Abstract:
A scanning device having a cable for connecting various parts is provided. A method is provided using a differential pair of clock generated signals to cancel each other, thereby reducing electromagnetic emissions. The differential pair is characterized by each being in phase with the other with regard to frequency, and each being the reverse of the other in amplitude.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority benefit of Taiwan application serial no.91122106, filed on Sep. 26, 2002. 
     BACKGROUND OF INVENTION 
     1. Field of Invention 
     The invention pertains to the field of signal transmission. More particularly, the invention pertains to transmissions between components of a scanning device and a method using paired differential analog signals for the same. 
     2. Description of Related Art 
     The scanner is a device having functions disposed between copy machines and cameras. Scanners used to be expensive, and were almost exclusively used by specialists. Recently, due to the advancement in technology, coupled with market competition, the price of scanners has dropped. In fact, scanners have moved into the mainstream of personal computer peripherals. 
     Scanners can be divided into various categories either according to their sale price or function. Ordinarily, the scanner categories include handheld scanners, paper feeding scanners, card scanners, negative scanners, and the flat panel scanners, etc. Out of the above categories, the flat panel scanner is the most popular. The flat panel scanner is analogous to a flat glass panel. Texts or graphics are placed on top of the flat glass panel, the content of which is read by sensor. Because of simplicity of structure and ease of usage, coupled with the fact that it is highly expandable, flat panel scanners have moved into the mainstream of personal computer industry. 
     Currently, because the computer interface possesses an ever-increasing speed, scanners need to possess compatible data processing speeds as well. The increased speed results in undesirable electro-magnetic interference (EMI) which is generated as a concomitant of the increased speed. 
     Referring to  FIG. 1 , a commonly known prior art scanning device  10  is shown. The scanning device  10  includes an image capturing board  102  and a mainboard  104 . By way of example, the image capturing board  102  may be a charge coupled device (CCD) board. A cable couples the image capturing board  102  to mainboard  104 . 
     The above mentioned image capturing board  102  includes an image capturing device  106  which may be CCD. The above mentioned mainboard  104  includes an analog front-end  108  (AFE), analog to digital converter  110 , and clock generator  112 . 
     The operation of device  10  is described as follows. Initially, a clock generator  112  of the image capture device  104  generates a clock signal, which is applied to the image capture component  106 . This way, the image capture component  106  is driven. Consequently, the image capture component  106  transforms an optic data signal that was captured into an analog electronic signal. At this juncture, the analog front-end  108  transforms the analog electronic signal into an analog front-end electronic signal. The analog front-end electronic signal is subject to an A/D converter  110 , wherein the analog front-end electronic signal is converted into a digital signal, and the digital signal is output. But it should be noted that clock generator  112  includes high frequency signals such as shift clock signals (φ 1 , φ 2 ), which are a pair of opposite phase signals. Opposite phase will be defined infra. It is known that opposite phase signals&#39; electromagnetic interference cancel each other. However, in scanner technology, no known electronic signal transmission uses single end mode transmission. 
     Referring to  FIG. 2 , the wave shape of a commonly known electronic signal V l  under single end mode transmission is shown. As can be appreciated, analog signal V l  has a potential level Vos. Typically the electromagnetic interference is in direct proportion to signal potential level, frequency, and transmission distance. Because signal V l  possesses high potential Vos as well as relatively high frequency and long transmission lines, the single end mode transmission can increase the electro-magnetic interference. Therefore, electro-magnetic interference can cause problems that are undesirable. Because the electro-magnetic interference can cause health problems, various jurisdictions have established standards with regard to the same. Therefore, how to reduce a scanning device&#39;s electro-magnetic interference so as to comport with the standards is important. 
     Therefore it is important to provide a scanning method and device wherein actual magnetic interference is reduced. 
     SUMMARY OF INVENTION 
     A scanning method and device are provided with the device having signals transmitting between its components. The signals cancel each other thereby reducing electromagnetic interference. 
