Electronically adjustable positionsensitive radiation detector, focus-error detection system comprising such a radiation detector, and optical read and/or write apparatus comprising such a focus-error detection system

Claim 2

A radiation-sensitive semiconductor device comprising a semiconductor body which provided with at least two subelements on a substantially plane surface, which subelements constitute radiation-sensitive diodes with the adjoining parts of the semiconductor body, the distance between the subelements being small enough to enable the zone of the semiconductor body between the subelements to be depleted completely by the depletion regions associated with the subelements by applying a reverse voltage across the diodes, so as to inhibit charge transfer between the subelements, and a circuit for applying reverse voltage across the radiation-sensitive diodes and for detecting the photoelectric currents generated by the radiation in the radiation-sensitive areas of the diodes constituted by the depletion region, characterized in that the circuit comprises means for applying different reverse voltages across the diodes depending on a control signal, in order to adjust the boundary between the radiation-sensitive areas of the diodes.

Claim 3

A semiconductor device as claimed in Claim 1, characterized in that the circuit comprises at least one differential amplifier, which is fed back and which is intended for converting one of the photoelectric currents generated by the radiation into a measurement signal, for which purpose one of the subelements is coupled to the inverting input of the differential amplifier for applying the current to be converted to said input, the circuit further comprising means for applying a voltage whose amplitude depends on the control signal to the non-inverting input of the differential amplifier.

Claim 4

A semiconductor device as claimed in Claim 2, characterized by a second differential amplifier for generating a measurement signal which is a measure of the difference between the output voltage of the first differential amplifier and the control voltage on the non-inverting input of the first differential amplifier, for which purpose an input of the second differential amplifier is coupled to the output of the first differential amplifier and for which purpose the circuit comprises means for applying a voltage proportional to the control voltage to the other input of the second differential amplifier.

Claim 5

An optoelectronic focus-error detection system for detecting in an optical system a deviation between an element and a plane of focussing of an objective system, in particular for use in an apparatus for reading a record carrier having an optically readable information structure or an apparatus for optically reading information in a record carrier, which focus-error detection system comprises a semiconductor device as claimed in Claim 1, 2, or 3.

Claim 6

An optoelectronic focus-error detecting system for detecting a deviation between a reflective detection surface and a plane of focussing of an objective system for directing a radiation beam towards the detection surface, which detection system comprises a first and a second radiation-sensitive detector each comprising at least two subelements which are arranged substantially parallel to each other on a surface of a semiconductor body and which with the adjoining parts of this semiconductor body constitute two diodes adjoining each other, a beam-splitting element for splitting the radiation beam reflected by the detection surface into a first and a second subbeam which are incident on the first detector and the second detector respectively in the boundary areas of the adjoining diodes of said detectors, a first circuit for applying a reverse voltage across the diodes, and a second circuit for deriving a focus-error signal from the photoelectric currents generated in the diodes by the subbeams is characterized in that the first circuit comprises adjusting means for adjusting the boundaries between the radiation-sensitive areas of the diodes by producing different reverse voltages across the diodes of the first detectors and the diodes of the second detector depending on a control signal, the detection system further comprising a control device for deriving the control signals for the boundary-adjusting means from the photoelectric currents thus generated, in such a way that the sum of the photoelectric current generated in that diode of the first detector which is situated further from the centre between the locations where the beams are incident and the photoelectric current generated in that diode of the second detector which is situated near said centre is maintained substantially equal to the sum of the photoelectric currents generated in the other two diodes.

Claim 7

An optoelectronic focus-error detecting system for detecting a deviation between a reflective detection surface and a plane of focussing of an objective system for directing a radiation beam towards the detection surface, which detection system comprises a first and a second radiation-sensitive detector each comprising at least two subelements which are arranged substantially parallel to each other on a surface of a semiconductor body and which with the adjoining parts of this semiconductor body constitute two diodes adjoining each other, a beam-splitting element for splitting the radiation beam reflected by the detection surface into a first and a second subbeam which are incident on the first detector and the second detector respectively in the boundary areas of the adjoining diodes of said detectors, a first circuit for applying a reverse voltage across the diodes, and a second circuit for deriving a focus-error signal from the photoelectric currents generated in the diodes by the subbeams is characterized in that the first circuit comprises adjusting means for adjusting the boundaries between the radiation-sensitive areas of the diodes by producing different reverse voltages across the diodes of the first detectors and the diodes of the second detector depending on a control signal, the detection system further comprising a control device for deriving the control signals for the boundary-adjusting means from the photoelectric currents thus generated, in such a way that the sum of the photoelectric current generated in that diode of the first detector which is situated further from the centre between the locations where the beams are incident and the photoelectric current generated in that diode of the second detector which is situated near said centre is maintained substantially equal to the sum of the photoelectric currents generated in the other two diodes.

Claim 8

An optoelectronic focus-error detection system for detecting a deviation between a reflective detection surface and a plane of focussing of an objective system for directing a radiation beam towards the detection surface, which detection sytem comprises a radiation-sensitive detector comprising four subelements which are disposed symmetrically relative to a common centre on a surface of a semiconductor body and which together with the adjoining parts of said semiconductor body constitute four adjoining radiation-sensitive diodes, an optical system for directing the radiation beam reflected by the detection surface towards radiation-sensitive diodes of the detector, an astigmatic element being arranged in the optical path between the detection surface and the detector, a first circuit for applying reverse voltages across the diodes, and a second circuit for deriving a focus-error signal from the photoelectric currents generated-in the diodes, is characterized in that the first circuit comprises means for adjusting the boundaries between the radiation-sensitive diodes by producing different reverse voltages across diagonally opposed diodes depending on control signals, said detection system further comprising a control device for deriving the control signals depending on the photoelectric currents generated in the diodes, in such a way that the photoelectric currents generated in diagonally opposed diodes are maintained substantially equal to each other.

Claim 9

An optoelectronic focus-error detection system for detecting a deviation between a reflective detection surface and a plane of focussing of an objective system for directing a radiation beam towards the detection surface, which detection sytem comprises a radiation-sensitive detector comprising four subelements which are disposed symmetrically relative to a common centre on a surface of a semiconductor body and which together with the adjoining parts of said semiconductor body constitute four adjoining radiation-sensitive diodes, an optical system for directing the radiation beam reflected by the detection surface towards radiation-sensitive diodes of the detector, an astigmatic element being arranged in the optical path between the detection surface and the detector, a first circuit for applying reverse voltages across the diodes, and a second circuit for deriving a focus-error signal from the photoelectric currents generated-in the diodes, is characterized in that the first circuit comprises means for adjusting the boundaries between the radiation-sensitive diodes by producing different reverse voltages across diagonally opposed diodes depending on control signals, said detection system further comprising a control device for deriving the control signals depending on the photoelectric currents generated in the diodes, in such a way that the photoelectric currents generated in diagonally opposed diodes are maintained substantially equal to each other.