Hitachi, Ltd.

Hitachi Consumer Electronics Co., Ltd.

Miyuki Ikeda

Masanori Ogino

Takeo Yamada

Toshiyuki Kimoto

Tsuneo Fujikura

Takahiko Fujiwara

Yoshihiro Arakawa

Takashi Azuma

Fumio Inoue

Kiyoshi Yamamoto

Kazutaka Naka

Masanori Oguino

Takeshi Katayama

Hideharu Saito

Kunio Umehara

Takashi Itoh

Ichiro Niitsu

Yasuharu Tamuro

Satoshi Ootomo

Tsueno Fujikura

Satoshi Ohtomo

Etsuhiro Nakagiri

Yoshiyuki Imoto

Jiro Kawasaki

Hirotoshi Kemi

A projection display device includes: a dustproof filter that removes dust and a foreign material from drawn air; an air guide path that guides, to a liquid crystal panel, the cooling air blown by a suction fan; an air velocity detector that is arranged in the air guide path and detects the velocity of the cooling air that flows in the air guide path; and a CPU that determines, on the basis of the value detected by the air velocity detector, whether or not the dustproof filter is clogged. The air velocity detector detects the velocity of the cooling air by measuring the temperature of the air in the vicinity of the heat generating element that will be increased due to heat transfer generated by the heat generating element. This configuration improves accuracy in determining whether or not the dustproof filter is clogged.

Projection display device

A CRT display device capable of displaying a signal from the existing image signal source, in which a vertical frequency is approximately fixed and a horizontal frequency is widely distributed beyond a ratio of 3:1, on one image screen. The CRT display device includes a scan converter unit and a display unit. The scan converter unit includes an output horizontal frequency unifying circuit, a horizontal blanking period ratio converting circuit, a vertical frequency converting unit and a vertical blanking period ratio converting circuit. The display unit includes a vertical deflection circuit and a circuit for correcting a vertical S-shaped distortion. In a phase synchronous circuit, a lock-out detector is connected to an output of a three state output digital phase detector, and on the basis of an output thereof, a switch is subjected to the 'ON'/'OFF' control. For a period of time when an output of the lock-out detector indicates a lock-out state, a loop gain of the PLL is increased and the pull-in time is shortened. For the remaining periods of time, i.e., in the steady state, the loop gain is decreased and the noise resistance characteristics are improved.

Scalable CRT display device and phase synchronous circuit for use in

A cathode ray tube display in which a signal for detection of a cathode current is inserted into a part of the vertical blanking period of the video signal to be displayed, a cathode current corresponding to the signal for detection is detected, and a cathode voltage or a grid voltage is negative feedback controlled so that the detected cathode current becomes constant, thereby stabilizing the cathode current. The display has a local overscan circuit for executing a vertical scan on the screen with a width larger than a predetermined scan width only at a timing of the cathode current detecting signal inserted for a vertical blanking period, and even in the case where an underscan system to scan by a width smaller than a predetermined display screen width is used as a scan system of the screen display. The invention prevents a harmful visible display image by the cathode current detecting signal appears on the screen.

Cathode ray tube display

A multi-scan type display apparatus with pointer function includes a multi-scan type display unit for displaying a plurality of kinds of main picture signals having different numbers of scanning lines and a pointer position identifying signal generating circuit for generating a pointer position identifying signal. The pointer position identifying signal generating circuit transfers the pointer position identifying signal to the multi-scan type display unit, the multi-scan type display unit includes a universal vertical position address signal generating circuit, a horizontal position address signal generating circuit, a pointer signal generating circuit and a superimposing circuit. The pointer signal generating circuit generates a pointer signal in response to the pointer position identifying signal, a universal vertical position address signal and a horizontal position address signal, the pointer signal is superimposed on the main picture signal by the superimposing circuit, so that even if the input signal to the multi-scan type display unit is changed over to a different one having a different number of scanning lines, a pointer display position is kept constant on the display unit, and the pointer position can be moved to a desired position by controlling the pointer position identifying signal.

Multi-scan type display system with pointer function

A uniformity correction signal generating apparatus includes a horizontal address signal generating unit and a vertical address signal generating unit for generating address signals (X) and (Y, y) having one-to-one correspondence to a position on a display screen of a display unit, respectively. Upper and lower adjacent lattice point data are read out from an E.sup.2 PROM on the basis of the address signals X and Y. Interpolated correction data are obtained on the basis of the upper and lower lattice point data and vertical lower address coordinates y. The apparatus is suitable for an auto-scan type display unit and can correct the uniformity for gradation and focus by using the inexpensive E.sup.2 PROM without need of a large capacity expensive E.sup.2 PROM.

Uniformity correction signal generating apparatus for display image

An adaptive crosshatch signal generator includes a frequency detector for detecting a horizontal scanning frequency, a square calculator supplied with the detected output of the frequency detector, and a variable pulse width multivibrator controlled to have an output pulse width substantially in inverse proportion to the squared output. Longitudinal lines of a crosshatch signal are formed by the output pulses of the multivibrator. The crosshatch signal has a longitudinal line width which is always substantially equivalent to the distance between adjacent scanning lines and is generated by using a simplified configuration irrespective of input signal format.

