Makoto Kawashima

A new tunable filter using love wave resonators for reconfigurable RF

A large number of frequency bands have been included in mobile phone handsets and in their RF front end circuit, RF paths have been increasing and the configuration has been becoming complex more and more. A new tunable filter is proposed in this paper. In order to realize a wide bandwidth SAW resonator using extension inductor, Love wave SAW resonator for the tunable filter can be obtained by the optimization of the Euler angle and Pt film thickness to avoid Rayleigh wave spurious and the bulk wave. A tunable filter is fabricated for the operation in the low frequency band of 669-960MHz which fractional bandwidth is 31.5%. This result shows promising possibility of a tunable filter for reconfigurable RF.

A new tunable RF front-end circuit for advanced 4G handsets

A large number of frequency bands have been included in mobile phone handsets and in their RF front end circuit, RF paths have been increasing and the configuration has been becoming a complex more and more. A new tunable RF front-end circuit for single RF chain architecture is proposed in this paper. A tunable duplexer composed of wideband circulator and SAW based tunable filters for TX and RX, and a tunable low RX noise power amplifier have been developed. RX band noise level in FDD system is studied. Those devices are fabricated for the operation in the low frequency band of 669-960MHz which fractional bandwidth is 31.5%. Experimental results in Band 5 and Band13 show 40dB isolation of the tunable duplexer and 10dB noise level improvement of the tunable low RX noise PA, which achieve target value of 50dB suppression of RX band noise. This results show promising possibility of simple RF front-end of future mobile handsets.

A miniaturized broadband lumped element circulator for reconfigurable front-end system

A novel miniaturized broadband circulator for reconfigurable mobile handsets has been successfully developed. The circulator operating in a weak magnetic field below ferromagnetic resonance is derived by analyzing the equivalent circuit. The operating theory of the circulator has been confirmed by using the perturbation theory. The usable isolation band could be expanded to 1.71GHz to 2.17GHz, which is a very small sized 1.2 × 1.0 × H0.5 mm3 such as 1/25 compared with the conventional one, Core-Circulator is realized. The developed circulator keeps characteristics as the insertion loss of 1.1dB maximum and the TX-RX isolation of 21dB minimum which have achieved the requirements of the tunable RF front-end.

A new tunable SAW filter circuit for reconfigurable RF

In recent years, the mobile data traffic is increasing and many more frequency bands have been employed in cellular handsets. A simple π type tunable band elimination filter (BEF) with switching function has been developed using a wideband tunable surface acoustic wave (SAW) resonator circuit. The frequency of BEF is tuned approximately 31% by variable capacitors without spurious. In LTE low band, the arrangement of TX and RX frequencies is to be reversed in Band 13, 14 and 20 compared with the other bands. The steep edge slopes of the developed filter can be exchanged according to the resonance condition and switching. With combining the TX and RX tunable BEFs and the small sized broadband circulator, a new tunable duplexer has been fabricated, and its TX-RX isolation is proved to be more than 50dB in LTE low band operations.

New compact Doherty power amplifier design for handset applications

In this paper, new compact Doherty power amplifier design for handset applications, which requires only two components for output network, is proposed. Based on simplified output network, the proposed Doherty power amplifier is analyzed. The proposed Doherty power amplifier is demonstrated experimentally with InGaP-HBT at 2.5 GHz. A PAE of 41.3% and an E-UTRA ACLR of −36.3 dBc at an average output power of 27.7 dBm are measured under LTE 10 MHz, QPSK, 12 RB operation, and the efficiency improvement from Class AB operation achieves 11%.

Novel broadband Doherty power amplifier design for multiband handset applications

In this paper, novel broadband Doherty power amplifier design for multiband handset applications, which requires only two components for output network, is proposed. Based on simplified output network, the proposed Doherty power amplifier is analyzed. The proposed Doherty power amplifier is demonstrated experimentally with InGaP-HBT. A PAE of 45.3% and an E-UTRA ACLR of −36.1 dBc at an average output power of 27.5 dBm are measured at 800 MHz under LTE 10 MHz, QPSK, 12 RB operation, and the efficiency improvement from Class AB operation achieves 12%. Moreover, the proposed Doherty power amplifier maintains more than 41.2% efficiency with an E-UTRA ACLR of below −35.5 dBc from 700 MHz to 950 MHz, corresponding to 30% fractional bandwidth.

A novel switchable SAW Duplexer for band 28

Band 28 has wide bandwidth of 45MHz and narrow duplex gap of 10MHz in 700MHz band, and since digital terrestrial TV channels in some countries are overlapped with lower frequency range of the uplink band, two types of duplexer which have slightly shifted passbands need to be used. This paper describes a novel switchable SAW duplexer which can cover both bands in one duplexer. By using a filter design technique with unique switching circuit, and wideband and low temperature drift SAW resonator technology, high performance such as 2.6/3.0dB insertion loss and 55dB isolation have been achieved, in addition to more than 13/16dB near point attenuation only 5/8MHz apart from the passband edge. The developed switchable duplexer can lead the reduction of 40% in mounting area on RF front-end circuit of mobile terminals.

A study on low Rx-band noise power amplifier for reconfigurable RF front-end circuit

RF paths in mobile phone have been increasing and the configuration has been becoming a complex year by year. A new tunable RF front-end circuit for a single RF chain architecture was proposed. That solution needs the tunable low RX-band noise power amplifier(LNPA) in order to reduce the noise at a RX input port of a transceiver IC in cooperation with the tunable duplexer in FDD system handsets. In this paper, a principle of LNPA is described and it is shown that an interstage filter is effective compared with other circuit configulations. The required characteristics for the interstage filter in LNPA are studied and the RX band attenuation of the interstage filter is calculated with employing equations using noise figure and gain parametaers. It is found that the RX-band noise floor of LNPA is determined by the noise level of a back stage amplifirer Q2, when the interstage filter RX band attenuation is more than 25dB. LNPA is fabricated to clarify the operation and less than -140dBm/Hz which is the target value of the system can be obtained. This results show the promising possibility of Tunable LNPA for simple RF front-end for future mobile handsets.

A novel 4-port lumped element circulator for high-isolation duplex architecture

A novel 4-port circulator for multi-standard and multi-band cellular handsets has been successfully developed by using the Core-Circulator technique. The circulator is realized with lumped element circuits and a weak magnetic field operation. The insertion loss of 1.3dB maximum in 777-787MHz (Band 13) and the TX-RX isolation of 20dB minimum in 35% fractional bandwidth which is including cellular whole low-band have been obtained. Its size is 2.0 mm width X 2.0 mm length X 0.5 mm height. Experimental results of the combination of conventional SAW filters and the developed 4-port circulator have exhibited an extremely high isolation performance of 79dB and robustness against variations of antenna impedance.