We have developed a GaAs direct-conversion π/4 shifted QPSK modulator IC equipped with variable attenuators for controlling the output power level of the 1.9 GHz Personal Handy Phone system in Japan (PHS). The IC was successfully demonstrated showing state-of-the-art performance with the image rejection ratio of more than 36 dBc at a low input power of -10 dBm in 1.9 GHz frequency range. By using the "Gate Current Control method by Pull-down FET's" (GCCPF), the equipped attenuators vary the output power from 0 dB to -28 dB by 4 dB step. The IC operates at a 2.7 V supply with power dissipation of 259 mW. The 2.64.6 mm2 chip with about 400 elements was fabricated by a 0.5 µm WNx-gate BPLDD GaAs MESFET process.

A miniature transceiver, including highly integrated MMIC front-end, for 1.9 GHz band personal handy phone system(PHS) has been developed. The terminal, adopting direct conversion transmitter and receiver technology, consists of four high-density RF circuit modules and a digital signal processing LSI with 2.7 V power supply. The four functional modules are a power amplifier, a transmitter,a receiver, and a frequency synthesizer. Each functional module includes one IC chip and passive LCR components connected with solder bumps on module substrate. The experimental miniature PHS handset has been fabricated to verify the design concepts of the miniature transceiver. The total volume of the developed PHS terminal is 60cc, including the 12cc front-end which comprises the four RF functional circuit modules. The air interface connection with the PHS base station simulator has been confirmed.