Adaptive crosshatch signal generator

A video output circuit of a wide bandwidth comprises a bridged-T-type circuit, a first inductor connected in series to the bridged-T-type circuit, and a shunt circuit connected in series to the bridged-T-type circuit and including a second inductor and a first resistor connected in parallel with each other. The bridged-T-type circuit, the first inductor and the shunt circuit cooperate to constitute together with a plurality of stray capacitors a low-pass filter whose order is at least 4 and whose merit index is at least 3.

Video output circuit with wide bandwidth and low power consumption for

A focus yoke used for an electromagnetically focused CRT display comprises: a cylindrical permanent magnet unit which is disposed around a neck portion of a CRT and is spaced from the circumference of the neck portion; a core unit which defines a toroidal space together with the cylindrical magnet unit for substantially surrounding the neck portion, the core unit forming a magnetic path to guide magnetic lines of force generated by the cylindrical magnet unit; a dynamic focus winding unit disposed in the toroidal space; and a winding unit disposed externally of said toroidal space for eliminating an undesired magnetic field of an inverse polarity generated due to the cylindrical magnet unit.

Focus yoke, electromagnetically focused CRT display with the focus yoke,

Electric charges are stored on a capacitor and then the charges are discharged so that a sawtooth wave for use in a convergence correction circuit for a display or the like is generated. When the sawtooth wave is used for a multi-scan display, the charge period is varied according as the scanning frequency varies, and as a result, a phase error is produced in the parabolic wave obtained by squaring the sawtooth wave. To eliminate the phase error, it is adapted such that the discharging current from the capacitor is passed through a coil and, in addition, the period as the reciprocal of the resonant frequency of the resonance circuit formed of the coil and the capacitor is set to be virtually double the discharge period.

Sawtooth waveform generator for a convergence correction circuit

A digital convergence correction circuit for a CRT display unit deals with the problem of an excessive calculation time of the microprocessor expended for the vertical interpolation by using at least two pieces of ROM (read only memory) devices connected together. The circuit deals with the problem of a step variation of brightness by employment of a novel slope interpolation means which implements interpolation based on a continuous waveform of the first-order differential coefficient at the lattice points of the display screen and a curve interpolation means which forms a more superior convergence system. The circuit uses a blanking means to prevent abnormal states from appearing on the display screen during the transfer period of the digital convergence correction data of a new format at the switching of the scanning format for a video signal to be displayed. The circuit includes a two-dimensional interpolation means which evaluates a set of lattice point data of the new format based on the parameter of the new format from a set of lattice point data of the old format. Consequently, the circuit eliminates the need of having many expensive ROMs for each scanning line and for each format individually, allowing a smaller ROM capacity and a shorter format switching time, and moreover a reduced number of adjustment steps required for individual formats.

Display apparatus based on a digital convergence scheme

A video output circuit for driving a CRT of a grid-cathode differential drive type is disclosed, in which a collector potential of an output transistor in a horizontal blanking interval is detected by a diode arrangement; the potential thus detected is smoothed by a smoothing filtering arrangement output current of the output transistor is controlled by an output obtained by the smoothing filtering arrangement; and negative feedback control is effected so that the collector potential of the output transistor is made constant. In this way, a bias adjusting power supply, which was required heretofore, is made unnecessary.

Video circuit for driving a cathode ray tube

A CRT display including a horizontal deflection circuit. The horizontal deflection coil supplied with a horizontal deflection signal, with inductance L, has an energy-dissipating coil resistance connected in series and hence a second-order distortion expanding the left-hand side of the picture screen of the display and contracting the right-hand side thereof is produced. In the preset invention, to correct for the second-order distortion, the current flowing through the deflection coil means is detected, the deflection distortion component is extracted from the current, and a deflection distortion correcting current corresponding to the deflection distortion is supplied to an auxiliary coil for correcting the horizontal deflection of the electron beam.

Display having automatic correction device for horizontal deflection

In a high prrecision PLL circuit arrangement, a phase detecting circuit produces a detecting signal which is directly proportional to a phase difference between a horizontal synchronizing signal and a voltage-controlled oscillating signal. A loop filter circuit produces a delay signal for delaying a frequency control at a predetermined time constant in response to the detecting signal derived from the phase detecting circuit. A voltage-controlled oscillating circuit produces an oscillating signal having a frequency directly proportional to a voltage of the delay signal from the loop filter circuit. A non-linear circuit includes a non-linear element for changing at least one of an AC gain and a DC gain of the loop filter circuit, and prevents an erroneous capture phenomenon of the PLL circuit arrangement in response to the detecting signal from the phase detecting circuit.

High precision PLL with circuit for preventing erroneous capture

A focus adjusting device for projection display, comprising at least one set of 4-pole magnetic field generating means, and adjustment means for adjusting the magnetic field strength of the 4-pole magnetic field generating means so as to eliminate astigmatism caused by fabrication error and attachment error of an electron gun and a focus coil.

Focus adjusting device for projection display

A vertical deflection circuit for a CRT display device comprises a first negative feedback circuit for detecting a vertical deflection current flowing through a vertical deflection coil feeding it back to a ramp wave generator to thereby stabilize a vertical size of the display image on the CRT screen, second negative feedback circuit connected between the deflection coil to an input of the output circuit for detecting a mean vertical deflection current which is fedback to an output circuit to thereby stabilize a vertical position of the display image on the CRT screen and a controlling circuit for controlling feedback amount of the first and second negative feedback circuits to thereby regulate a vertical size and a vertical position of the display image on the CRT screen variably.

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Yokohama, Japan

Miyuki Ikeda