Active matrix liquid crystal light valve with driver circuit

Abstract: A technology is disclosed in which the voltage of a drive signal pulse to be supplied to a switch, which transfers a signal to be supplied to a liquid crystal cell, is raised. A plurality of lines for the signals to be supplied to a switch array which transfers the signal to be supplied to the liquid crystal cell is provided so as to supply drive signal pulses for operating switches which correspond to a plurality of the lines while time sequentially overlapping the drive signal pulses.

Description: The present invention relates to an active matrix liquid crystal light valve (AMLCV). Hitherto, active matrix liquid crystal light valves of twisted nematic (TN) liquid crystal type have been marketed as flat panel displays or as projection TV monitors. Each active element typified by a thin film transistor (TFT), or a diode or a MIM (Metal Insulator Metal Element) enhances the optical switch response of TN liquid crystal material which suffers from relatively slow response, by keeping a state, in which the TN liquid crystal material is being applied with voltage, for a period longer than the actual line selection period. Furthermore, the active elements cause liquid crystal devices including TN liquid crystal having no memory characteristics (self-holding characteristics) to have a substantial memory state for each unit cell for one frame by maintaining the aforesaid voltage applied state. The AMLCV has excellent display characteristics because it is theoretically freed from crosstalk between lines and between pixels thereof. Recently, ferroelectric liquid crystal (FLC) materials having response speeds orders of magnitude higher than those of TN liquid crystal materials have been developed and incorporated in active matrix liquid crystal light valves. In the aforesaid circumstances, there is a possibility that a further excellent display device can be obtained by driving the FLC by the active matrix device. An active matrix liquid crystal light valve combining FLC and TFTs has been disclosed in, for example, U.S. Patent No. 4,840,462 and in Proceedings of the SID, vol. 30, 1989 "Ferroelectric Liquid-Crystal Video Display" vol. 30, 1989. Fig. 9 illustrates a conventional liquid crystal display circuit. The circuit shown in Fig. 9 comprises a unit pixel composed of a common electrode COM, a liquid crystal cell 701 filled with liquid crystal material between a pixel electrode CE and the common electrode COM, and a pixel TFT 702. The circuit still further comprises a signal line 703, a line buffer 704, a shift pulse switch 708, and a horizontal shift register 705 for transmitting video signals. The circuit further comprises a gate line 711 and a vertical shift register 706 for transmitting gate signals. The video signals are received by a signal input terminal and line 707 so as to be sequentially transferred to each pixel or each line of pixels while having their timing shifted. Fig. 10 illustrates the timing of drive pulses for use in the conventional active matrix liquid crystal display device shown in Fig. 9. Fig. 10 illustrates the timing of the drive pulses for use in a line sequential drive method. That is, video signal Sv to be recorded on the liquid crystal is recorded in such a manner that video signals for one line are stored in the line buffer via a shift pulse switch 708 which is operated by the horizontal shift register 705 arranged to transmit an output in synchronization with the frequency of the video signal Sv. After the video signals for all of the pixels for one line have been stored in the line buffer 704, the video signal is transferred to each liquid crystal cell via a respective pixel switch, which has been switched on by an output switch of the line buffer 704 and the vertical shift register 706. The signals are usually transferred to each liquid crystal cell during a blanking period of a horizontal scanning period or transferred collectively to a certain horizontal line in response to pulse t. At the aforesaid timing, the video signals are sequentially transferred to each line. When molecules of the liquid crystal, which form each cell, move in accordance with the voltages of the signals thus transferred, the transmittance of the respective liquid crystal cells, which are arranged between crossed polarizers, is changed. The aforesaid state is shown in Fig. 11. The voltage of the signal shown in the axis of abscissa of Fig. 11 depends upon the type of liquid crystal. For example, the values are defined to be effective voltage values (V rms ) in the case of a TN liquid crystal material. The qualitative description of the aforesaid value will be made with reference to Fig. 12. In order to prevent DC components being applied to the liquid crystal for a long time, there is a method in which the polarity of the signal voltage is altered for each frame at the time of supplying the signal. In this case, the liquid crystal acts in accordance with the AC voltage component shown by a portion designated by diagonal line shading. Therefore, execution voltage v rms is expressed as follows when the time for two frames is tF and the signal voltage to be transferred