a flip-flop and a flip-flop.
A group of switch elements 5 consisting of MOS FETs controlled by the output of the knob, a group of input group parameter pads 4 connected to one terminal of each switch element 5, and each switch element 5. In the optical driving integrated circuit 41, the optical driving integrated circuit 41 includes at least an output terminal pad 6 connected to an output line 17 that commonly connects the other terminal of the output line 17.
MOSFET inserted between and the output terminal pad 6
It has an output changeover switch element 13 consisting of. 14 is a bonding pad connected to the gate of a MOS FET which is an output changeover switch.

Next, a contact type image sensor using this optical sensor driving integrated circuit will be explained. Each input terminal pad 4 on the semiconductor substrate 1 is provided on an insulating substrate 10 made of glass or the like together with a plurality of optical sensor driving integrated circuits.
-Si photoelectric conversion elements 11 are connected one-to-one by bonding wires 15, for example. a-Si photoelectric conversion element 1
The signal charges generated in 1 are sequentially controlled by scanning pulses on the semiconductor substrate 1, and one of the terminals is connected to the input terminal pad 4.
The other terminals of the switch elements are outputted to the commonly connected output line 17 through switch elements 5 made of, for example, MOS FETs connected in a one-to-one manner.

Signal charges from a plurality of integrated circuits for driving photosensors are passed through output terminal pads 6 and connected to an output terminal pad 6, for example, on an insulating substrate 10, which is connected with a bonding wire 16. It is commonly output to all output lines 12 of the book.

Next, the operation of this contact type image sensor will be explained.

For example, the optical sensor driving integrated circuits 41 connected in the order of arrangement are sequentially operated so as to output signal charges in time series according to the arrangement order of the a-Si photoelectric conversion elements 11. For example, when a signal charge is being read out from the first photosensor driving integrated circuit 41, the output switching switch element 13 in that integrated circuit is on, and the output switching switch element 13 in the other integrated circuit is on. The output changeover switch element 13 is off. When signal charges are being read from the second photosensor driving integrated circuit 41, only the output changeover switch element 13 in that integrated circuit is similarly turned on.

Repeat the same process below.

FIG. 2 is an equivalent circuit diagram during operation of a contact type image sensor using this embodiment.

By providing the output changeover switch element 13, the on-resistance 21 Ro of the output changeover switch element 13 is equivalently reduced.
This differs from the conventional one in that n□ is added and the capacitance CL of the total output capacitance 22 is reduced. Here, the operating speed is determined by the rise and fall speeds of the signal output waveform.The rise time constant is determined by setting the capacitance of the element capacitor 23 to <2゛[+, and setting the on-resistance 24 of the switch element 5 to 1 (( As mouth 1 (:, 1.
+ ・(+1(1111+fion2), the falling time constant is set as (EL-R) with the load resistance 25 as R1.In reality, C[+ is set as 2PF, (Roll
+Ron2) is 21 (Ω), the rise time constant is about 4 ns at most, and from this point there is no problem with the reading speed.As mentioned earlier, the total output capacitance is
The drain diffusion capacitance of the Soji element 5 and the wiring capacitance on the optical sensor driving integrated circuit and the glass substrate 10, or in the case of this embodiment, the drain diffusion capacitance and the wiring capacitance on the optical sensor driving integrated circuit are the output. The switching switch...I switch element 13 is the only one that is on, and of course it includes the drain diffusion capacitance of the output switching switching element 13 itself that is off, but compared to the number of switching elements 5. Much less licking and almost no problem. Therefore, for example,
In the case of A4 size, 16 elements, /”min, 1
When 28 stages of optical sensor driving integrated circuits are not mounted on the F, the load capacitance CL is several tens of pF, which is about 1/10 or less. Even if the resistance R1 of the load resistor 25 is set to 1Ω, the falling time constant is reduced to about 50 ns, making it possible to read at a high speed of 1 rn 3 , y line or less. In addition, the signal output voltage Vs is more than 10 times that of the conventional one, and has high noise resistance.
Signal processing is also facilitated by switching element 5 and output switching element 13.
is a single channel MO8FE such as N channel or P channel
Of course, it does not matter if it is not only T but also CMO3. In this embodiment, the integrated circuit for driving the photosensor is configured with only one output changeover switch element 13, but for example, among the 128 stages, the output lines of the front half B4 stages and the output lines of the rear half 64 stages and two It is also possible to have a structure in which the output changeover switch element 3 is provided separately for each book.

〔Effect of the invention〕

As explained below, according to the present invention, by providing an output changeover switch element in an integrated circuit for driving an optical sensor, the total output capacity of a contact type image sensor in which a plurality of integrated circuits for driving an optical sensor are mounted can be increased. It has the advantage of being extremely small and achieving high-speed reading operations. At the same time, since a large signal output voltage can be obtained, noise resistance is high, and signal processing is also facilitated. In particular, it is also effective in detecting weak signal charges at high speed and high resolution. Moreover, since only the output changeover switch element is provided, there is no increase in man-hours, the reliability of connection with external signal processing circuits, etc. is high, and the connection is high-yield without complicating external signal processing circuits, etc. This has the effect of realizing a shaped image sensor.

[Brief explanation of drawings]

FIG. 1 shows a close-contact type I for explaining one embodiment of the present invention.
FIG. 2 is an equivalent circuit diagram of the contact type image sensor shown in FIG. 1 during operation. FIG. 3 is a perspective view of a conventional optical sensor driving integrated circuit. FIG. 3 is a schematic diagram of a contact type image sensor. DESCRIPTION OF SYMBOLS 1... Semiconductor substrate, 2... I/O terminal bar, 3... Scanning pulse generation circuit, 4... Input terminal bar/rad, 5... Switch resistor, 6 ...Para-rad for output terminal, 7...Signal output terminal, 8...Total output capacity,
9...Load resistance, 1()...Glass substrate, 11...
・a-8i photoelectric conversion element, 12...all output lines, 13・
... Output changeover switch element, 14... Bonding pass, 15.16... Bonding wire, 17
... Output line, 22... Total output capacity, 23... Element capacitance, 24... On-resistance of switch element, 25...
Load resistance, 41... integrated circuit for driving the optical sensor. Half zTfZJ 22: , Zenkoku hgdou (C muno 23: Shu"rt* (cv) 2φ2 Suinote Soshi Rikiman'-4a (F?an l
) 2S: White gourd ↑ Direct gt) Vr: Iasumi at t] Gan Vs: 4 fortune 3 out or voltage

Claims (1)

[Claims] A scanning pulse generation circuit formed by connecting a plurality of unit circuits in cascade, a group of switch elements each controlled by the output of each of the unit circuits, and a group of pads for input terminals each connected to one terminal of each of the switch elements. and an output terminal pad connected to an output line that commonly connects the other terminal of each of the switch elements, wherein the integrated circuit for driving an optical sensor includes: An integrated circuit for driving an optical sensor, comprising an output changeover switch element inserted in the integrated circuit.