PREAMPLIFIER, OPTICAL RECEIVER, OPTICAL TERMINATION DEVICE, AND OPTICAL COMMUNICATION SYSTEM

摘要

A current bypass circuit that passes part of a photocurrent output from a photodetector is connected to an input terminal of a current-to-voltage conversion amplifier circuit. A voltage obtained by level conversion of an output voltage by a voltage level conversion circuit is input into the current bypass circuit so that the current bypass circuit is turned on at a photocurrent that is smaller than the photocurrent at which a diode connected in parallel to a feedback resistor of the current-to-voltage conversion amplifier circuit is turned on. Consequently, the current-to-voltage conversion gain is switched in three stages according to the intensity of the photocurrent corresponding to an optical signal level.

主权项

1. A preamplifier comprising:
a current-to-voltage conversion amplifier circuit that converts all or part of a signal current into a signal voltage, and amplifies and outputs the signal voltage; a gain varying portion that varies a conversion gain of the current-to-voltage conversion amplifier circuit so that the conversion gain has a point of variation when an input current is equal to a first threshold value; a current bypass circuit that bypasses part of the signal current according to the intensity of the signal current; and a voltage level conversion circuit that outputs to the current bypass circuit a level-converted voltage obtained by level conversion of the signal voltage at a predetermined ratio; wherein a second threshold value that is the intensity of the input current of the current-to-voltage conversion amplifier circuit when the level-converted voltage output from the voltage level conversion circuit becomes a voltage of a threshold value for switching between whether or not to execute a bypass of the current bypass circuit, is less than the first threshold value.