to the liquid crystal is V LC (t) : On the other hand, an FLC light valve is ordinarily driven by DC voltage. In a case where FLC of a type having a bistable state is employed (it is preferable that chiral smectic liquid crystal be used, further preferable chiral smectic liquid crystal such as phase C (SmC*), phase H (SmH*), SmI*, SmF* or SmG* chiral smectic liquid crystal be used), drive waveforms shown in Fig. 13 are supplied. That is, the signal voltage is reset to either of the bistable states in accordance with reset voltage VR before the signal is written, and then writing voltage signal (VM) is applied. Also the signal voltage contributing to the transmittance shown in Fig. 11 is designated by diagonal line shading. In a manner different from the TN liquid crystal, the DC component of the writing voltage is the signal voltage as it is. Although the voltage of the pixel electrode is changed in accordance with the signal voltage if the drive method shown in Fig. 10 is used, it is always positive with respect to the potential of the common electrode of the liquid crystal similarly to the case where a DC voltage component is always applied to the liquid crystal cell. In the case where the TN liquid crystal is used as the liquid crystal material, the aforesaid DC component causes a problem to arise in that the liquid crystal molecules can be"burnt", i.e. can decompose. Methods of removing the DC voltage component is typified by a method of reversing the signal voltage for each frame arranged as shown in Fig. 12. The signal voltage at the N-th time is so applied as to be positive with respect to the potential of the common electrode, while the signal voltage at the (N + 1)-th time is so applied as to be negative. By reversing the polarity of the signal voltage with respect to the potential of the common electrode for each frame as described above, the DC voltage components to be applied to the liquid crystal cell are set off so that burning of the liquid crystal molecules can be prevented. Similarly, a method of reversing the same for each line interval 1H and a method of reversing the same for each pixel may be employed. However, the aforesaid reversing drive method gives rise to the following problems. Assuming that the maximum value of the signal voltage is V MAX , the shift register portion must have, regardless of the type of the reversing method, a performance capable of transferring a signal having an amplitude which is twice VMAX if the reversing drive method is employed. Therefore, the shift register must, of course, be able to withstand the ON/OFF voltage. As a means for relaxing the required condition for the voltage resistance, it might be feasible to employ a method in which the maximum amplitude of the signal voltage is reduced. However, the aforesaid means cannot be adapted for high definition display which is expected to be widely used in the future and which must have excellent precision because it is difficult to keep the gradation as can be understood from Fig. 11. Another method can be employed in which voltage-resisting MOS transistors such as LDD (Lightly Doped Drain) serving as switches are used as transistors of the shift register. However, the aforesaid voltage-resisting MOS transistors, which are being developed currently, give rise to a problem in that the mutual conductance (gm) is lowered due to increase in the resistance, which is applied in series to the source and the drain although it is able to improve the voltage resistance. As described above, the AMLCV must be driven at a higher speed in the case of high definition vision display. Therefore, the TFT must have a larger conductance gm. What is worse, the MOS transistor, having the voltage resistance as described above, can be manufactured only by a complicated process, causing problems to arise in that the yield deteriorates when it is used to constitute the shift resistors and that the manufacturing cost cannot be reduced. To summarise, there is a current requirement to provide an active matrix liquid crystal light valve having response to a wider dynamic range of image signal. It has been a problem meeting the requirement without a costly resort to using a shift register having a higher than customary voltage resistance. The present invention, defined in the appended claims, is intended to provide a solution to this problem. It is acknowledged that a voltage raising sub-circuit including a capacitor and a pre-charging transistor, connected to the capacitor, is disclosed in EP-A-0404025. The sub-circuit described therein is arranged between a shift register and the scan selection lines of an active matrix liquid crystal light valve. The scan-lines are driven from one or other of the register clock signal lines, via respective drive transistor switches, the gates of which are connected to the outputs of a respective voltage raising sub-circuit. EP-A-0293156 discloses a scan circuit for scanning a solid-state image pick-up apparatus which also is driven from one or other of the register clock signal lines. In preferred embodiments of the present invention successive sub-circuits are connected to the shift register with a one output terminal stagger and the transistor switches at the output of each sub-circuit are connected to respective colour signal lines. The switching pulses at the output of successive sub-circuits overlap, the precharge voltage pulse of each coinciding with the full voltage pulse of each preceding sub-circuit. Fast switching is thus facilitated. It is acknowledged that it is known to apply scan line signal pulses which have an overlap. Examples are disclosed in US-A-4724433 and GB 2146478. US-A-5061920 discloses an active matrix liquid crystal display in which the signal line drive circuitry is modified. Signals provided from the output terminals of a shift register, are latched, demultiplexed and level shifted prior to being applied to the signal line driver transistor switches. