JPH0419073U

JPH0419073U -

Info

Publication number: JPH0419073U
Application number: JP5840990U
Authority: JP
Priority date: 1990-06-04
Filing date: 1990-06-04
Publication date: 1992-02-18

Description

[Brief explanation of the drawing]

第１図乃至第５図は本考案の一実施例を示すも
ので、第１図はブロツク図、第２図は画像信号の
構成を示す図、第３図は可変利得増幅器及び利得
制御回路の具体回路図、第４図は自動利得制御増
幅器の利得制御特性を示すグラフ、第５図は画像
信号の可変利得制御によるレベル変化を説明する
ための波形図、第６図及び第７図は本考案の他の
実施例を示すブロツク図、第８図は従来例を示す
ブロツク図である。１１……ラインセンサ、１２……可変利得増幅
器、１３……アナログ／デジタル変換器、１５…
…ピークホールド回路、１６……Ａ／Ｄ変換器基
準電圧作成回路、１７……誤差増幅器、１８……
利得制御回路、２１……マイクロプロセツサ、２
３……メモリ、２４……原稿ＩＤ情報入力部、３
４……光量調整回路。 Figures 1 to 5 show an embodiment of the present invention. Figure 1 is a block diagram, Figure 2 is a diagram showing the configuration of an image signal, and Figure 3 is a diagram of a variable gain amplifier and gain control circuit. A concrete circuit diagram, Fig. 4 is a graph showing the gain control characteristics of the automatic gain control amplifier, Fig. 5 is a waveform diagram for explaining level changes due to variable gain control of the image signal, Figs. 6 and 7 are from this book. A block diagram showing another embodiment of the invention, and FIG. 8 is a block diagram showing a conventional example. 11... line sensor, 12... variable gain amplifier, 13... analog/digital converter, 15...
...Peak hold circuit, 16...A/D converter reference voltage creation circuit, 17...Error amplifier, 18...
Gain control circuit, 21...Microprocessor, 2
3...Memory, 24...Document ID information input section, 3
4...Light amount adjustment circuit.

Claims

[Scope of claim for utility model registration] (1) A line sensor that receives reflected or transmitted light obtained by irradiating light from a light source onto a document and converts it into electricity, and amplifies the analog image signal from this line sensor. a variable gain amplifier capable of providing a gain of
A peak hold circuit that holds the peak value of the variable gain amplifier output, an analog/digital converter that converts the analog image signal from the variable gain amplifier into a digital image signal, and a full scale of the analog/digital converter. an analog/digital converter reference voltage creating circuit that creates a reference high level voltage and a reference low level voltage for setting an input voltage range; and a hold voltage of the peak hold circuit and the analog/digital converter reference voltage creating circuit. an error amplifier that compares the reference high level voltage of the variable gain amplifier with a reference high level voltage and outputs an error signal based on the voltage difference; An image reading device comprising a gain control circuit that controls an analog image signal input to a digital converter so that it falls within the full-scale input voltage range of the converter. (2) After the line sensor pre-scans the document for a predetermined number of lines, it shifts to regular reading scan, and the gain control circuit sets the gain of the variable gain amplifier to a predetermined value while the line sensor is pre-scanning. 2. The image reading device according to claim 1, wherein the gain of the variable gain amplifier is set in response to an error signal from an error amplifier when the line sensor shifts to normal reading scanning. (3) In the image reading device according to claim (1) or (2), an input means for inputting document identification information, and a gain control signal from a gain control circuit inputted from the input means, the document identification information. an image reading device, comprising: a memory for storing a document with an identification information input from the input means; and a control means for reading out a corresponding gain control signal from the memory and supplying it to a variable gain amplifier based on identification information of a document inputted from the input means. . (4) A line sensor that receives and photoelectrically converts reflected or transmitted light obtained by irradiating light from a light source onto a document; an amplifier that amplifies the analog image signal from this line sensor; and an amplifier that amplifies the analog image signal from this line sensor. a peak hold circuit that holds a peak value; an analog/digital converter that converts an analog image signal from the amplifier into a digital image signal;
An analog/digital converter reference voltage creation circuit that creates a reference high level voltage and a reference low level voltage for setting a full scale input voltage range to this analog/digital converter, and a hold voltage of the peak hold circuit and the analog /digital converter An error amplifier that compares the reference high level voltage from the reference voltage generation circuit and outputs an error signal based on the voltage difference; and an error amplifier that outputs an error signal based on the voltage difference; An image reading device comprising a light amount adjustment circuit that adjusts an analog image signal input to a digital converter so that it falls within the full-scale input voltage range of the converter. (5) In the image reading device according to claim (4), an input means for inputting document identification information, and an error signal from an error amplifier are stored with the document identification information inputted from the input means. An image reading apparatus comprising: a memory; and a control means for reading out a corresponding error signal from the memory and supplying it to a light amount adjustment circuit based on identification information of a document input from the input means.