Nippon Hoso' Kyokai

Japan Radio Co., Ltd.

Michitoshi Minami

Yutaka Kojima

Kazuhisa Hayeiwa

Hisashi Naka

An amplitude modulation circuit and method. A predetermined number of (e.g., 6) drivers and differentially switched power amplifiers are provided in pairs. A program sound signal which has been quantized into a predetermined number of bits (e.g., 12 bits) is divided through a ROM into a plurality of bit groups each consisting of a predetermined number of bits (e.g., 2 bits), which are in turn distributed to the respective driver and differentially switched power amplifier pairs. In response to the value of the distributed bit group, each driver selects two different phase-shift carriers from seven different phase-shift carriers, and provides as its outputs .phi..sub.A and .phi..sub.B. With the output phase-shift carriers (.phi..sub.A and .phi..sub.B), each driver differentially switches the differentially switched power amplifier corresponding thereto. The output of each differentially switched power amplifier is weighted. The outputs of all the differentially switched power amplifiers are combined by a power combiner and then filtered through a BPF, thereby obtaining a broadcast output which has been amplitude modulated by the program sound. Thus, a digital amplitude modulation can be realized using a lower number of power amplifiers than before.

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Mitaka, Japan

Michitoshi Minami