Abstract: A photo detective unit includes a photo detective semiconductor chip including a photo detective element formed under a first manufacturing condition and a buffer circuit for shaping output waveform of the photo detective element, and a signal processing semiconductor chip formed under a second manufacturing condition and responsive to voltage from the photo detective semiconductor chip for generating digital data, and the photo detective semiconductor chip and the signal processing semiconductor chip are together accommodated in a single package.

Abstract: A photo detective unit includes a photo detective semiconductor chip including a photo detective element formed under a first manufacturing condition and a buffer circuit for shaping output waveform of the photo detective element, and a signal processing semiconductor chip formed under a second manufacturing condition and responsive to voltage from the photo detective semiconductor chip for generating digital data, and the photo detective semiconductor chip and the signal processing semiconductor chip are together accommodated in a single package.

Abstract: Light is made incident on a pair of photo-sensors having different sensitivity characteristics. One of them has higher spectroscopic sensitivity than the other within a specified range of wavelength, but the other has spectroscopic sensitivity over a wider range of wavelength than this specified range. Both of the photo-sensors are adjusted so as to have approximately same photo-sensitivity against external background light. A difference current with intensity equal to the difference between the currents generated by this pair of photo-sensors is obtained by a subtraction circuit and is compressed by a compression circuit by a specified ratio, and the compressed current thus obtained is outputted.

Abstract: A light receiving portion which receives light from a light emitting portion through slits formed in a rotating disc is provided with, first, second and third photodiodes. With an output of the second photodiode as a reference value, an output of the first photodiode is compared with the reference value and pulsed by a first comparator, and an output of the third photodiode is compared with the reference value and pulsed by a second comparator. With such a light receiving apparatus, since the output (reference value) of the second photodiode similarly decreases when the outputs of the first and third photodiodes decrease due to a decrease of the light quantity of the light emitting portion, the deviation of the phase difference never occurs between outputs of the first and second comparators.