JPH07236041A - Picture reader - Google Patents

Abstract

PURPOSE:To provide a picture reader in which an output signal of a photoelectric conversion element is converted into a digital picture signal at a high speed. CONSTITUTION:The reader is provided with a photoelectric conversion section converting an optical signal into an electric signal, a 1st A/D converter section 102 converting an analog output signal of the photoelectric conversion section into digital data, and a D/A converter section 103 converting the digital output signal of the A/D converter section 102 into an analog signal, and also with a delay section 104 correcting a timewise deviation between the analog output signal of the photoelectric conversion section and the analog output signal of the D/A converter 103, a difference detection section 105 taking a difference between the analog output signal of the D/A converter section 103 and the analog output signal of the delay section 104, and a 2nd A/D converter section 106 converting an analog output of the difference detection section 105 into a digital signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus having a photoelectric conversion element, and more particularly to an image reading apparatus having means for converting an image signal from an output signal of the photoelectric conversion element into a digital signal at a high speed. .

[0002]

2. Description of the Related Art Conventionally, an example generally used for extracting an image signal from an output signal of a photoelectric conversion element is shown in FIG.
Shown in. Hereinafter, a conventional example will be described with reference to FIG.

The buffer amplifier 501 transmits an output signal of a photoelectric conversion element (not shown) to a circuit in the subsequent stage.

Sample / hold circuits 502, 503,
504 is a sampling pulse 50 with different timing.
7, 508, the sample / hold circuit 502 holds the reference voltage level of the output signal of the photoelectric conversion element, and the sample / hold circuit 504 holds the voltage level of the image signal. .

Further, the sample / hold circuit 503 is
In order to match the timing of the reference voltage level held by the sample / hold circuit 502 with the timing of the image signal level held by the sample / hold circuit 504, the output signal of the sample / hold circuit 502 and the timing at which the sample / hold circuit 504 holds Hold at the same timing.

Further, the differential amplifier 505 has a sampling /
The difference between the outputs of the hold circuits 503 and 504 is calculated to detect a desired image signal. A / D converter 50
Reference numeral 6 converts the output signal of the differential amplifier 505 into a digital signal at the timing of the clock 509.

[0007]

However, in the above-mentioned conventional example, when the frequency of the photoelectric conversion element becomes high, it is necessary to charge and discharge the charge of the sample / hold circuit at high speed. Must be small. However, if the capacity of the hold capacitor is made small, there arises a problem that the held voltage level easily changes.

It is an object of the present invention to provide an image reading device which converts an output signal of a photoelectric conversion element into a digital image signal at high speed.

[0009]

According to the present invention, there is provided a photoelectric conversion means for converting an optical signal into an electric signal, and a first A / A converter for converting an analog output signal of the photoelectric conversion means into digital data.
D conversion means, D / A conversion means for converting the digital output signal of the first A / D conversion means into an analog signal, and analog output signal of the photoelectric conversion means for analog output signal of the D / A conversion means A delay unit that corrects a time difference between the analog output signal of the D / A conversion unit and the analog output signal of the delay unit; and a digital output of the analog output of the difference detection unit. A second A / D conversion means for converting into a signal.

Further, according to the present invention, a photoelectric converting means for converting an optical signal into an electric signal, a first amplifying means for appropriately amplifying an analog output signal of the photoelectric converting means, and an analog of the first amplifying means. First A / D conversion means for converting an output into a digital signal, the first amplification means, and the first A / D conversion means.
First voltage limiting means, which is arranged between the A / D converting means and prevents the analog output of the first amplifying means from exceeding the input voltage range of the first A / D converting means; Second amplification means for amplifying the analog output signal of the means by N times the amplification factor of the first amplification means by 2 (N is a natural number), and the analog output signal of the second amplification means to a digital signal The second A / D conversion means for conversion is disposed between the second amplification means and the second A / D conversion means, and the analog output of the second amplification means is the second A / D conversion means.
Second so as not to exceed the input voltage range of the D / D conversion means
Of the first A / D conversion means and a digital calculation means for calculating the digital output signal of the second A / D conversion means.

