Abstract:
A scanning circuit having rearranged circuit modules at each end of a flat cable. After the rearrangement, the flat cable carries scanning control signals produced by a conventional IC communication interface instead of timing signals and carries digital image data instead of easily distorted and interfered analog image signals.

Description:
BACKGROUND OF INVENTION 
     1. Field of Invention 
     The present invention relates to a scanner. More particularly, the present invention relates to scanning circuit structure. 
     2. Description of Related Art 
     In recent years, rapid progress in digital technologies has lead to the development of Internet and multimedia systems. Accompanying this trend, a large number of analog images are routinely converted into a digital format to facilitate processing. A digital camera (DC) is used to extract an image from an actual scene. Similarly, an optical scanner is used to extract textual data from a document or image data from a picture. The extracted data is converted into a digital format so that a computer or electronic equipment may display an image, carry out an optical character recognition, edit the data, store up the data or simply output to some devices. 
     According to the method of inputting document image, optical scanners may be classified as a palmtop scanner, a sheet feed scanner, a drum scanner or a flatbed scanner.  FIG. 1  is a diagram showing the circuit structure of a conventional scanner. As shown in  FIG. 1 , the circuit includes an optical sensor circuit module  120  and a main circuit module  110 . Each circuit module is fabricated on a printed circuit board. The circuit modules  110  and  120  communicate with each other through a flat cable  130 . In general, the main circuit module  110  is fixed inside the lower casing of a scanner while the optical sensor circuit module  120  is attached to a scanning module capable of moving longitudinally. The optical sensor circuit module  120  has a charge-coupled device  140  therein. The charge-coupled device  140  can sense the light reflected from the image within a scan document to produce analog image signals. The analog image signals are transmitted to the main circuit module  120  by a form of analog voltage signals through the flat cable  130 . The main circuit module  120  processes the analog image signals and converts the analog image signals into digital image data, so as to provide a user to retrieve the digital image data file to carry out various operations including image display, optical character recognition, editing, data archiving or data transfer through a computer or other electronic device. In addition, to capture the image produced by the reflected light while scanning the document, the charge-coupled device  140  must receive timing control signals from the main circuit module  120  as well. Hence, the flat cable  130  must carry both timing control signals and analog image signals. 
     When demand for image quality is low, a flat cable is adequate because the quantity of image data that needs to be transferred is small. However, due to rapid expansion of computer power, the production of a high-quality scan image at a shorter scan period is always in demand. Eventually, to meet these demands, the flat cable has to carry greater quantities of analog image signals and timing control signals. In other words, the flat cable not only has to transmit signal at a higher rate, but also has to increase the number of transmission lines for transmitting timing control signals. The additional transmission lines for carrying control signals may cause electromagnetic interference (EMI) of analog image signals. Ultimately, image data may be distorted. 
     SUMMARY OF INVENTION 
     Accordingly, one object of the present invention is to provide a scanning circuit structure for a scanner capable of reducing distortion during high-speed image signal transmission so that electromagnetic interference is minimized and quality of transmitted image is improved. 
     To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a scanning circuit structure for a document scanner. The scanning circuit includes a main circuit module and an optical sensor circuit module. The main circuit module receives a scanning instruction from a communication interface and converts the scanning instruction into scan control signals. The scan control signals are passed to a connection cable. In the meantime, the main circuit module also receives digital image data of a scan document from the connection cable. The optical sensor circuit module is connected to the main circuit module via the connection cable. The optical sensor circuit module receives the scan control signals and converts the scan control signal into timing control signals. Hence, operations including the scanning of a document, the extraction of an analog image signal and the conversion of the analog image signal into a digital image data are executed in sequence. 
     In one embodiment of this invention, the main circuit module includes a main control logic unit, a memory unit and a memory control logic unit. The optical sensor circuit module includes an optical sensor, an analog front-end processor, an analog/digital converter and a timing signal generator. The main control logic unit in the main control module receives scanning instructions and converts the instructions into scanning control signals. The main control logic also receives digital image data scanned from a document. The memory unit stores digital image data. The memory control logic unit is coupled to the main control logic unit and the memory unit for controlling the access of digital image data. The optical sensor inside the optical sensor circuit module is used to sense an analog image signal that is formed by the light reflected from the document. The analog front-end processor is coupled to the optical sensor for pre-processing the analog image. The analog/digital converter is coupled to the front-end processor for converting the pre-processed analog image signal into digital image data. The timing signal generator is coupled to the optical sensor and the analog/digital converter for producing timing control signals, so as to control the scanning process on the document, produce the analog image signal of the document, and convert the analog image signal into the digital image data. 