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates a drive circuit for use in an active matrix liquid crystal light valve according to Embodiment 1 of the present invention; Fig. 2 is an operation timing chart of the drive circuit according to Embodiment 1 of the present invention; Fig. 3 is a timing chart for the drive circuit according to Embodiment 1 and partially using a PMOS transistor; Fig. 4 illustrates a drive circuit for use in an active matrix liquid crystal light valve according to Embodiment 2 of the present invention; Fig. 5 is an operation timing chart of the drive circuit according to Embodiment 2 of the present invention; Fig. 6 illustrates a drive circuit for use in an active matrix liquid crystal light valve according to Embodiment 3 of the present invention; Fig. 7 is an operation timing chart of the drive circuit according to Embodiment 3 of the present invention; Fig. 8 is a schematic view which illustrates the structure of an image information processing apparatus incorporating a liquid crystal light valve embodying the present invention; Fig. 9 illustrates a circuit for a conventional active matrix liquid crystal display; Fig. 10 illustrates the timing of drive pulses for the active matrix liquid crystal display; Fig. 11 is a graph which illustrates the correlation between the transmittance of a TN liquid crystal cell and signal voltage; Fig. 12 illustrates a drive waveform for an active matrix liquid crystal display which uses a TN liquid crystal; and Fig. 13 illustrates a drive waveform for an active matrix liquid crystal display which uses a ferroelectric liquid crystal; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is arranged in such a manner that the voltage of drive signal pulses, supplied to each switch for transferring a signal to be applied to a liquid crystal cell, is raised. As a result of the aforesaid structure, a complicated structure required to improve the voltage resistance of transistors which constitute the shift register can be omitted. Devices having excellent performance can be manufactured while maintaining an excellent yield. The present invention can be used in liquid crystal printers, light valves for liquid crystal displays, and image processing apparatuses on which the aforesaid light valves are mounted. The active element, the transferring switch, the shift register and the voltage-raising means are preferably integrally formed on one substrate. It is preferable that the substrate has a semiconductor region on an insulating film thereof. The reason for this lies in that use of the substrate of the aforesaid type enables a light transmissive type liquid crystal light valve including a peripheral circuit to be formed easily. A plurality of the lines may be arranged to receive a plurality of element signals which constitute the video signal, the element signal being synthesized so as to be one video signal. In particular, use of colour component signals such as a red signal, a green signal and a blue signal as the component signals enables the signal processing speed for forming a complicated colour image to be easily raised. Preferred embodiments of the present invention will now be described in detail. The description that follows is given by way of example only. (Embodiment 1) Fig.1 illustrates a drive circuit for use in an active matrix device according to this embodiment. Referring to Fig. 1, reference numeral 101 represents a shift register, and P1 to P7 represent output terminals of the shift register 101. Reference numeral 102 represents a first MOS transistor having the gate and the source which are connected to the first output terminal P1 of the shift register 101. Reference numeral 103 represents a first capacitor having a first electrode connected to the second output terminal P2 of the shift register 101. Reference numeral 104 represents a second MOS transistor having the gate connected to the third output terminal P3 of the shift register 101 and having the source connected to a reset power supply line 105 connected to a reference power source V RS for supplying resetting reference voltage. The drain of the first MOS transistor, the second electrode of the first capacitor 103 and the drain of the second MOS transistor are connected to one another so as to be a first output terminal 01. A structure constituted similarly to that described above, the MOS transistor and the capacitor are connected to the