[0011]

EXAMPLE FIG. 7 is a sectional view showing the external appearance of the apparatus according to the first example of the present invention.

In FIG. 7, the image scanner unit 201
Is a part that reads a document and performs digital signal processing. Further, the printer unit 200 includes the image scanner 20.
1 is a portion for printing out an image corresponding to the original image read in No. 1 on paper in full color.

Next, in the image scanner section 201, the original pressure plate 202 is used to scan the original 204 on the original platen glass (hereinafter referred to as a platen) 203 with the halogen lamp 20.
It is illuminated with the light of 5. The light reflected from the document is reflected by the mirror 20.
The image is formed on a 3-line sensor (hereinafter, referred to as CCD) 210 by a lens 208 by being guided to the image pickup device 6 and 207. The lens 208 is provided with an infrared cut filter 231.

The CCD 210 color-separates the light information from the original document, reads full-color information components of red (R), green (G), and blue (B), and sends them to the signal processing unit 209. Each color component reading sensor array of the CCD 210 is composed of 5000 pixels. As a result, an A3 size document, which is the largest size of the documents placed on the platen glass 203, is 297 mm in the lateral direction.
Is read at a resolution of 400 dpi.

The halogen lamp 205 and the mirror 20
6 is a velocity v, and the mirror 207 is mechanically movable at a (1/2) v in a direction (hereinafter, referred to as a sub-scanning direction) perpendicular to an electric scanning direction (hereinafter, referred to as a main scanning direction) of the line sensor. Thus, the entire surface of the original is scanned.

The standard white plate 211 includes sensors 210-1 to 210-1.
The correction data of the read data of the R, G, and B sensors 210-3 is generated.

The standard white plate 211 has a substantially uniform reflection characteristic with visible light and has a white color in the visible.
Using this standard white plate 211, the sensors 210-1 to 21-21
The output data of the visible sensors 0 to 3 are corrected.

The signal processing unit 209 electrically processes the read signal, decomposes it into magenta (M), cyan (C), yellow (Y), and black (BK) components, and sends them to the printer unit 202. . In addition, the image scanner unit 201
For each document scan (scan) in M, C,
One component of Y and BK is sent to the printer 200,
A total of four document scans completes one printout.

The image signals of M, C, Y and BK sent from the image scanner unit 201 are laser driver 21.
Sent to 2. The laser driver 212 modulates and drives the semiconductor laser 213 according to the image signal. Laser light
Polygon mirror 214, f-θ lens 215, mirror 2
The photosensitive drum 217 is scanned via the image pickup device 16.

The developing devices 219 to 222 are magenta developing device 219, cyan developing device 220, yellow developing device 221, and
The black developing device 222 includes four developing devices alternately contacting the photosensitive drum, and develops the electrostatic latent images of M, C, Y, and BK formed on the photosensitive drum 217 with the corresponding toners.

The transfer drum 223 is a paper cassette 224.
Alternatively, the paper fed from 225 is transferred to the transfer drum 22.
3 and the toner image developed on the photosensitive drum 217 is transferred onto a sheet.

In this way, after the four colors of M, C, Y, and BK have been sequentially transferred, the paper passes through the fixing unit 226 and is discharged.

The above is the outline of the operation of the entire apparatus.

Next, the image scanner 201 will be described in detail.

FIG. 8A shows the CCD 2 in this embodiment.
It is a perspective view which shows the structure of 10.

Here, 210-1 is a light receiving element array for reading red light (R), and 210-2 and 21
Similarly, 0-3 are light receiving element arrays for reading the G wavelength component and the B wavelength component. 210-1 to 210-
Each of the R, G, and B sensors up to 3 has an opening of 19 μm in the main scanning direction and the sub-scanning direction.

These three light receiving element arrays having different optical characteristics are monolithically arranged on the same silicon chip so that the R, G and B sensors are arranged in parallel with each other to read the same line of the original. It is configured.

By using the CCD having such a structure,
An optical system such as a lens is common for each color separation reading. This makes it possible to simplify the optical adjustment for each color of R, G, and B.