     The main control logic unit in this invention also includes an image front-end processor for compensating and adjusting the captured digital image data so that the scanned image has a better quality. In general, the memory unit contains dynamic random access memory and the optical sensor is a charge-coupled device (CCD) or a CMOS image sensor. The connection cable linking the main circuit module and the optical sensor circuit module include a flat cable and the scanning circuit interfaces with a computer through a universal serial bus (USB). The scanning control signals are transmitted through an IIC or 3-wire IC communication interface. 
     In this invention, digital image data are transmitted instead of analog image signals. Furthermore, the scanning control signals are transmitted through a common IC communication interface instead of timing control signals transmitted through a connection cable. Through this arrangement, image data distortion due to high-speed transmission is greatly minimized. Hence, electromagnetic interference is minimized and quality of image transmitted by the scanner is improved. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
         FIG. 1  is a diagram showing the circuit structure of a conventional scanner; and 
         FIG. 2  is a diagram showing the circuit structure of a scanner according to one preferred embodiment of this invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
       FIG. 2  is a diagram showing the circuit structure of a scanner according to one preferred embodiment of this invention. As shown in  FIG. 2 , the scanning circuit  200  is responsible for controlling the entire process of scanning a document. The scanning circuit  200  includes a main circuit module  210  and an optical sensor circuit module  220 . The main circuit module  210  and the optical sensor circuit module  220  are linked together through a connection cable  230  such as a flat cable. The flat cable carries both scan control signals and digital image data. The main circuit module  210  further includes a main control logic unit  270 , a memory unit  280  and a memory control logic unit  275 . The optical sensor circuit module  220  further includes an optical sensor  240 , an analog front-end processor (AFE)  250 , an analog/digital converter  260  and a timing signal generator  265 . 
     The main control logic unit  270  in the main circuit module  210  connects with the human/machine interface of a personal computer (not shown) through a communication interface  285 . Here, the communication interface  285  can be a universal serial bus (USB) interface or an enhanced parallel port (EPP) interface, for example. The communication interface  285  receives important scanning instructions regarding image resolution, brightness level and scanning range and converts the scanning instructions into scanning control signals that pass along the connection cable  230 . 
     When the optical sensor circuit module  220  receives scanning control signals from the main circuit module  210 , the timing generator  265  produces the required timing control signals for extracting an analog image signal from the optical sensor  240 . The optical sensor  240  is a charge-coupled device (CCD) or a CMOS image sensor, for example. The captured analog image signal is preprocessed by the analog front-end preprocessor  250 . Thereafter, the pre-processed analog image is transmitted to the analog/digital converter  260  and converted to digital image data. The digital image data is subsequently transmitted to the main circuit module  210  through the connection cable  230 . At this moment, the data transmitted on the connection cable  230  is no longer the analog signal that easily has the distortion but is the digital image data that can be easily transmitted in a fast speed. As a result, it can effectively solve the issue about difficulty on maintaining the scanning quality when the scanning process is operated in the fast speed. 
     On receiving the digital image data, the main circuit module  210  transfers the data to the memory unit  280  via the memory controller  275 . The memory unit  280  may contain conventional types of memory such as synchronous or non-synchronous dynamic random access memory (DRAM) or static random access memory (SRAM). Obviously, the main control logic unit  270  may incorporate an image preprocessor (not shown) for compensating and adjusting the captured digital image data so that the scanned image can have better quality. In addition, timing signals may have to be adjusted due to the change in connection between the communication interface of various integrated circuits (ICs). 
     In conclusion, major advantages of this invention include: 
     1. Since the flat cable transmits digital data instead of easily distorted analog image signals, a clearer image can be obtained at a higher scanning speed. 
     2. Since the flat cable transmits scanning control signals between conventional IC communication interfaces instead of timing control signals, the effect due to electromagnetic interference is greatly minimized. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.