third output terminal P3, the fourth output terminal P4 and the fifth output terminal P5 of the shift register so as to be a second output terminal 02. Then, connections are performed similarly to the description above while performing shifting by a degree of two terminals. Reference numeral 106 represents a switching transistor which is controlled in response to a signal from the shift register 101. The specific operation will now be described with reference to an operation timing chart shown in Fig. 2. The outputs from the shift register 101 are, as can be understood from P1 to P7 shown in Fig. 2, sequentially transmitted from the corresponding terminals while being freed from overlap in terms of time. The potential of the output terminal 01 is first raised to a level which is lower than the output voltage from P1 by a degree corresponding to the threshold value of the MOS transistor 102. In response to the signal from P2, the potential is then raised by a degree corresponding to the voltage which is the result of multiplication of the signal voltage P2 and the capacitance division ratio between the capacitor 103 and the gate capacity of the transistor 106 via the capacitor 103. Assuming that the output amplitude of P1 to P7 is 7V, the threshold voltage of the first MOS transistor 102 is 1V and the capacitance division ratio of the gate capacity of the capacitor 103 and that of the transistor 106 is 0.9, the voltage to be applied to the gate of the switching transistor 106 is, as expressed by the following equation, raised to 12.3 V, which is 1.76 times the operation voltage 7 V of the shift register 101. Output terminal voltage = (7 - 1) + 7 x 0.9 = 12.3 V The circuit thus arranged is able to generate a high voltage level of 12.3 V while keeping the power supply voltage in the shift register 101 and to be applied to each transistor in this circuit at the aforesaid low level of 7 V. Therefore, a signal, the amplitude of which is 11V, can be treated. A timing chart realized in the case where a PMOS is used as the switching transistor 106 is shown in Fig. 3. If the PMOS is used, a similar effect can be obtained. (Embodiment 2) Fig.4 illustrates a circuit for use in a second embodiment. This embodiment is arranged in such a manner that the circuit according to the present invention is connected to the first output terminal P1, the second output terminal P2 and the third output terminal P3 of the shift register, and then the same is sequentially connected to the second output terminal P2, the third output terminal P3 and the fourth terminal P4 while being shifted by a degree of one terminal. The operation timing of this circuit is shown in Fig. 5. As can be understood from Fig. 5, outputs from the circuit according to this embodiment are overlapped for a certain period, so that operation speed can be raised in comparison to Embodiment 1 by overlapping the timing of the outputs in the case where a plurality of signal lines are connected by the switching transistors 106, for example in a case where signal lines corresponding R, G and B are used in a color panel. (Embodiment 3) Fig. 6 illustrates a circuit for use in a third embodiment. According to Embodiments 1 and 2, the period in which a desired high potential can be maintained is limited to the period in which the signal P2 is outputted. However, this embodiment enables the potential of the first electrode of the capacitor to be maintained as shown in Fig. 7 although the output of the signal P2 has been ended and also the potential of the output from the second electrode can be maintained at a desired high level until the next signal P3 is supplied by arranging the structure in such a manner that a third MOS transistor 601 is inserted into a portion between the first electrode of the first capacitor and the output terminal P2 of the shift register, the source and the gate of the aforesaid MOS transistor are connected to the output terminal P2 and the drain of the same is connected to the first electrode of the first capacitor. As a result, the period in which the switching transistor is able to transfer the signal can be lengthened. A reset transistor 602 is connected to the first electrode of the first capacitor, so that the potential of the first electrode is reset when the signal P3 is supplied. The output (the video signal) from the switching transistor 106 according to the aforesaid Embodiments 1 to 3 is supplied to the signal line 703 via the line buffer 704 shown in Fig. 9 in the case where a line sequential drive method is employed. In another case where driving is sequentially performed in a time sequential manner for each pixel, the output is supplied directly to the signal line 703, i.e. the output does not pass through a line buffer. The circuit according to Embodiments 1 to 3 is formed on a semiconductor substrate. Fig. 8 is a schematic view which illustrates an image information processing apparatus which employs the AMLCD according to the present invention. Reference numeral 1 represents an AMLCD having a display portion 5 formed at the central portion of a substrate 6 thereof. Fig. 8 is a partially enlarged view of the pixel portions given reference numerals 4 and 4'. A