Abstract: An electrical circuit compensates for spatial variations in the light transmittance of the target surface (45) of an electron beam-addressed liquid crystal light valve (10). Such variations in light transmittance, which stem in part from the position dependent angle of incidence of the writing beam electrons and position dependent alignment layer variations arising out of manufacturing process limitations, affect the ability to achieve a monotonic gray scale luminance over the display surface. The compensating circuit adjusts the amount of beam current of the writing electron beam by varying the gain and offset voltage of the video signal, which modulates the writing beam current. This is accomplished by applying the X and Y scan position signals to a correction signal generator (102), which produces gain correction and offset correction signals whose magnitudes vary in response to instantaneous scan position of the writing electron beam on the target surface of a particular light valve.

Abstract: A current source provides an output current whose magnitude is substantially independent of changes in temperature. In each of three embodiments (50, 100, 120), one or more bipolar transistors are employed to provide a compensating current which is dependent on the base-to-emitter voltages, V.sub.BE, of such bipolar transistors. The compensating current changes with temperature so as to offset changes in the uncompensated output current so that the total output current is substantially independent of V.sub.BE. The three embodiments employ current mirror circuits (10, 122) that provide a current source of simple circuit design that is operable with the use of a single power supply at a relatively low voltage.

Abstract: A liquid crystal cell (40) for an electron beam-addressed liquid crystal light valve has a rigid glass substrate (16) and target substrate (44) formed of thin flexible material. The cell (40) is constructed so that the spacing between the flexible substrate (44) and the rigid substrate (16) is precisely maintained. A fixture (72) is employed for attaching the target substrate (44) to the rim (102) of the light valve body (14) prior to assembly of the cell (40).

Abstract: An analog-to-digital converter (10) comprises a set of comparators (12a-12f) for providing a set of different output signals whose logic states are a function of an analog input signal voltage and one or more reference voltage signals supplied by a resistive network (16). The comparators are connected to a decoder (20) for processing the thermometer code outputs of the comparators to generate a digital word output corresponding to the voltage amplitude of the analog signal. Several of the comparators are also connected to an error checking network (22), including a preconditioning circuit (100) and a detection circuit (102) for processing these comparator outputs to provide an error signal whenever one or more of the comparators are not operating properly. The error checking network and decoder are connected to an error correction circuit (26) for correcting the digital word signal in accordance with the error signal.

Abstract: A digital-to-analog converter circuit (10) comprises a current switch (22) that has differential input conductors (16a, 16b, . . . , 16n and 18a, 18b, . . . , 18n) which receive complementary logic voltage signals corresponding to a digital input word (X.sub.1, X.sub.2, . . . , X.sub.n). The current switch synthesizes an output signal (V.sub.o -V.sub.o) whose magnitude corresponds to the weighted value of the digital input word. The circuit further comprises a current reference source (60) that develops a reference current (I.sub.REF) from which transistor constant-current sources (48a, 48b, . . . , 48n) in the current switch derive binary-weighted currents to synthesize the output voltage signal. The current reference source includes an impedance element or resistor (70) through which the reference current flows and which is scaled to the load impedance connected to the current switch.

Abstract: A frequency-compensated transistor feedback amplifier provides relatively wide bandwidth and relatively large phase and gain margins, irrespective of the transconductance of the transistors in the amplifier. Each one of three preferred embodiments (10, 50, 104) of the invention includes a transconductance stage (20, 68, 68) and an amplifier stage (12 and 14, 54, 54 and 14). The transconductance stage delivers an input signal to the amplifier stage, which produces an amplified replica of the input signal. A feedback capacitor (24, 88, 24 and 88) connected between the output and the input of the amplifier stage provides dominant pole compensation by which the magnitude of the loop gain diminishes by 6 dB/octave with increasing frequency. The capacitor provides a forward feedthrough path for any residual portion of the input signal so that the residual portion arrives at the output of the amplifier stage in substantially the same phase relation with that of the output signal of intermediate frequency.

Abstract: A method and circuit employ digital techniques in processing an input signal of a first frequency to develop an output signal of a second frequency that is a multiple of the first frequency. During each cycle of the input signal, a presettable down counter (146) is decremented from its maximum value at a rate of 1/T.sub.1. The digital word appearing at the output of the down counter at the end of the cycle is programmed into an up counter (278) that is clocked at a rate of 1/T.sub.2. The frequency of the signal developed at the overflow output (336) of the up counter is divided by two by a flip-flop (342) whose output (348) provides a signal of a frequency which is T.sub.1 /2T.sub.2 times that of the input signal. The frequency of the output signal changes after one cycle of a change in frequency of the input signal. The frequency multiplication factor can be a noninteger value.

