Hitachi, Ltd.

Opnext Japan, Inc.

Akio Osaki

Norio Chujo

Yoshihiko Hayashi

Naohiko Baba

Atsushi Hasegawa

Keiichi Yamamoto

Katsunori Hirano

Takeshi Yamashita

Takayuki Nakao

Tetsuya Aoki

Tomoaki Shimotsu

A sample & hold type phase detector is used in a CDR IC and, in jitter transfer bandwidth adjustment, VCO output waveforms 90&#xb0; out of phase with each other can be inputted to the phase detector, whereby a jitter transfer bandwidth can be calculated by only the measurement of frequency and of a DC voltage and it is possible to make a jitter transfer bandwidth adjustment in DC test for IC.

Optical modules and methods of making the optical modules

A driver circuit comprises a first differential-amplifier circuit having a pair of first transistors with emitters thereof connected to each other and a first resistor provided between an emitter connection point of the first transistors and a first power supply. Different electric potentials are applied to the bases of the pair of the first transistors to set a ratio of a current flowing through one of the pair of the first transistors to a current flowing through the other first transistor at about 1/100 or smaller. An amplitude of an output current is controlled by the higher of the electric potentials applied to the base of one of the first transistors.

Driver circuit and optical-transmission module

A driver circuit comprises a first differential-amplifier circuit having a pair of first transistors with emitters thereof connected to each other and a first resistor provided between an emitter connection point of the first transistors and a first power supply. Different electric potentials are applied to the bases of the pair of the first transistors to set a ratio of a current flowing through one of the pair of the first transistors to a current flowing through the other first transistor at about {fraction (1/100)} or smaller. An amplitude of an output current is controlled by the higher of the electric potentials applied to the base of one of the first transistors.

An amplifier which performs the function of switching on and off its output signal includes an inverted Darlington circuit made up of an input transistor and an output transistor, a first switching circuit connected across the base and the emitter of the output transistor, and a second switching circuit connected between the emitter of the input transistor and the collector of the output transistor. Amplifier also includes means for opening the first switching circuit and closing the second switching circuit to send out an output signal, and for closing the first switching circuit and opening the second switching circuit to stop the output signal. The input and output transistors may be fabricated using vipolar or MOSFET technology because current of a small magnitude flows through the switching circuits, the switching circuits can be formed from elements that are small in size and which have small parasitic capacitance. Consequently, amplifier is capable of operating at high speeds but with low power demands. In addition, amplifier can be miniaturized or formed on a single IC chip.

Amplifier with a function for switching on and off the output signal

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Yokohama, Japan

Akio Osaki