JPS60163565A - Original reader - Google Patents

Abstract

PURPOSE:To attain original reading with small size and high S/N by converting a video signal line included in a drive circuit of a photodetector into a low impedance and extracting it via a flexible cable or the like after a signal electric charge amount is amplified. CONSTITUTION:Drive IC 5, 6 to drive a thin film photodetector 2 are mounted on a substrate 1 made of glass on which the element 2 is formed. The IC 5, 6 has a function driving the element 2 and also a function of low impedance conversion of signal line and signal amplification, and the IC 5, 6 are connected to a signal processing circuit 3' for binary-coding a video signal via flexible cables 7, 7'. A power supply for the IC 5, 6, a control signal of TTL level and a video signal amplified and subject to low impedance convertion are transmitted through the cables 7, 7'. Thus, the signal is not affected with propagation noise of external disturbance and the S/N is improved.

Description

[Detailed description of the invention] [Field of application of the invention] The present F! A relates to a document reading device such as a facsimile transmitting device or a copying device using a same-magnification receiving element, and particularly relates to a document reading device having a structure suitable for improving the signal-to-noise ratio.

[Background of the invention]

In a conventional same-size original reading device, the light receiving element and the driving circuit are formed on separate substrates, and have a structure in which they are all connected by a wire such as a flexible cable. However, the amount of signal charge from the photodetector array is only a few pc, and the impedance of the photodetector is extremely high.These high impedance parts are exposed, making them susceptible to propagation noise, so it is necessary to apply sufficient shielding. However, in particular, it is affected by the noise generated from the switching power supply used for the purpose of miniaturizing the device, and this has disadvantages such as extremely lowering the S/N ratio and making it impossible to realize a compact and low-cost document reading device. there were.

FIG. 1 (αL(A) is a structural plan view and a cross-sectional view, respectively, showing an example of this type of conventional document reading device.
In α) and (A), a light receiving element 2 formed on a substrate (light receiving element substrate) 1 made of glass or the like includes a structure connected to a drive shaft and a signal processing circuit 5 via a flexible cable asa't''.

A video signal line passes through the flexible cables 4 and 4', and the impedance of this signal line is generally several 1.
The amount of signal charge passing through the signal line is extremely small, about several pc.

Therefore, the flexible cable is easily affected by switching noise generated from the power supply unit in the document reading device, noise generated from the high-speed logic section in the device, and disturbance noise generated from the outside, that is, propagation noise.
As a result, the signal-to-noise ratio of the signal deteriorated.

FIG. 2 is a specific circuit diagram of the document reading device shown in FIGS. 1(a) and 1(A), and for simplicity, the circuit is configured in a 6×3 matrix. In FIG. 2, the light receiving element substrate 1
Above, a pair of thin film blocking diodes 8 and a thin film photodiode (light receiving element) 9 are connected in series so that the polarities are opposite to each other to form one element, and only a plurality of such individual elements are arranged in a straight line. They are arranged to form equal size receiving elements 2 and connected as shown. In this way, the analog switches 10 are sequentially switched by the shift register 13 of the drive and signal processing circuit 3, and the target voltage V of the target voltage source 11 is applied to the blocking diode 8 side of the light receiving element 2 via the flexible cable 4. When flexible cable 4'
The photodiode 9 side of the photodiode 2 connected to the photodiode 9 side is changed from the blocking voltage VB side of the blocking voltage source 12 to the low input impedance amplifier 14 side by sequentially switching the analog switches 10' by the shift register 13'. The signal charge of the light receiving element 2 is read. The read signal is subjected to signal processing such as binarization by a binarization circuit 17 via an integrator 15 and a sample-and-hold circuit 16, and then extracted. Since the light-receiving element 2 is composed of the photodiode 9 and the like, the video signal line included in the flexible cables 4 and 4/ constitutes a high-impedance portion, and is therefore susceptible to propagation noise, which can degrade the S/N ratio. Recognize.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a small, low-cost document reading device that has a high signal-to-noise ratio and is free from the effects of propagation noise.

[Summary of the invention]

The present invention focuses on the fact that the drawbacks of the prior art described above can be eliminated by converting the video signal line included in the drive circuit of the light receiving element to low impedance, amplifying the signal charge amount, and then taking it out via a flexible cable etc. By mounting the drive circuit, including the impedance conversion function, on the same substrate as the light receiving element, the shadow of propagation noise*1 can be eliminated.
This is a document reading device designed to improve the N ratio.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 6(α) and 6(b) are a structural plan view and a sectional view, respectively, showing an embodiment of the document reading device according to the present invention. Third
In FIGS. (α) and (A), driving ICs 5 and 6 for driving the light receiving element 2 are mounted on a substrate (light receiving element substrate) 1 made of glass or the like on which the thin film light receiving element 2 is formed. In addition to the function of driving the light-receiving element 2, the drive IC 5.6 also has the function of amplifying the signal and converting the signal line to low impedance. Furthermore, it has a structure in which the drive ICs 5 and 6 are connected to a signal processing circuit 3' for performing binarization of the video signal through a flexible cable 7.7''i. , 6 power supply and TTL level control signal and increase @b
and low-impedance converted video signals.