FIG. 8C is a sectional view taken along the dotted line in FIG. 8A.
Shown in.

A photosensor 210-1 for reading R and photosensors 210-2 and 210-3 for reading visible information of G and B are arranged on a silicon substrate 210-5.

On the R photo sensor 210-1, an R filter 210- that transmits a red wavelength component of visible light is transmitted.
7 is placed. Similarly, a G filter 210-8 is arranged on the G photo sensor 210-2, and a B filter 210-9 is arranged on the B photo sensor 210-3. Further, 210-6 is a flattening layer made of a transparent organic film.

FIG. 8B is an enlarged view showing the structure of the light receiving element. Each sensor has a length of 10 μm per pixel in the main scanning direction. Each sensor has 5000 pixels in the main scanning direction so that the short-side direction (297 mm) of the A3 document can be read at a resolution of 400 dpi. The line distance between the R, G, and B sensors is 80 μm, and each line is separated by 8 lines for a sub-scanning resolution of 400 dpi.

FIG. 1 is a circuit diagram showing an outline of a control circuit in this embodiment, and FIG. 2 is a timing chart showing each signal in this embodiment.

The buffer amplifier 101 is a CC (not shown).
The analog image signal 107, which is the D output signal, is transmitted to the circuit in the subsequent stage.

The first A / D converter 102 uses the clock 1
According to the timing of 107, the analog image signal 10
The reference voltage of the image signal in 7 is converted into a digital image signal 109 which is a digital signal. The first A / D
The digital image signal 109 which is the output of the converter 102.
Is input to the subsequent D / A converter 103 and is converted into the analog image signal 110 again.

The delay line 104 is the D / A converter 103.
Of the analog signal 110 which is an output signal of the buffer amplifier and the image signal portion of the analog signal 108 which is an output of the buffer amplifier.

The differential amplifier 105 is the D / A converter 1
The analog signal 110, which is the output signal of 03, and the analog signal 109, which is the output signal of the delay line 104, are input. The differential amplifier 105 obtains a difference between the analog signal 109 and the analog signal 110 and detects an analog image signal 111 including only an image component. Image signal 1 which is the output signal of the differential amplifier 105
11 is input to the subsequent second A / D converter 106,
Digital image signal 11 at the timing of clock 1108
Converted to 2.

Through the above process, the analog image signal of the photoelectric conversion element is converted into a digital image signal by detecting only the image signal component.

The output voltage range of the differential amplifier 105 is smaller than the input voltage range of the second A / D converter 106, and the saturation recovery characteristic is excellent.

FIG. 3 is a circuit diagram showing an outline of the control circuit in the second embodiment of the present invention, and FIG. 4 is a timing chart showing each signal of the present embodiment.

First, the analog image signal 308 is an output signal of a photoelectric conversion element such as a CCD (not shown), and the buffer amplifier 301 is for transmitting the analog image signal 308 to a subsequent circuit. Three
09 is output.

The amplifier 304 uses the analog image signal 3
09 is input, and it is amplified appropriately and analog image signal 3
12 is output. The first A / D converter 306 inputs the analog signal 312 and converts the image signal portion of the analog signal 312 into a digital image signal 314 at the timing of a clock 317.

The amplifier 302 uses the analog image signal 3
09 is input, and the analog image signal 310 amplified to N-fold of the amplification factor of the amplifier 304 is output. Second
The A / D converter 305 receives the analog image signal 311 which is the output signal of the limiter 303.

The limiter 303 outputs the analog image signal 311 whose voltage range is limited so that the analog image signal 310 does not exceed the input range of the second A / D converter 305. The second A / D converter 3
Reference numeral 05 converts the portion of the analog image signal 311 which is the image signal reference into the digital signal 313 at the timing of the clock 316.

The digital calculator 307 subtracts the digital signal 313 from the digital signal 314 and outputs a digital image signal 315 in which only the image portion is extracted.

When the amplification factor of the amplifier 304 is A, the amplification factor of the amplifier 302 is A × 2 ^N (N is a natural number). Therefore, assuming that the resolution of the first A / D converter 306 is X bits and the resolution of the second A / D converter is Y bits, the digital image signal 315 becomes X bits.
It is a digital signal corresponding to + N (where N ≦ Y) bits.

