Abstract: Provided is an optical receiving device which can achieve a wide dynamic range while keeping a constant extinction ratio against the changes in the input amplitude. A signal current of a light receiving element is converted to a signal voltage by an amplifier and the gain of the amplifier is regulated by a transistor. A DC voltage corresponding to the peak value of the signal current detected by a current detection circuit is outputted to a dummy current generating circuit. The resistance value of the transistor is controlled by a control voltage, which is outputted from an amplitude control circuit according to the difference between the DC voltage and a reference voltage, thereby to set the amplitude of the signal voltage converted by the amplifier to be invariable.

Abstract: Provided is an optical receiving device which can achieve a wide dynamic range while keeping a constant extinction ratio against the changes in the input amplitude. A signal current of a light receiving element is converted to a signal voltage by an amplifier and the gain of the amplifier is regulated by a transistor. A DC voltage corresponding to the peak value of the signal current detected by a current detection circuit is outputted to a dummy current generating circuit. The resistance value of the transistor is controlled by a control voltage, which is outputted from an amplitude control circuit according to the difference between the DC voltage and a reference voltage, thereby to set the amplitude of the signal voltage converted by the amplifier to be invariable.

Abstract: A first stage amplifier circuit includes an amplifier, a variable feedback resistance, a comparator and a shift register. The amplifier amplifies an input signal supplied thereto. The variable feedback resistance includes two or more feedback resistors and one or more switches for changing the connection of the feedback resistors and thereby changing the composite resistance of the feedback resistors. The variable feedback resistance is connected between the output terminal and the input terminal of the amplifier. The comparator judges whether or not the output signal of the amplifier exceeds a predetermined threshold value. The shift register has one or more stages corresponding to the switches of the variable feedback resistance. The shift register operates the switches of the variable feedback resistance one by one and successively reduces the composite resistance of the variable feedback resistance as long as the output signal of the amplifier is judged by the comparator to exceed the threshold value.

Abstract: A laser-diode driving circuit that ensures that the optical output of a laser diode will be stable within a wide temperature range. This circuit includes a reference voltage generator for generating a reference voltage, a control voltage generator for generating a control voltage, an amplifier for producing an amplified output signal corresponding to the difference between the reference voltage and the control voltage, and a driving current generator for generating a driving or operating current for driving a laser diode. The driving current generator is driven by the amplified output signal. The control voltage has a temperature dependence approximately the same as that required for keeping an optical output of the laser diode at a specified level independent of the ambient temperature change.