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  Self-scanning light-emitting element array and driving method and circuit of the sameUSPTO Application #: 20070296803Title: Self-scanning light-emitting element array and driving method and circuit of the same Abstract: A method for driving a self-scanning light-emitting element array is provided in which two light-emitting elements may be illuminated simultaneously in one chip. In a self-scanning light-emitting element array including a transfer element array and light-emitting element array, a magnitude of the write signal for illuminating adjacent two light-emitting elements simultaneously is two times that of the write signal for illuminating one light-emitting element. The self-scanning light-emitting element array is composed of a plurality of self-scanning light-emitting element array chips arranged in a linear manner, and the two-phase clock pulses are applied commonly to the plurality of self-scanning light-emitting element array chips. (end of abstract) Agent: Ratnerprestia - Valley Forge, PA, US Inventors: Seiji Ohno, Shuya Ogi USPTO Applicaton #: 20070296803 - Class: 347244000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070296803. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a self-scanning element array, and a method and circuit for driving a self-scanning light-emitting element array. The present invention further relates to an optical writing head including a self-scanning light-emitting element array. BACKGROUND ART [0002] A writing head of an optical printer (hereinafter referred to as an optical writing head) is a light source for exposing a photosensitive drum and comprises a light-emitting element array. The structure of an optical printer including an optical writing head is shown in FIG. 1. An optically conductive material (photosensitive material) such as amorphous Si is provided on the surface of a cylindrical drum 2, which is rotated at printing speed. The surface of the photosensitive material is uniformly charged with an electrostatic charger 4. Then, light corresponding to a dot image being printed is projected by an optical writing head 6 onto the surface of the photosensitive material to neutralize the charge on the area to which the light is projected to form a latent image. Next, a developer 8 deposits the toner on the photosensitive material surface in accordance with the charged pattern on the photosensitive material surface. A transfer unit 10 transfers the toner on a paper sheet 14 fed from a cassette 12. The toner on the paper sheet is thermally fixed by the heat applied by a fixer 16, and the paper sheet is sent to a stacker 18. Upon completion of transfer, on the other hand, the charge on the drum is neutralized over the entire surface with an erasing lamp 20, and the remaining toner is removed by a cleaner 22. [0003] The construction of the optical writing head 6 is shown in FIG. 2. This optical writing head comprises a light-emitting element array 24 and a rod-lens array 26 which is an erected image, unity magnification optical system, and the lens is adapted so as to focus on the photosensitive drum 2. [0004] The inventors of the present invention have interested in a three-terminal light-emitting thyristor having a pnpn-structure as an element of the self-scanning light-emitting device, and have already filed several patent applications (see Japanese Patent Publication Nos. 1-238962, 2-14584, 2-92650, and 2-92651.) These publications have disclosed that such a self-scanning light-emitting device has a simple and compact structure for a light source of a printer, and has smaller arranging pitch of thyristors. [0005] The inventors have further provided a self-scanning light-emitting device having such structure that a transfer portion including a transfer element array is separated from a light-emitting portion including a light-emitting element array (see Japanese Patent Publication No. 2-263668). [0006] Referring to FIG. 3, there is shown an equivalent circuit diagram of a chip of this type of self-scanning light-emitting device of 1200 dpi/256 elements. A transfer portion of the chip comprises transfer elements T.sub.1, T.sub.2, T.sub.3, . . . , and a light-emitting portion comprises light-emitting elements L.sub.1, L.sub.2, L.sub.3, . . . , both transfer elements and light-emitting elements being composed of three-terminal light-emitting thyristors. The structure of the transfer portion includes diode D.sub.1, D.sub.2, D.sub.3, . . . , as means for electrically coupling the gate electrodes of neighboring thyristors to each other. V.sub.GK is a power supply (normally 5 volts), and is connected to all of the gate electrodes G.sub.1, G.sub.2, G.sub.3, . . . of the thyristors in the transfer portion via a load register R.sub.L, respectively. Respective gate electrodes G.sub.1, G.sub.2, G.sub.3, . . . of the thyristors in the transfer portion are correspondingly connected to the gate electrodes of the thyristors in the light-emitting portion. A start pulse .phi..sub.s is applied to the gate electrode of the thyristor T.sub.1 in the transfer portion, transfer clock pulses .phi.1 and .phi.2 are alternately applied to all of the anode electrodes of the thyristors in the transfer portion, and a write signal .phi..sub.I is applied to all of the anode electrodes of the thyristors in the light-emitting portion. [0007] In the figure, reference numerals 30, 32, 34, and 36 indicate .phi.1 line, .phi.2 line, .phi..sub.I line, and power supply line, respectively. R1, R2 and R.sub.I designate current limiting resistors inserted in .phi.1 line 30, .phi.2 line 32, and .phi..sub.I line 34, respectively. R.sub.s indicates a current limiting resistor for the start pulse. [0008] The operation of this self-scanning light-emitting device will now be described briefly. Assume that as the transfer clock .phi.2 is driven to a high level, the thyristor T.sub.2 is now turned on. At this time, the voltage of the gate electrode G.sub.2 is dropped to a level near zero volt from 5 volts. The effect of this voltage drop is transferred to the gate electrode G.sub.3 via the diode D.sub.2 to cause the voltage of the gate electrode G.sub.3 to set about 1 volt which is the diffusion potential of the diode D.sub.2. On the other hand, the diode D.sub.1 is reverse-biased