The base transit time of an Aluminum-graded-base PNp AlGaAs/GaAs heterojunction bipolar transistor (HBT) was studied in order to clarify the effect of aluminum grading in the base. Theoretical analysis using a classical drift diffusion model with velocity saturation at the base-collector junction and a high base quasielectric field (58 keV/cm) created by 20%-aluminum linear grading in a 400 base, leads to a base transit time (τb) of 0.9 ps. The base transit time is reduced by four times, compared to the base transit time of 3.6 ps without aluminum grading in the base. In order to demonstrate this advantage, we fabricated aluminum-graded-base PNp AlGaAs/GaAs heterojunction transistor which employs a 20%-aluminum linear graded 400 -wide base. The device with a 2 µm 10 µm emitter showed high RF performance with a cut-off frequency (ft) of 37 GHz and a maximum oscillation frequency (fmax) of 30 GHz at a collector current density of 3.4 104 A/cm2. Further analysis using direct parameter extraction of a small signal circuit model under the collector current density of 1.1-9.9104 A/cm2 indicated the intrinsic transit time, which is the sum of the base transit time and the collector depletion layer transit time (τSC), was as low as 2.3 ps under lowinjection level. Subtracting the collector depletion-layer transit time from the intrinsic time leads to a base transit time of 1.1 ps, which is close to the theoretical base transit time and is the shortest value ever reported. The structure is very attractive for pnp-type AlGaAs HBTs combined with Npn HBTs for complementary applications.

A GaAs power MESFET amplifier with a low-distortion, 10-dB gain-variable attenuator has been developed for 1. 9-GHz Japanese personal handy phone system (PHS). Independently of its gain, a very low 600-kHz adjacent channel leakage power (ACP) with sufficient output power was attained. In single low 2. 4-V supply operation, an output power of 21. 1 dBm, a low dissipated current of 157 mA and a high power-added efficiency (PAE) of 37. 2% were obtained with an ACP of -55 dBc.

This paper describes an ultralow-power multi-threshold (MT) CMOS/SOI circuit technique that mainly uses fully-depleted MOSFETs. The MTCMOS/SOI circuit, which combines fully-depleted low- and medium-Vth CMOS/SOI logic gates and high-Vth power-switch transistors, makes it possible to lower the supply voltage to 0.5 V and reduce the power dissipation of LSIs to the 1-mW level. We overview some MTCMOS/SOI digital and analog components, such as a CPU, memory, analog/RF circuit and DC-DC converter for an ultralow-power mobile system. The validity of the ultralow-voltage MTCMOS/SOI circuits is confirmed by the demonstration of a self-powered 300-MHz-band short-range wireless system. A 1-V SAW oscillator and a switched-capacitor-type DC-DC converter in the transmitter makes possible self-powered transmission by the heat from a hand. In the receiver, a 0.5-V digital controller composed of a 8-bit CPU, 256-kbit SRAM, and ROM also make self-powered operation under illumination possible.

We report on 1.9-GHz performance of the Buried-Channel self-aligned WN/W-gate GaAs MESFET (BC-MESFET) for use in digital mobile telephone handsets with low power consumption. The BC-MESFET incorporates undoped i-GaAs epitaxial-grown surface layer on the ion-implanted channel. Both the power and noise performance of the BC-MESFET are superior to the conventional MESFET. The 0.6-µm gate power BC-MESFET exhibits a high power-added efficiency of 57% at 1-dB gain compression, which leads to low power dissipation of the handset. This power performance is attributed to high breakdown voltage which the undoped i-GaAs surface layer has brought about. The BC-MESFET has also shown a minimum noise figure of below 0.4 dB. Taking the IC-oriented fabrication process of the BC-MESFET into consideration, these FET performances demonstrate that the BC-MESFET is suitable for the single-chip MMIC that integrates RF front-end blocks for the 1.9-GHz small-size mobile telephone handset with long battery lifetime.

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 GaAs SPDT switch IC operating at a low power supply voltage of 2.7 V has been developed for use in 1.9 GHz band personal handy phone system (PHS). In combination with MESFETs with low on-resistance and high breakdown voltage, the switch IC adopts parallel-LC resonant circuits and utilizes both stacked FETs and an additional shunt capacitor at the receiver side in order to realize low insertion loss, high isolation and low distortion characteristics. An insertion loss of 0.55 dB and an isolation of 35.8 dB were obtained at 1.9 GHz. The IC also achieved an output power of 25.0 dBm at 1 dB gain compression point, a second order distortion of -54.3 dBc and an adjacent channel leakage power of -66 dBc at 600 kHz apart from 1.9 GHz at 19 dBm output power.

Two approaches to the design of resonant-type switches with low distortion characteristics operating at a 2-V power supply voltage have been proposed for use in the 1. 9-GHz-band personal handy phone system (PHS). One approach is to use three stacked FETs at the receiver side. They are composed of a dual-gate FET and a single-gate FET. An insertion loss of 0. 41 dB and an isolation of 44. 0 dB were obtained at 1. 9 GHz. A third-order distortion value of -52 dBc was achieved at 19 dBm output power. Another approach is to insert a capacitor in the resonator. A third-order distortion of -49 dBc at 19-dBm output power when two stacked FETs were used at the receiver side. The layout area of the resonator is drastically reduced as compared with the above-mentioned case.