Therefore, the signal-to-noise ratio is improved without being affected by disturbance propagation noise as shown in Fig. 1←) and (h).

FIG. 4 is a specific circuit diagram of the document reading device shown in FIGS. 3(α) and (A), and, like FIG. 2, the circuit has a 3×3 matrix configuration for simplicity.

In FIG. 4, a pair of thin film blocking diodes 8 and a thin film photodiode 9 are connected in series on a light receiving element substrate 1 so as to have opposite polarities to form one element, and a plurality of such individual elements are connected in series. The same size receiving element 2 is formed by arranging the same number of pieces in a straight line. Also, drive I
A shift register 13, an analog switch 10, and a target voltage V source 11 are formed in C6, and are mounted on the light receiving element substrate 1. In one drive IC 5, there are a shift register 13, an analog switch 10', a blocking voltage VE source 12, an amplifier 14, and an integrator 15.
A sample and hold circuit 16 and the like are formed, and are also mounted on the light receiving element substrate 1. Furthermore, the driving ICs 5 and 6 on the same light receiving element substrate 1 are connected to a signal processing circuit 3' including a binarization circuit 7 and the like via a flexible cable 7.7'. Furthermore, this flexible cape
The power supply for the drive ICs 5 and 6, control signals, and amplified and low impedance converted signals pass through L/7.7'.

With this configuration, the shift register 13 of the drive IC 6 sequentially switches the analog switches 10 to apply the target voltage VT of the target voltage source 11 to the blocking diode 8 side of the light receiving element 2. The photodiode 9 side is switched from the blocking voltage FB side of the blocking voltage source 12 to the low input impedance amplifier 14 side by sequentially switching the analog switches 10' by the shift register 13', thereby reading the signal charge of the light receiving element 2. It will be done. Note that the read signal is amplified by an amplifier 14 and then sent to an integrator 15.
The flexible cable 6 is shaped into a waveform by
The signal is connected to the binarization circuit 7 of the signal processing circuit 3' through the signal processing circuit 3', where it undergoes signal processing such as binarization and is extracted.

In this way, in this embodiment, the signal from the light receiving element is amplified and converted to low impedance before being extracted to the outside via a flexible cable, etc.
There is no influence from switching noise generated from the power supply unit in the document reading device, noise generated from the high-speed logic section within the device, disturbance noise generated from the outside, or propagation noise, and as a result, the signal SN is reduced.
By improving the ratio, a highly accurate document reading function is realized.

Note that the light receiving element in the above embodiments is not limited to a photodiode array, but may be another photoelectric conversion element such as a photoconductive element. Furthermore, the I/J configuration of the drive circuit is not limited to the above.

〔Effect of the invention〕

As explained above, according to the present invention, by adopting an appropriate structure in which the light-receiving element and the driving circuit are formed on the same substrate without particularly changing the circuit configuration, the p and SN ratios are improved and the size is small. A low-cost document reading device is provided.

[Brief explanation of drawings]

Figures 1 (α) and (b) are a plan view and a sectional view illustrating a conventional document reading device, Figure 2 is a circuit diagram, and Figure 3 (α
) and (A) are a plan view and a sectional view showing an embodiment of the document reading device according to the present invention, and FIG. 4 is a circuit diagram. 1... Board 2... Light receiving element 3'... Signal processing circuit 5, 6... Drive IC 7, 7
'... Flexible cable 8... Blocking diode 9... Photodiode 10, 10'... Analog switch 15, 15'... Shift register 14... Amplifier 15... Integrator, 2 1 side (b figure < b5

Claims (1)

[Scope of Claims] 1. A light-receiving element formed by arranging a plurality of elements in which a pair of photoelectric conversion elements and a blocking diode are all connected in series on the same substrate, and the photoelectric conversion of the light-receiving element mounted on the same substrate. A document reading device that includes a drive circuit that sequentially reads signal charges of elements and a signal processing circuit that processes the read signals. 2. The document reading device according to claim 1, wherein the photoelectric conversion element is a thin film photodiode. 3. The document reading device according to claim 1, wherein the photoelectric conversion element is a photoconductive element. 4. The document reading device according to claim 1, wherein the drive circuit includes amplifying means for amplifying the read signal. 5. The document reading device according to claim 1, wherein the drive circuit includes means for converting the signal line impedance of the read signal to a low impedance.