Yorito Ota

Source second-harmonic control for high efficiency power amplifiers

A novel technology that drastically improves output power and efficiency of amplifiers has been developed, where source and load second-harmonic impedances, as well as the fundamental impedances, are optimally terminated in the input and output matching circuits. A record high 74% power-added efficiency (PAE) with 31.4 dBm (1.4 W) output power at a frequency of 930 MHz has been achieved as a single-stage saturated amplifier using an ion-implanted GaAs MESFET under the low supply voltage of 3.5 V. As a single-stage linear amplifier, an excellent PAE of 59% with 31.5 dBm output power has been realized at V/sub d/=4.7 V and f=948 MHz. Saturated and linear two-stage power modules operating at 900 MHz band with 31 dBm (1.25 W) output power have been demonstrated for analog and digital cellular applications respectively, the volume of which is as small as 0.4 cc. The saturated power module has achieved a PAE of 66% at V/sub d/=3.5 V, and the linear one has realized a PAE of 50% at V/sub d/=4.7 V.

A novel millimeter-wave IC on Si substrate using flip-chip bonding technology

A new MM-wave IC, constructed by flip-chip bonded heterojunction transistors and microstrip lines formed on Si substrate, has been proposed and demonstrated. Good agreements between calculated and measured characteristics of this new IC (named MFIC: millimeter-wave flip-chip IC) have been obtained up to 60 GHz band by using micro bump bonding technology. Several MFICs such as HFET/HBT amplifiers have been fabricated to confirm their designed performance.<<ETX>>

Advanced technologies of low-power GaAs ICs and power modules for cellular telephones

Low-power GaAs ICs and power modules have been developed for 150-cc-type cellular telephones. The front-end IC and power splitter IC can operate under 3 V, and the dissipation current is only half that of Si bipolar ICs. The front-end IC, consisting of a low-noise amplifier, local amplifier, and downconverter, shows a conversion gain of 22 dB at a local power of -15 dBm. The power splitter IC, used in dividing the output power of the voltage-controlled oscillator and supplying the local power to two mixers, shows an output power of 0 dBm and internal isolation of over 25 dB. The power module as a transmitter, composed of a two-stage hybrid amplifier using GaAs MESFETs, can operate at 4.7 V and deliver an output power of 1.5 W at f=950 MHz.<<ETX>>

AlGaAs/GaAs heterojunction bipolar transistors with small size fabricated by a multiple self-alignment process using one mask

A multiple self-alignment process for HBTs using one mask is developed to form emitters, emitter contacts, emitter contact leads, buried small collectors, base contacts, and base contact leads. This process makes it possible to produce HBTs of very small size and to reduce parasitic elements. An AlGaAs/GaAs HBT fabricated by the process, with an emitter 1 × 20/µm2in size and a buried collector by O+implantation gives a good performance of ft= 54 GHz and fmax= 42 GHz. The performance may be explained by the reduction of parasitic elements, base transit time, and collector depletion layer transit time.

A 3.5V, 1.3W GaAs power multichip IC for cellular phone

A GaAs power multichip IC (MCIC) operating at 3.5 V for cellular phone has been developed. The MCIC can deliver an output power over 1.3 W with a power-added efficiency of 60% from 890 to 950 MHz. It is comprised of two GaAs MESFETs, three GaAs passive matching chips and a printed board on which biasing networks are fabricated. These components are mounted on an aluminum nitride (AlN) package. The volume of the MCIC is only 0.4 cc, half that of conventional power hybrid ICs. This MCIC will contribute to realization of high performance and very compact cellular phones.<<ETX>>

A high power and high efficiency amplifier with controlled second-harmonic source impedance

A novel technology that drastically improves output power and efficiency of amplifiers has been developed. A record high 74% power added efficiency (PAE) with an output power (Pout) of 31.4 dBm (1.4 W) has been achieved from an ion implanted GaAs MESFET at a low supply voltage of 3.5 V and 930 MHz, by optimally terminating second-harmonic source impedance as well as second-harmonic load impedance. By using this technology, a small sized (0.4 cc) power amplifier module for cellular phones has been developed. It has realized a high PAE of 66% with Pout of 31 dBm (1.25 W) under the condition of 3.5 V around 915-945 MHz band.<<ETX>>

High isolation and low insertion loss switch IC using GaAs MESFET's

A novel RF switch IC using GaAs MESFETs has been developed for digital communication systems. The new IC is composed of a three-stage SPST switch and a thin film termination resistor, which realizes a high isolation and a low return loss. In addition, a high power handling capability and a low insertion loss are simultaneously realized with two kinds of pinch-off voltages using the orientation effect of GaAs MESFETs. According to these technologies, the excellent performance is achieved as follows: the isolation of 60 dB, the return loss of 20 dB, the 1 dB power compression of 27 dBm and the insertion loss of 1.6 dB at a frequency of 1.9 GHz with control voltages of 0/-5 V. The new switch IC contributes to a variety of communication system using high-quality digital modulation. >

Properties of molecular‐beam‐epitaxy‐grown and O+‐implanted GaAs and their application to the formation of a buried collector of an AlGaAs/GaAs heterojunction bipolar transistor

Changes in properties of molecular‐beam‐epitaxy‐grown GaAs by oxygen‐ion (O+) implantation and annealing, such as crystallinity, carrier concentration, and sheet resistance, are investigated. Using these results, we developed a method of O+ implantation through an external base area to form a small buried collector and to minimize the product, RbCbc, of the base‐collector capacitance Cbc and the base resistance Rb in an AlGaAs/GaAs heterojunction bipolar resistance Rb in an AlGaAs/GaAs heterojunction bipolar transistor (HBT) fabricated by a multiple self‐alignment process with one mask. High‐frequency properties of HBT’s are improved by this method remarkably.

Emitter&#8212;Base&#8212;Collector self-aligned heterojunction bipolar transistors using wet etching process

The first emitter-base-collector (EBC) self-aligned (SA) heterojunction bipolar transistors (HBTs) using wet etching process are described. This self-alignment fabrication technique is extremely simple but can get excellent high-frequency performance. An HBT with a 4-µm-wide emitter mesa showed 18 GHz of Ftand 13 GHz ofF_{\max}. By optimizing this process, high-frequency operation above 40 GHz can be expected.

Highly efficient, very compact GaAs power module for cellular telephone

A highly efficient and very compact power module using GaAs MESFETs has been developed for cellular telephones. The very-high-performance FETs, PPO (poly-phenylene oxide) printed board, and 1005-type chip C/Rs are mounted inside a very small frame of 0.8 cm/sup 3/. The load impedance of the first FET in the module is set at 50 Omega in order to satisfy the stability of the module to prevent oscillation. The typical RF properties of the module are as follows: an output power of 32.3 dBm and a power-added efficiency of 65% at a frequency of 930 MHz, an input power of 7 dBm, an operating voltage of 4.7 V.<<ETX>>