Hitachi, Ltd.

Opnext Japan, Inc.

Yoshinori Nagoya

Ken Takei

Yuji Ishida

Yoshitaka Takasaki

Yasuhiro Kita

Kohei Ishizuka

Takeo Kusama

Takashi Suga

Kouichi Uesaka

Hisaaki Kanai

Osamu Yumoto

Jun'ichi Nakagawa

Takashi Sakai

The provision of a coplanar waveguide coupled with a microstrip line with a transmission line substrate that is used between two functional units of different impedance characteristics allows the input and output impedance matching to be performed, the impedance matching between which coplanar waveguide and microstrip line is performed by the variation of the signal linewidth. It allows the transmission characteristics of the optical transmission device in high frequency band to improve.

Optical modulation device

It is an object of the present invention to reduce the amount of spurious noise generated by an emission line spectrum of a signal propagating around the PLL of a PLL frequency synthesizer carrying out digital-signal processing. In order to achieve the object described above, the present invention provides a PLL frequency synthesizer with the following configuration. In a PLL frequency synthesizer having a charge-pump circuit, a waveform converter is provided at a stage behind the charge-pump circuit. The waveform converter converts the voltage waveform on a time axis of a rectangular wave output by the charge-pump circuit into a waveform which: is symmetrical with respect to a predetermined point of time; oscillates so as to have no direct-current component; and has a maximum value of the absolute values of maximums of wave heights thereof located at the center wherein the absolute value decreases uniformly as the wave height is separated farther away from the center. As a result, the amplitudes of a limited number of emission line spectra forming a spurious signal superposed on a signal propagating around the PLL can be made uniform and a maximum thereof can be held at a low value, allowing the direct-current component to be eliminated from the signal propagating around the PLL.

PLL frequency synthesizer

The present invention designs and implements a high-speed PLL circuit and a high-speed synthesizer using the high-speed PLL circuit which has an increased switching speed, a reduced number of jitters and a reduced magnitude of spurious response. In order to achieve the above, the present invention provides a PLL circuit forming a closed loop wherein: one of the inputs of a phase comparator 1 serves as the input of the PLL circuit and the output of phase comparator 1 is connected to the input of a loop filter 2; the output of loop filter 2 is connected to the input of a voltage-controlled oscillator (VCO) 3; the output of the VCO 3 serves as the output of the PLL circuit; and the output of the VCO 3 is supplied to the other input of phase comparator 1 through a frequency divider 4. The circuit form and circuit constants of loop filter 2 are determined so that the transfer function of the closed loop becomes a Gaussian function.

High-speed phase-locked loop circuit

In an output-controlled power amplifier of a closed loop type, an input signal is inputted to a main path in which the input signal is power-attenuated by a variable attenuator and power-amplified by a power amplifier. A power divider distributes the amplified input signal between the main path and a feedback path diverging from the main path so that the signal distributed to the main path is outputted from the main path to the exterior while the input signal is controlled on the basis of the signal distributed to the feedback path. The feedback path includes a hold circuit for extracting the signal distributed to the feedback path and holding the value of the power of the extracted signal when the power reaches a predetermined value. A control signal for attenuating the power of the input signal inputted to the main path is generated by the hold circuit and is applied through the feedback path to the variable attenuator on the main path to control the power of the input signal. A transfer function of the closed loop has a Gaussian characteristic.

Output-controlled power amplifier, radio communication terminal and

A variable equalizer is provided which, using a single variable resistor, can make compensations in both the directions of the gain side, and the loss side and can set a reference gain as desired. An input signal to be equalized is received as an antiphase input signal of a differential amplifier, an output signal which has been equalized is fed back to the antiphase input signal, and a difference signal between an in-phase input signal and the antiphase input signal is delivered as an output. A resistor is connected between an input terminal and ground, first and second impedance circuits and a variable resistor are connected between an intermediate point of the first-mentioned resistor and ground in the order mentioned, and a voltage at the junction point between the first and second impedance circuits is used as the in-phase input signal.

Variable equalizer

To form a simple and economical variable equalizer, the equalizer is constructed of a differential amplifier having two input terminals to which an input signal to be equalized and an equalized output signal derived from the output terminal are applied, a first impedance circuit connected between the differential amplifier and the output terminal, and a series circuit having a second impedance circuit and a variable resistor connected in series between the output terminal and a ground terminal.

In order to realize a precision variable equalizer of little errors by a simple circuit arrangement, a plurality of variable transmission circuits having variable transfer coefficients are connected in series between input and output terminals, and feed-back and feed-forward are applied from input and output sides of the respective variable transmission circuits to input and output portions of the variable equalizer through transmission networks having specified transfer characteristics.

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Yokohama, Japan

Yoshinori Nagoya