Hitachi, Ltd.

Hitachi Communication Technologies, Ltd.

Yoshinobu Morita

Yusuke Yajima

Tohru Kazawa

Masaki Ohira

Akihiko Tsuchiya

Hiroki Ikeda

Daisuke Mashimo

In a gain-switching-type transimpedance amplifier, in order to provide a technique capable of preventing unnecessary gain switching caused when noise is received, and preventing decrease in sensitivity caused when noise with a large input level is received, and then, a burst signal with a small input level is received, a transimpedance amplifierincludes: a pre-amplifierto which the burst signal is inputted; an average detection start determination unitfor comparing an output of a pre-amplifierwith a first threshold voltage; an average detection circuitfor detecting and outputting an average value of the output of the pre-amplifierduring a certain period of time from a time point when the output of the pre-amplifierexceeds the first threshold voltage; and a gain switching control unitfor determining whether to switch a gain of the pre-amplifierbased on an output of the average detection circuit

Transimpedance amplifier and PON system

In a light reception element such as an APD (Avalanche Photo Diode) used for receiving a high-speed and weak optical signal, it is possible to prevent the phenomenon of distortion of a signal inputted after a large-level light is received. A PON (Passive Optical Network) system includes an OLT (Optical Line Terminal) which can impartially and effectively transmit light reception data to each ONU (Optical Network Unit). According to a light reception amplitude received by each ONU, an inter-frame gap of an appropriate length is assigned for each ONU. The OLT includes a unit for measuring and accumulating the reception light amplitude and data on the inter-frame gap of an appropriate length decided in advance according to the characteristic of the light reception device and generates a grant value for assuring an inter-frame gap of an appropriate length by using the both information.

Apparatus of adjusting optical signal transmission timing

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Yokohama, Japan

Yoshinobu Morita