drive circuit including the shift register is disposed around the display portion 5. Horizontal drive circuits 3 and 3' are connected to the signal lines 703 and arranged to supply video signals. The horizontal drive circuits 3 and 3' respectively are disposed above and below the display portion. Vertical drive circuits 2 and 2' for generating line selection signals are disposed to the right and left of the display portion 5. The AMLCD 1 is structured in such a manner that the aforesaid drive circuits are connected to drive control circuit 10 mounted on an individual substrate. The drive control circuit 10 includes a circuit for dividing one video signal into a plurality of element signals (for example, S VR , S VG and S VB ) in a case where it is designed to be adapted to Embodiments 2 and 3. The drive control circuit 10 is, together with a lighting control circuit including a power source 12 and an inverter for controlling lighting of the light source, connected to a central processing circuit 14. The image information processing apparatus according to this embodiment further comprises an optical system 22 including a lens through which image information is received, an image sensor 21 including a photoelectric conversion element and its drive circuit 20. In addition, image information obtained by the image sensor 21 and/or displayed image information are recorded to a recording medium by a recording control circuit 30 including a recording head 31. The active matrix liquid crystal display 1 can be formed on one substrate while including the liquid crystal device, the liquid crystal drive circuit and its peripheral drive circuit by using a semiconductor substrate having a single crystal Si layer and manufactured by the following method. The method will now be described. The single crystal Si layer of the semiconductor substrate is formed by using a porous Si substrate obtained by making a single crystal Si substrate to be porous. As a result of an observation performed by using a transmissive type electronic microscope, the porous Si substrate have pores, the mean diameter of which is about 600Å formed therein. Furthermore, although the density is less than the half of that of the single crystal Si, single crystallinity is maintained. Therefore, a single crystal Si layer can be allowed to epitaxial-grow on a porous layer. However, the formed pores are again arranged if the temperature is higher than 1000°C, causing the characteristics of the acceleration etching to be lost. Therefore, it is considered preferable to cause the Si layer to epitaxial-grow by a molecular beam epitaxial grow method, a plasma enhanced CVD method, a thermal CVD method, a photo CVD method, a bias sputtering method or a liquid-phase crystal growth method. A method of allowing the single crystal layer to epitaxial-grow after a P-type Si has been made to be porous type will now be described. First, a Si single crystal substrate is prepared, and it is made to be a porous type by an anode forming method in which a HF solution is used. Although the density of the single crystal Si is 2.33 g/cm 3 , the density of the porous Si substrate can be changed to 0.6 to 1.1 g/cm 3 by changing the concentration of the HF solution to 20 wt% to 50 wt%. The porous layer can easily be formed in the P-type Si substrate because of the following reasons: The porous Si was found during research of electrolytic polishing. In a dissolution reaction of Si in the anode formation, the anode reaction of Si in a HF solution requires positive holes, the anode reaction being expressed as follows: Si + 2HF + (2 - n) e + → SiF 2 + 2H + + ne - SiF 2 + 2HF → SiF 4 + H 2 SiF 4 + 2HF → H 2 SiF 6 or Si + 4HF + (4 - λ) e + → SiF 4 + 4H + + λe - SiF 4 + 2HF → H 2 SiF 6 where e + and e - respectively denote a positive hole and electron, and n and λ respectively denote the number of positive holes required to dissolve one Si atom. If n > 2 or λ > 4, the porous Si can be formed. Therefore, it can be said that the P-type Si having the positive holes can easily be made to be the porous type. Another fact that a high density N-type Si can be made to be a porous type has been reported. Hence, the porous Si can be made to be the porous type regardless of the type of the Si. Since the porous layer has a large quantity of gaps formed therein, its density is reduced to the half or less. As a result, the surface area significantly increases as compared with the volume, causing the speed, at which it is chemically etched, to be raised considerably in comparison to the speed at which an ordinary single crystal layer is etched. Then, the conditions for making the single crystal Si to be porous type by anode forming will now be described. It should be noted that the starting material to form the porous Si by anode forming is not limited to the single crystal Si, but Si of a type having another crystal structure may be employed. Applied voltage: 2.6 V Current density: 30 mA·cm -2 Anode forming solution: HF:H 2 O:C 2 H 5 OH = 1:1:1 Time: 2.4 hours Thickness of porous Si: 300 µm Porosity: 56% Then, Si is allowed to epitaxial-grow on the porous Si substrate thus formed, so that a single crystal Si thin film is formed. It