Kazukiyo Joshin

A 174 W high-efficiency GaN HEMT power amplifier for W-CDMA base station applications

AlGaN/GaN high electron mobility transistors (HEMTs) have been developed for current-collapse-free operation at high drain bias voltages. The newly designed single-chip GaN HEMT amplifier for W-CDMA base station applications achieves a record CW output power of 150 W with a high power-added efficiency (PAE) of 54% at 2.1 GHz. The amplifier, combined with a digital pre-distortion (DPD) system, also demonstrates a state of the art efficiency of 40% with an adjacent channel leakage power ratio (ACLR) of less than -50 dBc for 4-carrier W-CDMA signals and reaches the saturated peak power level of 174 W with a drain supply voltage of 63 V. We prove for the first time that the AlGaN/GaN HEMT amplifier can completely fulfills the W-CDMA system requirement.

An over 200-W output power GaN HEMT push-pull amplifier with high reliability

We describe a state-of-the-art 250-W output power AlGaN/GaN HEMT push-pull transmitter amplifier operated at a drain bias voltage of 50 V. We also demonstrated stable operation under RF stress testing for 1000 h at a drain bias voltage of 60 V, for the first time. The amplifier, combined with a digital pre-distortion (DPD) system, also achieved an adjacent channel leakage power ratio (ACLR) of less than -50 dBc for 1-carrier W-CDMA signals with a drain supply voltage of 50 V. We show, for the first time, that an AlGaN/GaN HEMTs push-pull amplifier can fulfill the requirements of W-CDMA systems.

Surface-charge controlled AlGaN/GaN-power HFET without current collapse and gm dispersion

We demonstrate high voltage HFET operation with suppression of gm dispersion and current collapse using an n-type thin GaN cap layer combined with SiN passivation and a recessed ohmic structure. Polarization-induced surface charge was controlled. Off state and on-state breakdown voltages were 140 V and 70 V. We obtained power HFETs with high CW operation voltage of 35 V without any heat sinking method.

A 77GHz transceiver in 90nm CMOS

CMOS technology is being advanced rapidly and applications are now expanding into the millimeter-wave regime on a global basis. 60GHz wireless systems in CMOS have already been reported [1]. In addition, 77GHz automotive radar is becoming the target for CMOS technology [2]. This paper describes what is believed to be the first transceiver chip for 77GHz radar in standard 90nm CMOS.

Thermal and source bumps utilizing carbon nanotubes for flip-chip high power amplifiers

Carbon nanotubes (CNTs) have been successfully developed as thermal and source bumps for flip-chip high power amplifiers (HPAs). The newly developed 15 mum long CNT bumps exhibit thermal conductivity of 1400 W/m-K. A flip-chip AlGaN/GaN HEMT HPA with a gate width of 2.4 mm utilizing CNT bumps, operating voltage of 40 V, exhibits an output power of 39 dBm at, a frequency of 2.1 GHz without any degradation due to heat-up. To our knowledge, this is the first report about, a practical application of CNTs using their high thermal conductivity

42% high efficiency two-stage HBT power amplifier MMIC for W-CDMA cellular phone system

This paper is the first to report a high efficiency two-stage HBT power amplifier MMIC for 1.95 GHz wide-band CDMA (W-CDMA) cellular phone system. Power amplifiers for W-CDMA system are required with high efficiency and high linearity over a wide range of output power level. To obtain a high efficiency, we chose a near class B operation. To obtain a high linearity, we suppressed the gain distortion due to a near class B operation by the adaptive biasing technique. The MMIC exhibited the highest power-added efficiency (PAE) of 42% ever reported, a gain of 30.5 dB, and an adjacent channel leakage power ratio (ACLR) it a 5 MHz offset frequency of -38 dBc at a Pout of 27 dBm under a supply voltage of 3.5 V with 3.84 Mcps HPSK modulation.

1.5 V Low-Voltage Microwave Power Performance of InAlAs/InGaAs Double Heterojunction Bipolar Transistors

In this paper, we report the first demonstration of microwave power performance of InAlAs/InGaAs double heterojunction bipolar transistors (DHBTs) obtained at an extremely low operating voltage of 1.5 V. In order to obtain a high output power (P out) at a low operating voltage, we used DHBTs rather than single heterojunction bipolar transistors (SHBTs) and thus reduced the offset voltage (V CE,offset). We obtained a much lower V CE,offset of 50 mV for the DHBT than that of 300 mV for a SHBT. At a low operation voltage of 1.5 V, the DHBT exhibited a P out of 20.6 dBm with a power added efficiency (η add) of 36.6% and a power gain (G a) of 8.5 dB biased for class-B operation at 1.9 GHz. The high-speed performance of the DHBT are a unity cutoff frequency (f T) of 76 GHz and a maximum oscillation frequency (f max) of 157 GHz. We also studied the reliability of DHBTs by conducting a 1000-hour accelerated life test. The InGaAs HBTs had a lifetime of 2×106 h at a junction temperature of 125°C with an activation energy of 0.95 eV.

C-band 340-W and X-band 100-W GaN power amplifiers with over 50-% PAE

In this paper, we report a C-band power amplifier with over 340-W output power using 0.8-µm GaN-HEMTs and an X-band power amplifier with over 100-W output power using 0.25-µm GaN-HEMTs. We used two-chip configurations and the three-stage impedance transformers to extend the bandwidth for both circuits. The input and output lines adjacent to each chip are divided by four to suppress the non-uniform heat distribution in a chip at high frequencies. As a result, we obtained 343-W output power and 53-% power added efficiency (PAE) at 4.8 GHz. This is the highest output power ever reported C-band power amplifiers. We also obtained 101-W output power and 53-% PAE at 9.8 GHz. This is also the highest PAE ever reported X-band power amplifiers with over 50-W output power.

Reliability of GaN HEMTs: current status and future technology

In this paper, we describe highly reliable GaN high electron mobility transistors (HEMTs) for high-power and high-efficiency amplifiers. First, we present the reliability mechanisms and progress on the previously reported GaN HEMTs. Next, we introduce our specific device structure for GaN HEMTs for improving reliability. An n-GaN cap and optimized buffer layer are used to realize high efficiency and high reliability by suppressing current collapse and quiescent current (Idsq)-drift. Finally, we propose a new device process around the gate electrode for further improvement of reliability. Preventing gate edge silicidation leads to reduced gate leakage current and suppression of initial degradation in a DC-stress test under high-temperature and high-voltage conditions. Gate edge engineering plays a key role in reducing the gate leakage current and improving reliability.

63.2% high efficiency and high linearity two-stage InGaP/GaAs HBT power amplifier for personal digital cellular phone system

This paper reports on a high efficiency and high linearity two-stage InGaP/GaAs heterojunction bipolar transistor (HBT) power amplifier for the Japanese personal digital cellular phone system (PDC). Our power-stage HBT amplifier exhibited a high power added efficiency (PAE) of 68.8% and an adjacent channel leakage power (ACP) of -48 dBc. The ACP of the two-stage amplifier was improved enough for PDC with keeping a high PAE by combining of a driver-stage and this power-stage amplifiers. Our two-stage HBT power amplifier exhibited the highest PAE of 63.2% ever reported and an ACP at a 50-kHz offset frequency of -52 dBc in 1.5 GHz PDC standard at a Pout of 31 dBm under a supply voltage of 3.5 V.