Masafumi Shigaki

One-chip GaAs monolithic frequency converter operable to 4 GHz

The frequency converter combines a feedback amplifier, a differential amplifier, a double-balanced mixer, a voltage-controlled oscillator, and an IF amplifier on a 1-mm/sup 2/ GaAs chip. The FET circuits were matched by digital IC design rather than by the distributed element network technique, to use the substrate more effectively. Self-aligned WSi/Au gates 1.5 mu m long were used, and the resistance in conventional WSi gates was reduced to enhance microwave characteristics. At 4 GHz, the conversion gain is 18 dB, the double-sideband noise is 11.8 dB and the output power is 5.6 dBm. >

An On-Board 50 GHz Band Low-Noise Amplifier for Millimeter Wave Personal Satellite Communications

An onboard 50 GHz band low-noise amplifier for millimeter wave personal satellite communications is developed. A 100-¿ m-wide and 0.25-¿ m-long gate HEMT is developed. An accurate S parameter of a device with bonding wire is successfully measured up to 40 GHz using MMIC technology. The characteristics of this amplifier are a 20 dB gain, 4.2 dB noise figure, and 20 dB input return loss over a 50.4 GHz to 51.4 GHz communication bandwidth at room temperature. At +60°C and ¿40°C, the maximum noise figures are 4.4 dB and 2.8 dB, respectively. There are no problems for the temperature cycle and modal survey test.

38-GHz Band High-Power MMIC Amplifier Design using Improved Load-Pull Method

To facilitate accurate amplifier design, the large-signal impedance of a GaAs FET with a 0.25-¿m-long gate was measured using an improved load-pull method. A new MMIC transformer was used in the measurement to transform the FETs impedance into the coverage range of a twin sleeve tuner. The transformer as well as a wafer prober improved measurement accuracy. Two types of high-power amplifiers were designed using the measured large-signal impedance: one is composed of four FET cells with 400-¿m-wide gates and the other is composed of two FET cells with 600-¿m-wide gates. At 38 GHz and at 1-dB gain compression level, the former has an output power of 25.1 dBm and the latter 23.5 dBm.

High-speed GaAs dynamic frequency divider using a double-loop structure and differential amplifiers

GaAs 2.0-8.0-GHz and 6.0-10.5-GHz dynamic frequency dividers have been developed. These dynamic dividers have a double-loop structure using a differential amplifier for high-speed and stable operation despite supply-voltage fluctuations. This structure operates from a single voltage supply. An advanced WSi self-aligned gate process technology (0.1- mu m long gate) was used to improve the high-frequency characteristics of the FET. >

An on-board 47-GHz phose-locked oscillator using FET gate bias control for low phase noise

We have developed an on-board 47-GHz phase locked oscillator (PLO) for millimeter-wave personal satellite communications system. For low phase-noise operation, we developed an osciplier using PET gate bias control technique, and used a sampling phase detector. We developed a noise addition model for accurate design. The phase noise of this 47-GHz PLO was an exceptionally low ¿63, ¿85, and ¿100 dBc/Hz at offset frequencies of 100 Hz, 1 kHz, and 100 kHz.

38-GHz-band high-power MMIC amplifier module for satellites on board use

The design and development results of 38-GHz high-power MMIC amplifier modules for use in the solid-state power amplifier (SSPA) to be carried aboard Engineering Test Satellite VI in 1993 are presented. This amplifier will be used in millimeter-wave intersatellite communication experiments. For the development of this amplifier, high-power, highly reliable FETs with 0.25- mu m-long gates were designed. The FET large-signal impedance was accurately measured using an improved load-pull method and MMIC transformers. The measurements were used to design two types of MMICs: one composed of two FET cells with 600- mu m-wide gates and the other of four FET cells with 400- mu m-wide gates. A two-stage amplifier package consisting of two of these MMICs that can be used at 38 GHz is also developed. A P/sub o/(1 dB) of 25 dBm and a gain of 11 dB are obtained. A 38-GHz test conducted during chip screening achieves a high production yield without circuits adjustment. >

Design for a Superconducting Filter Front-End

We propose a front-end with a combination of a circulator and receive and transmit superconducting filters (SCFs) for applications to the base stations of the future generation wireless communications. Ideally, all superconducting filters used are desirable. We made and estimated a preliminary front-end model with a volume of 43 liters using a duplexer, superconducting filters, and a cryo low noise amplifier (LNA), etc. for 5GHz band recently. In the preliminary model, noise figure (NF) had 2.0 dB or lower, and the transmit SCF endured over 10W. The measured normal duplexer showed that between the receive and transmit channels with 100MHz bandedge separation was isolated to be 30dB, which is not enough for practical use. It was found that the combination of a circulator and receive and transmit SCFs can improved the isolation to 80dB or more. Besides, we designed a new compact front-end that reduce the volume to the target value of 15 liters. To reduce the volume, the cryo-cooler and the dewar with a vacuum chamber, and other RF components needs to be miniaturized. Therefore, we selected the circulator instead of the duplexer.

GaAs Monolithic DC-6.4-GHz Variable-Gain Feedback Amplifier (Short Paper)

A GaAs dc-6.4-GHz variable-gain two-stage feedback amplifier with 11 dB gain has been developed. The wide bandwidth is achieved by combining a microwave matching circuit with a direct-coupled circuit. This design improves the bandwidth significantly. This circuit also has a reduced chip size. Since no interstage capacitor is necessary, the chip size is only 0.5 x 1.5 mm/sup 2/. Active resistance was used in the second stage feedback circuit for variable gain. Au/ WSi self-alignment technology with a 1-µm gate length was used to improve the high-frequency characteristics of the FET.

GaAs Monolithic Astable Multivibrator Type VCO Operable up to KU Band

The estimated theoretical limit to oscillation frequency predicts that the frequency of a GaAs monolithic astable multiviblator type oscillator can be increased from the maximum reported frequency of 5 GHz to 17 GHz by optimization of circuit parameters. The increase is made possible by the W-silicide self alignment process due to its precision processing and high uniformity of FETs within a wafer. This type of oscillator is suitable for use as the local oscillator in monolithic front ends because it can be coupled directly with a double balanced mixer or prescaler without any phase shift circuits. Its simultaneous production of 0° and 180° phase output has made it possible to fabricate the VCO and prescaler on one chip. The operation of this chip is confirmed up to 2 GHz which is the upper limit frequency of the prescaler.

Frequency and power saving of the future generation wireless communications by superconducting filter

This paper proposes a model for further effective use of frequency and power of the future generation wireless communications by superconducting filter. The transmit amplifier SSPA (solid state power amplifier) has conventionally been used at its linear region by taking enough back-off in order to compress the out-band spectrum spreading. We constituted a computer simulation for the evaluation of the transmission performance of OFDM (orthogonal frequency division multiplexing) modulation in the nonlinear channel of SSPA with the sharp transmit filter of superconducting filter for 5 GHz band base station including fading. As the result of the simulation, we can save 3-5 dB of the SSPA power in the model. Moreover, the channel interval can be reduced by about 30% in frequency by the steep attenuation outside band characteristics. It is expected that the SSPA can be with small back-off and also advantageous in power consumption by using the superconducting filter.