A power amplifier employing a novel linearizing technique is proposed and is applied to digital mobile communication systems. The amplifier offers both high efficiency and excellent adjacent-channel power leakage (ACP) characteristics. The power added efficiency (PAE) of the proposed amplifier is 51% with an ACP of 45 dBc, which is the PDC standard (one of the Japanese mobile communication systems standards). This amplifier can be applied to various systems merely by changing the ROM data.

A novel sampling comparator circuit is presented for extending the pull-in range of microwave phase-locked oscillators (PLOs). It performs both phase and frequency detection without any frequency dividers, and a GaAs MMIC prototype is developed and tested. The proposed comparator improves the pull-in range by about 10 times more than is possible with conventional sampling phase detectors.

A Simple decoding method for short-range MIMO (SR-MIMO) transmission can reduce the power consumption for MIMO decoding, but the distance between the transceivers requires millimeter-order accuracy in order to satisfy the required transmission quality. In this paper, we propose a phase difference control method between each propagation channel to alleviate the requirements for the transmission distance accuracy. In the proposed method, the phase difference between each propagation channel is controlled by changing the transmission (or received) power ratio of each element of sub-array antennas. In millimeter-wave broadband transmission simulation, we clarified that when sub-array antenna spacing is set to 6.6 mm and element spacing of sub-array antenna is set to 2.48mm, the proposed method can extend the transmission distance range satisfying the required transmission quality, which is that bit error rate (BER) before error correction is less than 10-2 from 9∼29mm to 0∼50mm in QPSK, from 15∼19mm to 0∼30mm in 16QAM, and from only 15mm to 4∼22mm in 64QAM.

A method for increasing alignment tolerance in simple multiple-stream transmission is described. Its use of π-shifted antenna directivity phase enables it to cancel interference even when antenna placement deviations occur. The interference cancellation by using π-shifted directivities provides higher alignment tolerance than that with conventional fixed weight methods. It also provides smaller channel gain variation than can be obtained using fixed weights even when antenna displacement occurs. An objective function is described that is determined by the alignment tolerance. The function is defined to maximize the alignment tolerance. The method's validity is confirmed by an experimental analysis of two-stream transmission in which the alignment tolerance of the proposed method is compared to that of conventional fixed weight methods.

A broadband RF front-end having a direct conversion architecture has been developed. The RF front-end consists of two broadband quadrature mixers, a multi-band local oscillator, and a broadband low-noise variable gain amplifier (LNVGA). The mixer achieves broadband characteristics through the incorporation of an in-phase power divider and a 45-degree power divider. The in-phase power divider achieves broadband characteristics through the addition of a compensation capacitor. The 45-degree power divider achieves broadband phase characteristics through the addition of a compensation capacitor and a compensation resistor. The local oscillator, which is composed of two VCOs, two frequency dividers, and four switches, can cover three systems including one FDD system. The LNVGA achieves its broadband characteristics without the use of reactance elements, such as inductors or capacitors. In a trial demonstration, when the RF frequency was between 900 MHz and 2.5 GHz, the mixer for a demodulator experimentally demonstrated an amplitude balance of less than 1.6 dB and a quadrature phase error of less than 3 degrees. When the RF frequency was between 900 MHz and 2.5 GHz, the mixer for a modulator demonstrated an image ratio of less than -30 dBc. The local oscillator demonstrated multi-band characteristics, which are able to cover the target frequencies for three systems (PDC, PHS, 2.4 GHz WLAN). From 900 MHz to 2.5 GHz, the amplifier shows a noise figure of less than 2.1 dB and a gain of 28 1.6 dB.