so that the potential is not conducted to the gate electrode G.sub.1, then the potential of the gate electrode G.sub.1 remaining at 5 volts. The turn on voltage of the light-emitting thyristor of pnpn-structure is approximated to a gate electrode potential+a diffusion potential of pn junction (about 1 volt). Therefore, if a high level of a next transfer clock pulse .phi.1 is set to the voltage larger than about 2 volts (which is required to turn-on the thyristor T.sub.3) and smaller than about 4 volts (which is required to turn on the thyristor T.sub.5) then only the thyristor T.sub.3 is turned on and other thyristors remain off-state, respectively. In this manner, on-state of transfer elements are sequentially transferred by means of two-phase clock pulses .phi.1 and .phi.2. [0009] The start pulse .phi..sub.s works for starting the transfer operation described above. When the start pulse .phi..sub.s is driven to a low level (about 0 volt) and the transfer clock pulse .phi.1 is driven to a high level (about 2-4 volts) at the same time, the thyristor T.sub.1 is turned on. Just after that, the start pulse .phi..sub.s is returned to a high level. [0010] Assuming that the thyristor T.sub.2 is in on-state, the voltage of the gate electrode G.sub.2 is lowered to almost zero volt. Consequently, if the voltage of the write signal .phi..sub.I is higher than the diffusion potential (about 1 volt) of the pn junction between gate and anode, the thyristor L.sub.2 may be turned into on-state (a light-emitting state). [0011] On the other hand, the voltage of the gate electrode G.sub.1 is about 5 volts, and the voltage of the gate electrode G.sub.3 is about 1 volt. Consequently, the write voltage of the thyristor L.sub.1 is about 6 volts, and the write voltage of the thyristor L.sub.3 is about 2 volts. It follows from this that the voltage of the write signal .phi..sub.I which can write into only the thyristor L.sub.2 is in a range of about 1-2 volts. When the thyristor L.sub.2 is turned on, that is, in the light-emitting state, the amount of light thereof is determined by the current value supplied by the write signal .phi..sub.I. Accordingly, the thyristors may emit light at any desired amount of light. In order to transfer on-state to the next thyristor in the light-emitting portion, it is necessary to first turn off the thyristor in on-state by temporarily dropping the voltage of the write signal .phi..sub.I down to zero volt. [0012] A self-scanning light-emitting element array in an optical writing head may be fabricated by arranging a plurality of chips described above in a linear manner. As apparent from the operation described above, the number of light-emitting elements which may be illuminated simultaneously in one chip is only 1. [0013] In order to make the printing speed of an optical printer fast, it is required to increase an energy exposed on a photosensitive drum. An exposure energy is a product of an optical output (which has a dimension of power) and an exposure time, so that it is required to increase an optical output or an exposure time in order to make an exposure energy large. A current applied to a light-emitting element is caused to be increased to make an optical output large, but it is not permitted to increase extremely the current due to the effect for a lifetime of the light-emitting element. On the other hand, the number of light-emitting elements which may be illuminated simultaneously in one chip is required to be increased in order to extend an exposure time, i.e. increase a light emission duty. [0014] An object of the present invention is to provide a method for driving a self-scanning light-emitting element array in such a manner that two or more light-emitting elements may be illuminated simultaneously in one chip. [0015] Another object of the present invention is to provide a self-scanning light-emitting array in which two or more light-emitting elements may be illuminated simultaneously in one chip. [0016] A diode-coupled self-scanning light-emitting element array shown in FIG. 3 is structured so as to be driven by a driver IC (Integrated Circuit) of a 5V power supply system. The voltage of a power supply for a driver IC, however, has been changed from a 5V power supply system to a 3.3V or lower power supply system, which has decreased a power consumption. It is, therefore, desirable to drive a self-scanning light-emitting element array by a 3.3V power supply system. [0017] A still another object of the present invention is to provide a method for driving a diode-coupled self-scanning light-emitting element array by a 3.3V power supply system, and a driver circuit for implementing the method. [0018] An optical writing head is composed of a light-emitting element array and a rod-lens array. When the light-emitting element array is structured by arraying a plurality of self-scanning element array chips in a linear manner with the ends of adjacent chips being butted to each other to form junctions, it is impossible to make the array pitch of light-emitting elements constant over the light-emitting element array, especially an array pitch is disordered at the junctions. In order to avoid this, the chips are arrayed in a zigzag manner with the ends of each chip being overlapped to one another to make an array pitch of light-emitting elements at the junctions of chips constant. [0019] When a printing is carried out by an optical writing head comprising such a light-emitting element array, stripes may be printed on a paper sheet at the junctions of chips. [0020] A further object of the present invention is to provide an optical writing head in which the stripes due to above-described reason are not printed on a paper sheet. [0021] A still another object of the present invention is to provide a method for arranging a rod-lens array and a light-emitting element array to implement the above-described optical writing head. DISCLOSURE OF THE INVENTION Continue reading... Full patent description for Self-scanning light-emitting element array and driving method and circuit of the same Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Self-scanning light-emitting element array and driving method and circuit of the same patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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