is preferable that the thickness of the single crystal Si thin film be 50 µm or less, more preferably 20 µm or less. Then, the surface of the single crystal Si thin film is oxidized, and a substrate which finally forms the substrate is prepared, and the oxidized film on the surface of the single crystal Si and the aforesaid substrate are bonded to each other. As an alternative to this, the surface of a single crystal Si substrate is oxidized, and it is bonded to the single crystal Si layer. The reason why the aforesaid oxidized film is formed between the substrate and the single crystal Si layer lies in that the interfacial level generated from the base interface of a Si active layer can be lowered in the oxidized layer interface as compared with the aforesaid glass interface in the case where glass is used as the substrate and therefore the characteristics of the electronic device can be significantly improved. As an alternative to this, only a single crystal Si thin film, from which the porous Si substrate has been removed by selective etching, may be bonded to a new substrate. Although the aforesaid members can be bonded closely due to van der Waals force simply by making them come in contact with each other at the room temperature after their surfaces have been cleaned, they are heated at a temperature of 200 to 900°C under nitrogen atmosphere, preferably 600 to 900°C. Then, a Si 3 N 4 layer is deposited on the overall surface of the two substrates bonded so as to serve as an etching prevention film, and only the Si 3 N 4 layer formed on the surface of the porous Si substrate is removed. An apiezon wax may be used in place of the aforesaid Si 3 N 4 layer. Then, the porous Si substrate is completely removed by etching or the like, so that the semiconductor substrate having the thin film single crystal Si layer can be obtained. Then, a selective etching method for electroless- and wet-etching only the porous Si substrate will now be described. As etching liquid which does not etch crystal Si but which is able to selectively etch only the porous Si, any of the following materials can be preferably employed: buffered hydrofluoric acids such as a hydrofluoric acid, an ammonium fluoride (NH 4 F) and a hydrogen fluoride (HF); a mixture solution of a hydrofluoric acid or a buffered hydrofluoric acid prepared by adding a hydrogen peroxide solution; a mixture solution of a hydrofluoric acid or a buffered hydrofluoric acid prepared by adding alcohol; or a mixture solution of a hydrofluoric acid or a buffered hydrofluoric acid prepared by adding a hydrogen peroxide and alcohol. The bonded substrates are wetted with the aforesaid solution so that etching is performed. The etching speed depends upon the concentration of the hydrofluoric acid, the buffered hydrofluoric acid and the hydrogen peroxide solution and upon the temperature. By adding the hydrogen peroxide solution, the oxidation of Si is accelerated and therefore the reaction speed can be raised as compared with the method in which they are not added. Furthermore, the reaction speed can be controlled by changing the ratio of the hydrogen peroxide. By adding alcohol, bubbles of a gas generated due to the reaction taken place in the etching process can be immediately removed from the etched surface while eliminating a necessity of performing stirring. Therefore, the porous Si can be uniformly and efficiently etched. It is preferable that the concentration of HF contained in the buffered hydrofluoric acid be ranged from 1 to 95 wt%, preferably from 1 to 85 wt%, and more preferably from 1 to 70 wt%. It is preferable that the concentration of NH 4 F contained in the buffered hydrofluoric acid be ranged from 1 to 95 wt%, preferably from 5 to 90 wt%, and more preferably from 5 to 80 wt%. It is preferable that the concentration of HF with respect to the etching solution be ranged from 1 to 95 wt%, preferably 5 to 90 wt% and more preferably from 5 to 80 wt%. The concentration of H 2 O 2 with respect to the etching solution be ranged from 1 to 95 wt%, preferably 5 to 90 wt%, and more preferably 10 to 80 wt% while offering the effect of the hydrogen peroxide solution. The concentration of alcohol with respect to the etching solution be 80 wt% or less, preferably 60 wt% or less, and more preferably 40 wt% or less while offering the effect of the alcohol. It is preferable that the temperature be 0 to 100°C, preferably 5 to 80°C, and more preferably 5 to 60°C. The alcohol for use in the process according to this embodiment is not limited to ethyl alcohol, but it may be alcohol such as isopropyl alcohol which does not arise a practical problem during the manufacturing process and which enables the effect required for the added alcohol to be obtained. The semiconductor substrate thus obtained has the single crystal Si layer formed similarly to that of an ordinary wafer in such a manner that it is flattened and thinned to have a large area on the overall surface of the substrate. The single crystal Si layer of the semiconductor substrate is separated by a partial oxidation method or by etching so as to be formed into an island, so that impurities are doped and a p- or n-channel transistor is formed.

