Sanyo Electric Co., Ltd.

Tottori Sanyo Electric Co., Ltd.

Mitsufumi Yoshimoto

Toshinori Iinuma

Akio Kosaka

Mitsuji Hama

Tsuyoshi Egami

Hama: Mitsuji

A baseband signal generator according to the present invention performs differential encoding and mapping processings for a digital baseband signal and limits bandwidths of the obtained symbol mapping data of an I phase and a Q phase by digital filters. Each digital filter includes a circuit for accumulating symbol mapping data corresponding to a plurality of symbol sections, a plurality of ROMs provided corresponding to the plurality of symbol sections for storing symbol data corresponding to a predetermined filter waveform, and an adder for adding symbol data output from there ROMs. The adder outputs a digital baseband signal whose bandwidth is limited, which signal is converted into an analog baseband signal by a D/A converter and supplied to an analog modulation unit.

Baseband signal generator for digital modulator

A digital DQPSK modulator according to the present: invention limits respective bands of symbol mapping data of I phase and Q phase obtained by applying differential encoding and mapping processings to a digital baseband signal, and multiplies the obtained data by the carrier signals by means of the digital filter. Such limiting of the bands and multiplication by the carrier signals are carried out by the digital filter in a time-divisionally multiplexed manner. The digital filter includes a circuit, for accumulating symbol mapping data for each of the I phase and the Q phase corresponding to a plurality of symbol sections, a plurality of ROMs corresponding to the plurality of symbol sections for storing a multiplication result of symbol data corresponding to a predetermined filter waveform and the carrier signal, and an adder for adding data output from these ROMs. The adder outputs a digital modulated signal which is, in turn, converted into an analog modulated signal by a D/A converter.

Digital DQPSK modulator

A digital modulator includes a signal source for a digital baseband signal and a signal source for carrier phase information. The digital baseband signal is converted into amplitude information of an I phase, a Q phase, an I' phase and a Q' phase by a mapping circuit. The carrier phase information is converted into four phase information with phases shifted by shift registers to be out of phase by .pi./4 from each other. The digital modulator includes four ROM, each ROM outputting a multiplication result of the corresponding amplitude information and carrier signal based on the corresponding one of the four amplitude information as a higher order address and the corresponding one of the four phase information as a lower order address. These outputs are added to each other in a digital manner and then converted into an analog signal which is supplied as a modulated signal.

Digital modulator and baseband signal generator for digital modulator

A circuit for use in reproducing a PCM signal recorded on a recording medium in a normal mode and a special mode, to control the frequency of a reproduction clock in accordance with variations in the frequency of the PCM signal. The speed of the medium and the speed of the head, or the frequency of a single-frequency signal in a track format recorded on the signal recording track of the medium is detected to produce a band control signal in accordance with the PCM signal frequency to shift the operating band of a voltage-controlled oscillator in the circuit.

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Nara, Japan

Mitsufumi Yoshimoto