Abstract: An improved mesh lens for PDA-type cathode-ray tubes is constructed in a manner that permits deformation into a concavo-convex shape with a substantially shorter radius of curvature than heretofore obtainable with prior art devices. A mesh lens (12) formed in accordance with this invention particularly comprises of multitude of interconnected webs (58) forming an array of apertures (60). Each web (58) has opposing ends and a midline (62) extending between those ends. The mesh (12) is configured so that an individual aperture (60) of the array is formed by a set of webs (58) interconnected at their ends. The midline (62) of each web in the undeformed mesh defines a bent line. The mesh can be deformed into a concavo-convex shape having a relatively short radius of curvature. This is so because the individual webs of the mesh respond to the application of deformation forces by initially straightening, thereby effectively delaying the development of tensile stresses in the webs.

Abstract: An electron beam addressed liquid crystal light modulator or "valve" includes a liquid crystal cell having a target surface which a writing electron beam and an erasing electron beam address to provide a display image. The writing electron beam and the erasing electron beam sequentially strike preselected locations on the target surface to cause an emission of secondary electrons and, thereby, develop an electrostatic potential at such preselected locations. A secondary electron collector electrode positioned over and above the target surface collects in a uniform manner the secondary electrons emitted by all regions of the target surface. A collector electrode controller circuit sequentially applies first and second potential differences between the target surface and the collector electrode in synchronism with the striking of the preselected locations by the respective writing and erasing beams.

Abstract: A switchable color filter comprising a pair of twisted nematic liquid crystal devices (126 and 128) and a light polarizing system (108) which includes three color selective polarizing filters (102, 104, and 106) is incorporated as an optical subassembly in a field sequential color display system (100) to provide output states of white light and light of three different colors to form an image in full color and high brightness with strong color contrast.

Abstract: An electrostatic decelerating and scan expansion lens system (10) includes a mesh element (56) and operates in a cathode-ray tube (12) that incorporates a microchannel plate (24). The lens system is positioned downstream of the deflection structure (42 and 44) and provides linear magnification of the electron beam deflection angle. The mesh element is formed in the shape of a convex surface as viewed in the direction of travel of the electron beam (40) to provide a field with equipotential surfaces (100) of decreasing potential in the direction of electron beam travel. Secondary emission electrons generated by the mesh element as it intercepts the electron beam, are therefore, directed back toward the lens system and not toward the microchannel plate. Only the beam electrons strike the microchannel plate, which provides on the phosphorescent display (20) an image of high brightness, free from spurious light patterns.

Abstract: A color image copying system (10) employs a cathode-ray tube (16) that employs a diffraction grating face plate (38) which for each image disperses to predetermined focal regions (132, 143, and 136) light rays of corresponding wavelengths. The light rays sequentially expose a region 80 of a scrolled light-sensitive medium (42) to form a composite color copy of the image. Bands of phosphorescent materials (32, 34, and 36) are applied on angularly inclined subregions (146, 148, and 150) of the inner surface (144) of the face plate and intercept a raster-scanned electron beam (22) to develop light of the different wavelengths. The inner surface of the face plate has angularly inclined subregions (146, 148, and 150) that provide for incident light rays of each wavelength an angular offset of equal magnitude but opposite rotational sense to compensate for changes in diffraction angles (.beta..sub.1, .beta..sub.2, and .beta..sub.

Abstract: An electron beam-addressed liquid crystal cell for a light valve. The cell (40) includes liquid crystal material (42) sandwiched between two substrates (16, 44). One substrate (44) is addressed by the electron beam (60a, 60b) and includes a coating (51) having a rate of secondary electron emission greater than the characteristic rate of secondary electron emissions of the base layer (49) of the substrate (44). The enhanced secondary electron emission characteristics of the coated substrate (44) permit the cell to be modulated with relatively lower electron beam current for correspondingly higher image resolution.

Abstract: A color image copying system (10) includes a light modulator (12) that receives incident light rays emanating from a source (14) of light. The light modulator comprises a light dispersing apparatus (54) that disperses different wavelengths of the incident light rays to different locations on a focal surface (60). A filter mask (68) aligned with the focal surface transmits preselected wavelengths of the ultraviolet light and blocks light of all other wavelengths. Each of a set of light valves (86, 88, 90) receives a different wavelength of light transmitted by the filter mask and intensity modulates it in accordance with image pixel information provided by an information source (16). An optical focusing apparatus (56) focuses the intensity-modulated wavelengths of light to a relatively small location (20) on an image focal surface (22) which is aligned with a light-sensitive medium (24).

