Fujitsu Corporation

Tadao Ogawa

Kazuo Yamaguchi

Nobuhide Yamaguchi

Yukou Mochida

A low noise amplifier, comprising a grounded emitter transistor amplifier having a parallel impedance element connected between base and collector and a series impedance element connected between emitter and ground. The parallel impedance element is selected to have a pole near a zero of the series impedance element, and the parallel impedance element also has a zero near a pole of the series impedance element. The impedances of the series impedance element and of the parallel impedance element vary oppositely with respect to frequency, so that the input impedance of the amplifier is constant with respect to frequency. However, by selection of two impedances which are thus matched, the gain is increased at high frequencies and slightly reduced at low frequencies. Thus, the total noise figure is improved, due to the higher gain at the higher frequency range. In addition, frequency-selective attenuation imposed by a transmission line is compensated for, so that the amplifier has increased immunity to low-frequency overload.

Low noise amplifier circuit with reduced low-frequency gain

An optical fiber communication system using group transmission which transmits PCM information by utilizing an optical fiber group composed of a plurality of optical fibers. The PCM information in a plurality of optical fibers is stored in a memory of the system's sending terminal, the stored information of each memory is read out by simultaneous clock pulses so as to send out the information to a transmission line which is composed of a plurality of said optical fibers. A repeater is provided in the transmission line having at least one of the following circuits, an AGC circuit, a light element control circuit, a power supply circuit and a supervisory circuit. The supervisory circuit is commonly provided for checking a plurality of signals which is transmitted by the above-mentioned optical fibers. In the repeater, the signals are regenerated by simultaneous clock pulses which are generated from one common timing circuit, and the phases of the signals are arranged in order for sending out said signals to the transmission line composed of said optical fibers.

Growing community of inventors

Kawasaki, Japan

Tadao Ogawa