Fujitsu Corporation

Shinichiro Sano

Kenichi Kobayashi

Makoto Miyoshi

Setsuo Misaizu

Norio Nagase

Yasuhiro Tanaka

Hiroo Kitasagami

Tomoyuki Otsuka

Akihiko Hayashi

Kakuji Inoue

Masahiko Yamashita

Hirokazu Osada

Kazuhisa Kogure

Tatsuya Nishimura

Takayoshi Ikegami

The invention relates to a modulation controlling circuit for supplying a modulating signal to an external modulator that outputs a modulated optical signal, while setting a proper operating point in the external modulator. The external modulator that operates in cooperation with the modulation controlling circuit of the invention enables high-quality modulation at a wide bit rate range. Therefore, in an optical transmission system or a measuring instrument to which the invention is applied, the characteristics and the performance are improved and the operation is made stable without loss of advantages of the external modulator.

Modulation controlling circuit

In an equalizing amplifier that equalizes an electric signal obtained from a light signal received via an optical transmission path, an AGC circuit generates first and second signals from the electric signal by referring to a threshold voltage. The first and second signals are complementary signals. An offset compensation circuit generates a first difference signal based on a difference between the first and second signals, compares the first difference signal with a first reference signal, and outputs, as the threshold voltage, a resultant error signal to the AGC circuit. The threshold voltage is varied so that it is located in the center of an amplitude of the electric signal whereby an offset of the AGC circuit can be compensated for.

Equalizing amplifier, receiver using the same and preamplifier

Growing community of inventors

Yokohama, Japan

Shinichiro Sano