Abstract: A combined digital-to-analog converter and latch memory circuit (10) includes an R-2R resistive ladder network (12) and a current-controlled latch memory 18. The R-2R resistive ladder network has plural input nodes (100 and 102) and an analog signal output (104). Each of the input nodes corresponds to a different bit of a digital word that is to be converted to an analog signal. The current-controlled latch memory includes plural subcircuits (14 and 16). Each of the latch subcircuits uses an amount of current to store the logic state of the bit of the digital word and to derive directly the node of the R-2R resistive ladder network. This configuration promotes the efficient use of space, power, and circuit elements.

Abstract: A switchable color filter employs chiral liquid crystal circular polarizers to minimize the attenuation of light passing through a system in which it is incorporated. One preferred embodiment (12) of the switchable color filter includes a light modulator (32) positioned between the light polarizing assembly (20) and first and second chiral liquid crystal cells (36 and 38). The light polarizing assembly receives unpolarized light and transmits circularly polarized light of colors included within first and second narrow color bands. The first chiral cell reflects incident light within the first color band and in a first polarization state, and the second chiral cell reflects incident light within the second color band and in a second polarization state. The light modulator cooperates with a switching circuit (34) to selectively provide first and second polarization switching states.

Abstract: A stereoscopic imaging system employs an image encoder that comprises a variable optical retarder which is positioned face-to-face with an image source and an image decoder that comprises only passive optical elements. In a first embodiment, the imaging system (50) uses a single variable optical retarder (22) to encode perspective view images by selectively developing zero and half-wave retardation. A passive viewing apparatus (52 and 54) employs retardation plates (56, 58, and 64) to decode the images. In a second embodiment, the imaging system (100) uses a pair of variable optical retarders (101 and 102) to encode perspective view images in left- and right-circularly polarized light. A passive viewing apparatus (106 and 108) employs quarter-wave plates (110 and 114) to decode the images. Each of the preferred embodiments is suitable for use with broadband image source phosphors and in processing perspective view images in full color.

Abstract: The present invention provides a parallel or "flash" analog-to-digital converter circuit (A) including a plurality of voltage comparators (20a-20g) arranged in first and second sets (F and E) adapted for receiving separate analog input signals. A push-pull configuration is employed in providing the analog input signal to the comparators of the two sets. The analog inputs (22a-22d) of the comparators (20a-20d) in the first set are provided in input signal V.sub.1 and the analog inputs (22e-22g) of the comparators (20e-20g) in the second set are provided an input signal V.sub.2 of equal magnitude but opposite polarity. Different reference voltages are provided to the reference inputs (24a-24g) of the comparators by a series-connected resistor network (H). Two encoders (I and J) and an adder (K) are used to detect the number of output signals from the comparators in a similar logic state and provide a digital binary output signal corresponding to the number of such outputs.

Abstract: A voltage reference circuit (10) for a constant-current source transistor (16) of the bipolar type provides an output voltage in two components. The first voltage component varies in accordance with the negative temperature coefficient (C.sub.1) of the base (58)-emitter (78) junction of a bipolar transistor (60) to compensate for temperature-related changes in the base (18)-to-emitter (22) voltage of the constant current source transistor. The second voltage component is of fixed magnitude and develops collector current (I.sub.0) flow through the transistor and thereby actuates constant-current source operation. The result is a transistor constant-current source that provides a constant output current independent of temperature.

Abstract: An error correction circuit (16) corrects errors in the thermometer code (T.sub.1 -T.sub.7) developed by a parallel or "flash" analog-to-digital converter (10). The error correction circuit employs plural similar bit exchange modules (34) of which each includes a 2-input OR gate (46) having common inputs (48 and 50) that constitute the inputs of the bit exchange module. The output (52) of the AND gate and the output (54) of the OR gate constitute the outputs of the bit exchange module. The bit exchange modules receive the digital-to-analog converter thermometer code and are interconnected to correct errors therein resulting from the presence of more than one transition between different logic states for adjacent bits in the thermometer code. The error correction circuit manipulates the thermometer code bits to provide a corrected thermometer code (T.sub.1C -T.sub.7C) that has only one transition between different logic states for adjacent bits thereof.