high frequency device

High-Frequency Semiconductor Devices for Mobile Phones 74

High-Frequency Semiconductor Devices for Mobile Phones

OVERVIEW: The dissemination of mobile phones is proceeding at a rapidpace throughout the world. This trend has been driven by smaller size andlighter weight, and by the much lower price that has become possible becauseof technological innovation in components—especially semiconductors.Achieving smaller size, lighter weight, lower price, and longer talk-timeare unchangeable propositions, and even now technological innovationproceeds step by step. At present the progress being made in bringing higherfunctionality to mobile phones is leading to an increase in componentsincluding semiconductors. This in turn tends to cause an increase in powerconsumption. Also, to increase convenience of use, dual-band types anddual-mode types are being implemented, decreasing the space available forthose components. This further increases requirements that semiconductorsbecome smaller, thinner, and operate with lower power consumption. Hitachi,Ltd. has responded to these needs by developing and producing a variety ofhigh-frequency semiconductor devices for mobile phones. These includepower amplifiers with high efficiency and low power consumption, GaAsmicrowave monolithic ICs (MMIC) that can be densely integrated andbipolar complementary metal-oxide semiconductor (Bi-CMOS) analogsignal processing ICs for dual-band operation.Chushiro Kusano

Tetsuaki Adachi

Takefumi Endo

Shigeyuki Sudo

INTRODUCTION

REQUIREMENTS for mobile phones, which enable

anyone to communicate anytime at anyplace, include

small size, light weight, and long talk-time. Smaller

size and lighter weight can be implemented byintegrating semiconductors more densely and using

smaller packages. Long talk-time has been made

possible by the higher efficiency and performance of

semiconductors, which results in longer battery life.

In this paper we will discuss mobile phone systems

Fig. 1—Principal High-FrequencySemiconductors for Mobile Phones.Three dual-band circuits were developedand are now being produced. The compactlydesigned dual-band high-frequency poweramplifier module features a small packageand high efficiency in each band. The dual-band receiver section is a composite GaAsMMIC consisting of a low-noise amplifier,mixer circuits, and local oscillator amplifierwith on-chip input and output matchingcircuits in a small surface-mount package.The dual-band high-frequency analog signalprocessing IC incorporates most of therequired high-frequency receiver andtransmitter analog functions implementedon-chip in a small package.

(c) GaAs MMIC low-noise amplifier, mixer circuit, and local-oscillator amplifier(a) Si-MOSFET dual-band high-frequency power amplifier module

(b) Bi-CMOS dual-band high frequency analog signal processing ICMOSFET: metal-oxide semiconductor field-effecttransistorHitachi Review Vol. 48 (1999), No. 2 75

TABLE 1. Principal Communication Systems for Digital Mobile PhonesPDC is used in Japan, GSM has its hub in Europe but extends to a total of more than 100 countries,and N-CDMA is used in Asia including Japan, and in the US. W-CDMA has been proposed by Japanas a candidate for IMT-2000.trends and requirements. We will also describe the high

efficiency, high performance, and high-integration

technology of high frequency semiconductor devices

developed by Hitachi together with the outlook for

the future.

SYSTEM TRENDS AND REQUIREMENTS

Mobile phones are undergoing a generation change

from the analog types that were called the first

generation to the second generation digital types that

have become predominant. The principal second

generation communications systems are shown in

Table 1.

Conversations cannot be carried out between

mobile phones using different communications

systems. Thus, for convenience, manufacturers are

making dual mode types - code division multiple

access (CDMA) and Advanced Mobile Phone Service

(AMPS), etc.; and dual band types - Global System

for Mobile Communications (GSM) and Digital

Cellular System 1800 (DCS-1800), etc.

The communications area of mobile phones is

confined to within a limited area on land, but systems

such as Iridium using low earth-orbit communications

satellites circling the earth will provide seamlessworldwide communications so that conversations will

be possible at anyplace with a single mobile phone.

If one uses a dual-mode mobile phone, one can

change the mode of operation to utilize satellite service

when in an area beyond the reach of terrestrial signals.

These services feature the use of low earth orbit

circling satellites: thus the distance to the earth is small,