Abstract: An input circuit in which an input impedance of a reception amplifier connected to a piezoelectric transducer is selected to be lower than an impedance composed of an inter-electrode capacitance of the piezoelectric transducer, an equivalent capacitance of a cable used to connect the piezoelectric transducer to the reception amplifier, etc., that is, the parallel impedance of those elements connected in parallel to the reception amplifier so that the reception amplifier is used as an amplifier of the current detection type.

Abstract: In an optical recording system wherein the intensity of a laser beam is modulated with an input modulation signal so as to record information on a recording medium, the intensity modulation of the laser beam is performed after the pulse waveform of the input modulation signal is converted into two pulses which express the front edge and rear edge of the pulse waveform respectively.

Abstract: An information recording and reproducing apparatus wherein a light beam is applied onto an optical disk having pits previously formed in optical manner thereon. A tracking signal is detected from the light beam which has been modulated by the pits, and information is recorded by applying a record beam modulated by an information signal onto an area between one pit and the succeeding pit while tracking is effected by using the tracking signal.

Abstract: An optical disc device including a semiconductor laser as a light source and making the light output of the semiconductor laser different between an information recording operation and an information reproducing operation is disclosed in which the semiconductor laser is connected in parallel with protection circuit, and in which the protection circuit is put in a short-circuited state between two terminals thereof when a monitor signal corresponding to the light output of the semiconductor laser exceeds a predetermined value.

Abstract: A focal position detecting optical apparatus wherein a light beam focused by a first optical system is irradiated on an object to be illuminated, focal point images are formed at two foci spaced apart from each other by a cylindrical lens disposed in a path of light beam reflected from the object, and a shielding element having a tip edge making an angle of approximately 45.degree. with an operating axis of the cylindrical lens is inserted at a site between the two foci and at which the light beam has a circular cross section to extract a portion of the light beam travelling between the two foci. The extracted portion is detected by two photodetectors disposed symmetrically with an axis lying in substantially the same direction as the tip edge, and the difference between outputs of the two photodetectors is produced for detection of an actual focal position of the first optical system.

Abstract: A method for recording and reproducing information characterized in that an information train in which synchronizing signals are arrayed at equal time intervals between information signals is recorded in an information track on a recording medium which is wobbled in synchronism with the synchronizing signals and at a frequency integral times the frequency of the synchronizing signals, that the information train recorded in the information track is read out by read-out means, and that a position of the read-out means is controlled on the basis of the information train read out. The wobbling waveform is 90.degree. out of phase with a harmonic component of the synchronizing signals.

Abstract: When error detection codes are added to a sampled signal word which is a digital version of audio information and a control signal which is a digital version of system control information to construct a data frame and a control signal frame, respectively, the error detection code for the data frame is generated under an arithmetic condition different from that for the control signal frame. In this manner, frame identification information is superimposed on the error detection codes. In a reproducing unit, the error detection codes containing the identification information are used to check an error in the reproduced sampled signal word and control signal and to effect the discrimination between the data frame and the control signal frame.

Abstract: A differential amplifier circuit wherein one collector of the multicollector of each of first, second and third inverse NPN transistors is connected to a base of the corresponding transistor; the first and second transistors are used as differential input transistors; the other collector of each of the first and second transistors is connected to a PNP transistor serving as a load current source; and an output is derived through the third transistor connected to the second transistor.

Abstract: A comparator circuit comprises first and second transistors having bases for receiving first and second input voltages, respectively, and a third transistor having a base for receiving a third input voltage to be compared with the first and second input voltages. The first, second and third transistors have respective emitters connected in common to a constant current source. Switching means is provided for selectively supplying a potential to the base of the first transistor thereby to turn off the same and is connected to a switch control means, to produce the collector potential of the third transistor or a corresponding potential.