Optical transducer and recording/playback device comprising the transducer

#The invention relates to an optical transducer comprising optical detection means including a first, a second, a third and a fourth optical detector, such that a first imaginary line from the third optical detector to the first optical detector crosses a second imaginary line from the second optical detector to the fourth optical detector which optical detectors generate detection signals in response to an intensity of radiation incident thereon, the optical transducer further comprising signal combination means for generating a combination signal which is indicative for a sum of electrical detection signals.

#The invention further relates to a recording/playback device comprising the transducer.

#A transducer as described in the opening paragraph is used in commercially available CD-players. In the known transducer, the combination means generate a combination signal which is indicative for the sum of the detection signals of the first, the second, the third and the fourth detector. This signal as well as four signals indicative for the detection signals of each of the detectors are provided via a flexible cable to a signal processing unit. The combination signal serves as an input signal for a data retrieval unit comprising bit detection means, channel decoding means and error correction decoding means. The four signals indicative for the detection signals are used to calculate a DPD tracking signal.

#FIG. 1 shows an embodiment of an optical transducer according to the invention,

#FIG. 2 shows a in more detail a portion of the embodiment of FIG. 1,

#FIG. 3 shows an overview of a plurality of operational modes of the optical transducer,

#FIG. 1 shows an embodiment of an optical transducer according to the invention. The optical transducer comprising optical detection means 1 including a first 1A and a second optical detector 1B next to each other on a first side of an imaginary line 2 which extends in a first direction 3. The detection means 1 further include a third 1C and a fourth optical detector 1D on the other side of the line 2. The third optical detector 1C is arranged next to the second optical detector 1B and the fourth optical detector 1D is arranged next to the first optical detector 1A. A first imaginary line 2a from the first 1A to the third detector 1C crosses a second imaginary line 2b from the second 1B to the fourth detector 1D. The optical detectors 1A, . . . , 1D generate detection signals A, . . . ,D in response to an intensity of light incident thereon. The detection signals A, B, C, D are pre-amplified by variable gain amplifiers 8. The optical transducer further comprises signal combination means 4 and further signal combinations means 5, still further signal combination means 6 and signal selection means 7.

#An implementation of the embodiment of FIG. 1 is described in more detail with reference to FIG. 2. The optical transducer comprises the combination means 4 for generating a combination signal AC+ which is indicative for the sum of the electrical detection signals A,C of the first 1A and the third optical detector 1C. The optical transducer also comprises the signal combination means 4 for generating a first AC−, a second BD+ and a third additional combination signal BD+. The first additional combination signal AC− is also indicative for the sum of the electrical detection signals A,C of the first 1A and the third optical detector 1C. The first additional combination signal AC− and the combination signal AC have a mutually opposite phase. The second BD+ and the third additional combination signal BD− each are indicative for the sum of the electrical detection signals B, D of the second 1B and the fourth optical detector 1D. The second BD+ and the third additional combination signal BD− have a mutually opposite phase.

#As shown in FIG. 2, the signal combination means 4 include a first addition element 41 for generating a first intermediary signal AC and a second addition element 42 for generating a second intermediary signal BD. The signal combination means 4 further include a third addition element 43 for generating the combination signal AC+ from the first intermediary signal AC and a reference value VR. The signal combination means 4 also include a first subtraction element 44 for generating the combination signal AC− from the first intermediary signal AC and the reference value VR. The signal combination means 4 further include a fourth addition element 44 for generating the combination signal BD+ from the second intermediary signal BD and the reference value VR. The signal combination means 4 also include a second subtraction element 44 for generating the combination signal BD− from the second intermediary signal BD and the reference value VR. Different implementations of the signal combination means 4 are possible. E.g. instead of first adding the signals A and C and subsequently the reference value VR, the signal AC+ could also be obtained by interchanging these additions, or by performing the additions by one addition element.