Oki Electric Industry Co., Ltd.

Kazuo Suto

Hiroyuki Yamada

Hidehisa Murayama

A modulator according to the invention includes: a PLL circuit that detects a phase difference between an input signal and a reference signal, an AGC circuit that controls a gain of a modulating signal and outputs a control signal, and a voltage controlled oscillation circuit that controls an oscillation frequency of a signal outputted from the PLL circuit on the basis of the control signal. Here, the voltage controlled oscillation circuit includes: a first voltage controlled reactance unit that inputs the signal outputted from the PLL circuit, a second voltage controlled reactance unit that inputs the control signal, and a high-frequency oscillation circuit connected in parallel with the first and second voltage controlled reactance units, which outputs the input signal. Thereby, the invention achieves to provide a modulator capable of compensating the deviation of the modulation factor, even when the frequency of the carrier signal varies.

Modulator

A signal deciding apparatus which can obtain a stable digital signal OUT irrespective of an amplitude and a duty ratio of an input signal IN is provided. The input signal IN is amplified by inverters ( to and ) and outputted as a digital signal OUT. A signal (S ) on the input side of the inverter ( ) is integrated by a time constant which is equal to a data period of the input signal IN by an integrator ( ) and supplied to a differential amplifier ( ). A signal (S ) on the output side of the inverter ( ) is integrated by a large time constant by an integrator ( ), a control voltage VC supplied from a control terminal ( ) is multiplexed to the integrated signal S and a resultant signal is sent to the differential amplifier ( ). An output signal of the differential amplifier ( ) is integrated by a resistor ( ) and a capacitor ( ) and its average level is fed back as a threshold voltage to the input side of the inverter ( ) through a resistor ( ) and multiplexed to the input signal IN. Thus, the digital signal OUT based on the duty ratio of the input signal IN is obtained.

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Tokyo, Japan

Kazuo Suto