Tohru Oka

AlGaN/GaN Recessed MIS-Gate HFET With High-Threshold-Voltage Normally-Off Operation for Power Electronics Applications

This letter reports normally-off operation of an AlGaN/GaN recessed MIS-gate heterostructure field-effect transistor with a high threshold voltage. The GaN-based recessed MIS-gate structure in conjunction with negative polarization charges under the gate allows us to achieve the high threshold voltage, whereas the low on-state resistance is maintained by the 2-D electron gas remaining in the channel except for the recessed MIS-gate region. The fabricated device exhibits a threshold voltage as high as 5.2 V with a maximum field-effect mobility of 120 cm2/Vmiddots, a maximum drain current of over 200 mA/mm, and a breakdown voltage of 400 V.

A High-Power Low-Distortion GaAs HBT Power Amplifier for Mobile Terminals Used in Broadband Wireless Applications

This paper describes technologies of miniaturized high-power low-distortion GaAs HBT power amplifiers with a low-voltage operation for mobile terminals used in 5-6 GHz broadband wireless applications. In conjunction with diode-based linearizing techniques, wideband matching network techniques including trap circuits for second harmonics allow us to obtain a compact broadband power amplifier module with harmonic filtering, achieving the high linear output power at a low supply voltage together with the low distortion and the low second-harmonic spurious outputs in a wide frequency range. The fabricated power amplifier exhibited linear output power levels of 21 and 22 dBm at EVM values of 2.0 and 3.0%, respectively, measured with 54 Mb/s 64-QAM-OFDM signals at a supply voltage of 3.3 V in a frequency range of 5-6 GHz. Second harmonic spurious outputs below -35 dBc were also attained.

A 5 GHz high efficiency and low distortion InGaP/GaAs HBT power amplifier MMIC

An InGaP/GaAs two-stage HBT power amplifier for 5 GHz Wireless-LAN applications was developed. By using a self-aligned base contact formation process and an external base region side etching process, a high gain HBT was realized. A small-sized via hole fabrication process was developed. The gain of multi-finger HBT was improved by locating via holes between each finger. Linearity was also improved by developing a new variable negative feedback circuit. A power amplifier MMIC utilizing this technology was fabricated, and 19.7 dBm output power, 22 dB gain, 22.5% power-added-efficiency (PAE), 5.0% error vector magnitude (EVM) were obtained at 54 Mbps transmission under a supply voltage of 3.3 V. These state of the art data represent the highest PAE reported for a the power amplifier MMIC in the 5 GHz Wireless-LAN application.

Enhanced linearity and efficiency of HBT power amplifiers for 5-GHz wireless-LANs

This paper describes two advanced techniques to enhance linearity and efficiency in HBT power amplifiers (PA) for 5-GHz wireless-LANs (W-LANs). The diode-based linearizing circuit successfully compensates the gain expansion of PAs operating at a low quiescent current. The output matching circuit consisting of on-chip MIM capacitors and bond wires effectively reduces the loss of the circuit as well as allowing the miniaturization of the PA module. The PA MMIC fabricated incorporating these techniques achieved an improvement in linear output power and PAE of 2.4 dBm and 4.8%, respectively, compared to our previous PA with the same device dimensions, and exhibited an output power of 22.1 dBm and a PAE of 27.3% at an EVM of 5%, measured with 54Mbps 64-QAM-OFDM signals at 5.25 GHz.

High-performance InGaP power HBT technologies for wireless applications

We review the technological features of our InGaP power HBTs for 5GHz wireless application. The features include self-aligned base-contact and base-mesa formation process, small-sized via holes located between multi-finger transistors, and bias and feedback circuits for the reduction of distortion. These technologies improve both gain and linearity, producing higher power added efficiency (PAE) in power amplifiers.

A High-Power Low-Distortion GaAs HBT Power Amplifier with 3.3 V Supply for 5-6 GHz Broadband Wireless Applications

This paper describes a 5-6 GHz band GaAs HBT power amplifier operating at 3.3 V for broadband wireless applications. In conjunction with linearizing circuit techniques, wideband matching circuits including trap circuits for 2nd harmonics allow us to achieve the high linear output power and the low distortion together with low 2nd-harmonic spurious outputs. The fabricated power amplifier exhibited linear output power levels of 21 and 22 dBm at EVM values of 2.0 and 3.0%, respectively, measured with 54 Mbps 64-QAM-OFDM signals. The 2nd harmonic spurious outputs below -35 dBc were also attained

SiGe HBT power amplifier with distortion-controllable bias circuit and its application to 802.11g wireless LANs

This paper describes a SiGe HBT power amplifier with distortion-controllable bias circuits. MOSFETs employed in the bias circuits enable us to control the distortion of power amplifiers by adjusting the gate voltages. The power amplifier MMIC for 802.11lg wireless LANs fabricated using the technique exhibited excellent linearity and efficiency: a linear output power of 18.3 dBm and a power-added efficiency of 16% were achieved at an EVM of 3%, measured with 54 Mbps 64-QAM OFDM signals at 2.45 GHz.