Abstract: A laser diode light emission sensing circuit comprises a photodiode 3 which senses a lightwave signal of a laser diode to convert it into a current signal, an I/V converting circuit 4 which converts the current signal from the photodiode 3 into a voltage signal, a comparator 6 which compares the voltage signal from the I/V converting circuit 4 with a reference voltage of a reference voltage source 5 to output a prescribed signal when the voltage signal from the I/V converting circuit 4 exceeds the reference voltage from the reference voltage source 5, the reference voltage source 5 which outputs the reference voltage to comparator 6, an inverter 9 which inverts an output of a CELL signal, and DFF circuit 7 which utilizes the output of the comparator 6 as a clock input, while utilizes an output of the inverter 9 as a reset input, and maintains always the data input at a high level, whereby a luminous state of the laser diode can be maintained digitally.

Abstract: An automatic threshold level control circuit is provided which is capable of controlling the threshold level without causing the DUTY deterioration. The automatic threshold level control circuit comprises a timing detecting circuit 110a, used for preserving the peak voltage values of each input signals for input signals (ATCIN+ and ATCIN−) and for outputting the preserved voltage values as a reference signal for the threshold level of each input signal, and the automatic threshold level control circuit comprises a pair of peak value detecting circuits PD1 (62) and PD2 (64) for resetting the held voltage values into reference voltages Vref1 and Vref2 by reset signals PD1RST and PD1RST; and the timing detecting circuit 110a for detecting a predetermined timing and outputting the reset signals PD1RST and PD2RST to the peak value detecting circuits PD1 and PD2 for releasing the reset state in accordance with the detected timing.

Abstract: A transimpedance-type amplifier circuit includes a first resistor connected to a switching device and a second resistor connected with the first resistor in parallel with the switching device which is turned on in accordance with a result obtained by comparing an output from an inverting amplifier with a reference voltage. A diode is connected in parallel with the first resistor which is connected to the switching device, altering a feedback resistance constituted of these components. The diode maintains a terminal voltage across the first resistor to constant, and an optical current signal from a photodiode is therefore passed to discharge an electric charge accumulated in the parasitic capacitance of the photodiode.

Abstract: In order to effectively amplify an electrical signal converted from an optical signal, first and second amplifiers are coupled in series. A controller is arranged such as to receive outputs of the first and second amplifiers and to produce first and second control signals based on the outputs. The first and second amplifiers respectively change gains thereof in response to the first and second control signals. The output of the second amplifier is an output of the arrangement.

Abstract: A diode for passing the output of a differential amplifier to a holding capacitor is short-circuited in response to a first switching signal, thereby causing the holding capacitor to be discharged through the short-circuiting circuit under control of a second switching signal. The first and second switching signals are generated by delaying a reset signal. The first switching signal is terminated before the termination of the second switching signal.