Claims: An active matrix liquid crystal light valve having a drive circuit (101-106) arranged for applying a video signal to the respective signal lines (703) of said light valve (1), wherein said drive circuit (101-106) comprises: a shift register (101); a video signal input (707); a plurality of MOS transistor switches (106) connected to said input (707) and arranged to be controlled by said shift register (101); respective voltage raising sub-circuits (102-105) interposed between said shift register (101) and respective ones (01,02,03,...) of said MOS transistor switches (106), each sub-circuit (102-105) comprising: a respective first MOS transistor (102) the gate and source of which are connected to a respective first output terminal (P1,P3,P5; P1,P2,P3) of said shift register (101); a respective capacitor (103), a first electrode of which is connected to a respective second output terminal (P2,P4,P6; P2,P3,P4) of said shift register (101), said respective second output terminal being the terminal immediately following said respective first output terminal; and a respective second MOS transistor (104), the source of which is connected to a common reset power supply line (105), the gate of which is connected to a respective third output terminal (P3,P5,P7; P3,P4,P5) of said shift register (101), said respective third output terminal being the terminal immediately following said respective second output terminal, and the drain of which is connected to the drain of said respective first MOS transistor (102), the second electrode of said respective capacitor (103), and the gate of the respective one (01,02,03,...) of said MOS transistor switches (106). A light valve according to claim 1 wherein: said plurality of MOS transistor switches (106) are connected to a single-line video signal input (707) to switch the video signal (S v ); and the respective first output terminals (P3,P5), connected to the source and gate of the respective first MOS transistors (102) of successive respective sub-circuits (102-105), are the same output terminals as the respective third output terminals (P3,P5) connected to the gate of the respective second MOS transistors (104) of the immediately preceding respective sub-circuits (102-105). A light valve according to claim 1 wherein: respective first, second and third ones (01,02,03) of said plurality of MOS transistor switches (106) are connected to respective lines of said video signal input (707) to switch respective colour component signals (S VB ,S VG ,S VR ) of the video signal (S V ); and the respective first output terminals (P2,P3) connected to the source and gate of the respective first MOS transistors (102) of successive respective sub-circuits (102-105), are the same output terminals as the respective second output terminals (P2,P3) connected to the first electrode of the respective capacitors (103) of the immediately preceding respective sub-circuits (102-105). A light valve according to claim 3 wherein in each respective sub-circuit (102-105): a respective third MOS transistor (601) is interposed between the respective capacitor (103) and said shift register (101), the source and gate thereof being connected to the respective second output terminal (P2,P3,P4) of said shift register (101), and the drain thereof being connected to the first electrode of the respective capacitor (103); and a respective fourth MOS transistor (602) interposed between the respective capacitor (103) and the respective second MOS transistor (104), the source thereof being connected to the drain of the respective third MOS transistor (604) and the first electrode of the respective capacitor, the gate thereof being connected to the respective third output terminal of said shift register (101), and the drain thereof being connected to the source of the respective second MOS transistor (104). A light valve according to any preceding claim wherein said drive circuit (101-106) includes: a line buffer (704), the inputs of which are connected to said plurality of MOS transistor switches (106); and a plurality of MOS transistor transfer switches (710) connected between the outputs of said line buffer (704) and the signal lines (703) of the light valve. A light valve according to any preceding claim 1 to 4 wherein said plurality of MOS transistor switches (106) are connected directly to the signal lines (703) of the light valve. A light valve according to any preceding claim wherein said shift register (101), said plurality of MOS transistor switches (106), said respective voltage raising sub-circuits (102-105) and the active elements (702) of the light valve are integrated on a common semiconductor substrate (6).

Inventors: KOUCHI TETSUNOBU, KOUCHI, TETSUNOBU, KOUCHI, TETSUNOBU, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: G09G3
IPC codes: G09G3