     Accordingly, a scanning device having a differential analog transmission pair is provided. The device includes: an image capture component board and a main board. The image capture component board includes an image capture component for receiving data in the form of optic signals, and transforming the optic signals into analog electric signals, and a differential output driver coupled to the image capture component for transforming the analog electric signals into differential mode and outputting a differential analog electric signal. The main board is coupled to the image capture component board, and includes a differential input receiver for receiving the differential analog electric signal, and restoring the differential analog electric signal back to the analog electric signal. 
     Accordingly, a method for using a differential pair in a scanner is provided. The method includes the steps of receiving optic signals representing scanned data and transforming the same into analog electric signals, transforming the analog electric signals into differential analog electric signals, and receiving the differential analog electric signals and restoring the same back into analog electric signals. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a block diagram depicting a commonly known prior art scanning device. 
         FIG. 2  shows a waveform of a commonly known prior art single mold analog signal transmission. 
         FIG. 3  shows a scanning device of the instant invention. 
         FIG. 4  shows a pair of waveforms of the instant invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 3 , a scanning device  30  includes an image capture component board  302  and main board  304 . The image capture board  302  may be a CCD board. The image capture component board  302  and main board  304  are connected by cable. The image capture component board  302  includes an image capture component  306  and a differential output driver  308 . The image capture component  306  may be such components as CCD, contact image sensor (CIS), or complementary metal oxide semiconductor (CMOS). The main board  304  includes a receiver  310 , analog front  312 , analog to digital converter  314 , and clock signal generator  316 . 
     The following describes the operations of the scanner  30 . The above described image capture component  306  receives the optic signal of the scanned files. Component  306  further transforms the optic signal into an analog electronic signal. The above described differential output driver  308  transforms the analog electronic signal into differential analog electronic signals. For the waveform of the differential analog electronic signal, see  FIG. 4 . 
     Referring now to  FIG. 4 , a waveform according to the instant invention is shown. As can be seen, the differential analog electronic signal includes a signal identical to the analog electronic signal V l  of  FIG. 2 . The signal is identical in the sense that the signal possesses identical electrical potential and identical phase relationships. 
     The waveform possesses a second signal V 02  having an electric potential of −Vos. The second signal V 02  possesses identical in block reverse phase in relation to V 01 . Because the instant combined potential of both signals is zero, the electromagnetic interference is cancelled, facilitating transmission between the components such as differential output driver  308  and the receiver  310 . 
     Furthermore, the analog signal V 01  may be of the same phase as that of V l  of  FIG. 1 , but the electric potential of V 01  is the potential of V l  plus a bias potential. V 02  has the same phase but opposite polarity as that of V 01 . Alternatively, signal V 01  may have the same phase relationship as that of the signal V l , but the electric potential of signal V 01  is the difference of the potential of V l  and the bias potential. In other words, the potential of V 01  equals to the potential of V l  minus the bias potential, and V 02  is the reverse of V 01 . 
     The differential input receiver  310  receives the differential analog electronic signals and transforms them back into an analog electronic signal. The analog front  312  is used to transform the analog electronic signal into an analog front signal. The analog to digital converter  314  is used to convert analog signals into digital signals. The clock generator  316  is used to provide the clock signals to the image capture component  306 , to thereby drive the same. 
     Turning now to the operation of the scanning device  30 , the first clock signal generator  316  provides the clock signals to the image capture component  306 , thereby driving the same. Next, the image capture component  306  as disclosed receives scanned data in the form of optic signals and converts the same to analog electronic signals. The differential output driver  308  transforms the analog electronic signals into a differential mode and transmits at least one pair of differential signals. Furthermore, the differential input receiver  310  receives the at least one pair of differential signals and converts the differential signals into an analog signal. Following this, the analog front  312  transforms the analog signal into an analog front signal and uses the analog to digital converter  314  to transform the analog front signal into a digital signal. The digital signal is then output. 
     As can be appreciated, the instant invention changes the transmission mode of signals from the original analog electronic signal into a differential pair mode, thereby using the pairing to cancel electromagnetic interference. Specifically, the instant invention changes the transmission mode of signals going from the image capture component board  302  to the main board  304 . In other words, based on the notion of using a differential pair generated by a scanning device, for example by clock generator  316 , canceling each other out, electromagnetic noise is cancelled as well. 
     Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.