In the above second embodiment, two A /
The apparent resolution of the A / D converter was increased by changing the amplification factor of the analog signal input to the D converter, but the amplification factor of the input signal was made equal, and the magnitude of the reference voltage of the A / D converter was increased. The same effect can be obtained by changing.

FIG. 9 is a circuit diagram showing the outline of the control circuit in the third embodiment of the present invention.

The buffer amplifier 901 transmits the analog image signal 906 which is the output of the photoelectric conversion element (not shown) to the subsequent circuit as the analog image signal 907. The first A / D converter 902 converts the image signal portion of the analog image signal 907 into a digital image signal 909 at the timing of the clock 912.

The second A / D converter 903 converts the voltage value of the reference image signal portion of the analog image signal 908 into a digital image signal 910 at the timing of the clock 913. Reference voltage 9 of the second A / D converter 903
15 is a reference voltage 91 of the first A / D converter 902.
It is 1/2 ^{N of} 4 (N is a natural number).

The limiter 904 outputs the analog image signal 908 so that the voltage level of the analog image signal 907 does not exceed the set voltage level of the reference voltage 915 of the second A / D converter 903. The digital image signal 909 and the digital image signal 910 are converted by a digital calculator 905 into a digital image signal 911 in which only the image signal is extracted.

[0052]

As described above, according to the present invention,
By using the A / D converter instead of the sample / hold circuit, there is an effect that the output signal of the photoelectric conversion element can be converted into a digital image signal at high speed.

[Brief description of drawings]

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

FIG. 2 is a timing chart showing the operation of the first embodiment.

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

FIG. 4 is a timing chart showing the operation of the second embodiment.

FIG. 5 is a circuit diagram showing a conventional configuration example.

FIG. 6 is a timing chart showing a conventional operation.

FIG. 7 is a cross-sectional view showing a structure in each example of the present invention.

FIG. 8 is an explanatory diagram illustrating an image scanner according to each embodiment of the present invention.

FIG. 9 is a circuit diagram showing a third embodiment of the present invention.

[Explanation of symbols]

 101 ... Buffer amplifier, 102 ... First A / D converter, 103 ... D / A converter, 104 ... Delay line, 105 ... Differential amplifier, 106 ... Second A / D converter, 107, 108, 110, 111 ... Analog image signals, 109, 112 ... Digital image signals.

Claims (2)

[Claims] 1. A photoelectric conversion means for converting an optical signal into an electric signal; a first A / D conversion means for converting an analog output signal of the photoelectric conversion means into digital data; and the first A / D conversion. D / A conversion means for converting the digital output signal of the means into an analog signal; delay means for correcting the time lag between the analog output signal of the photoelectric conversion means and the analog output signal of the D / A conversion means; A difference detecting means for obtaining a difference between the analog output signal of the D / A converting means and the analog output signal of the delay means; and a second A / D converting means for converting the analog output of the difference detecting means into a digital signal. An image reading apparatus comprising: 2. A photoelectric conversion means for converting an optical signal into an electrical signal; a first amplification means for appropriately amplifying an analog output signal of the photoelectric conversion means; and an analog output of the first amplification means as a digital signal. A first A / D converting means for converting into a first A / D converting means; and an analog output of the first amplifying means arranged between the first amplifying means and the first A / D converting means. First voltage limiting means for preventing the input voltage range of the D / D conversion means from being exceeded; an analog output signal of the photoelectric conversion means being N of 2 which is an amplification factor of the first amplification means.
(N is a natural number) Second amplification means for amplifying by multiplication; second A / D conversion means for converting an analog output signal of the second amplification means into a digital signal; and second amplification means A second voltage limit which is arranged between the second A / D conversion means and prevents the analog output of the second amplification means from exceeding the input voltage range of the second A / D conversion means. An image reading apparatus comprising: a digital calculating unit for calculating a digital output signal of the first A / D converting unit and a digital output signal of the second A / D converting unit.