Yoichiro Takayama

A Highly Stabilized Low-Noise GaAs FET Integrated Oscillator with a Dielectric Resonator in the C Band

A GaAs FET integrated oscillator stabilized with a BaO--TiO/sub 2/ system ceramic dielectric resonator provides a high-frequency-stabilized low-noise compact microwave power source. The newly developed ceramic has an expansion coefficient and dielectric constant temperature coefficient that offset each other and result in a small resonant frequency temperature coefficient. A stabilized oscillator output of 100 mW with a 17-percent efficiency and a frequency temperature coefficient as low as 2.3 ppm//spl deg/C are obtained at 6 GHz. FM noise level is reduced more the 30 dB by the stabilization. The dynamic properties of the oscillator and resonator are precisely measured to determine equivalent circuit representations. A large-signal design theory based on these equivalent circuit representations is presented to realize the optimal coupling condition between the oscillator and stabilizing resonator. The stabilized oscillator performance is sufficient for application to microwave communications systems.

DC-110-GHz MMIC traveling-wave switch

This paper presents the broadest band monolithic-microwave integrated-circuit traveling-wave switch ever reported for millimeter-wave applications. The developed switch with the novel structure of a 400-/spl mu/m-gate finger field-effect transistor (FET) indicated an insertion loss of less than 2.55 dB and an isolation of better than 22.2 dB from dc to 110 GHz. Also, the switch indicated no degradation of insertion loss and an ON/OFF ratio of more than 22.7 dB up to an input power of 26.5 dBm at 40 GHz. Circuit analytical results based on a lossy transmission-line model for small-signal performance and circuit simulation results using the two-terminal nonlinear FET model for large-signal operation successfully showed good agreement with the experimental results.

A high-power GaAs MESFET with an experimentally optimized pattern

A high-power GaAs MESFET with a high packing density has been developed in order to increase the total gatewidth within limited practical device size. The gate-finger width was experimentally optimized to increase the packing density without deterioration of the power gain. The developed power MESFET is the crossover structure and has a total gatewidth of 15 mm with gate-finger width of 190 µm in a 2.2-mm-wide chip. The packing density was almost doubled, and the output powers of 25 W at 6 GHz, and 17 W at 8 GHz were obtained from the internally matched four-chip devices.

Dual-band GaAs FET power amplifier with two-frequency matching circuits

A dual-band GaAs FET power amplifier with the two-frequency lumped-element matching circuits is designed using the low-pass Chebyshev-form impedance transformer design method. An 800/1500MHz 1Watt-class GaAs FET amplifier is fabricated and the experimental results show the saturated output powers of 30.9dBm and 28.2dBm with the power added-efficiencies of 51.6% and 51.9% at 800MHz and 1500MHz, respectively. The fabricated circuit size is 24mm by 28mm. The presented design approach enables a simple dual-band power amplifier with superior performance and small size.

A High-Efficiency Low-Distortion GaN HEMT Doherty Power Amplifier With a Series-Connected Load

A distortion reduction method for a newly developed GaN HEMT Doherty amplifier (DA) with a series-connected load operating at 1.8 GHz is presented. Differing from conventional DAs with shunt-connected loads, the newly developed DA with a series-connected load has high input impedance, resulting in low-loss impedance matching and high-efficiency power combining. A distortion cancellation mechanism and its condition are derived, where odd-order nonlinear factors of transistors are considered, so as to retain inherent distortion cancellation between a peaking amplifier and a carrier amplifier. The validity of the design method is demonstrated using the developed 1.8-GHz GaN HEMT DA with a series-connected load. The third-order intermodulation distortion of the DA is improved by more than 15 dB at output powers from 5 to 20 dBm, compared to the case giving priority to power efficiency. The developed amplifier delivers a power-added efficiency (PAE) of 31% at an output power of 24 dBm, corresponding to 10-dB input backoff from a saturated output power of 31 dBm with a PAE of 58%. The proposed distortion reduction method can also be applied to shunt-connected-load-type amplifiers of other devices.

Broad-Band Internal Matching of Microwave Power GaAs MESFET's

Broad-band internal matching techniques for high-power GaAS MESFETs at C band have been developed adopting novel circuit configurations and large-signal characterizations in the circuit design. The lumped-element two-section input matching network is formed on a single ceramic plate with a high dielectric constant. The semidistributed single-section output circuit is formed in microstrip pattern on an alumina plate. The internally matched GaAs FET with 11200-mu m total gate width developed has a 2.5-W power output at 1-dB gain compression and a 4.4-W saturated power output with 5.5-dB linear gain from 4.2 to 7.2 GHz without external matching. The FET internally matched from 4.5 to 6.5 GHz exhibited 5-W saturated power output with 6-dB linear gain.

Doppler Signal Detection with Negative-Resistance Diode Oscillators

A theory is presented for the Doppler signal detection with a negative-resistance diode oscillator operating simultaneously as a signal source and Doppler signal detector. The theory is based on a realistic model of the oscillator, including an object passing in front of an antenna, and includes the previous treatments as the limiting cases. The effect of the bias circuit taking out the Doppler signal on the RF operation of the oscillator is taken into account self-consistently. The frequency down-conversion with a free-running oscillator is also investigated. Conversion gain is demonstrated by the experiment using a Gunn oscillator with a movable load.

A GaN HEMT Doherty amplifier with a series connected load

Doherty introduced two types of concepts for high-efficiency amplifiers in 1936. One involved a shunt connected load and the other involved a series connected load. The first one is well known. We propose a microwave Doherty power amplifier with a series connected load using baluns. A 1.9 GHz GaN HEMT Doherty power amplifier was designed and fabricated. At 24 dBm middle and 31 dBm saturated output powers, the amplifier realized improved power efficiencies of 31 % and 56 %, respectively, compared to power efficiencies of 15 % at 24 dBm output power and 57 % at 34 dBm saturated power, respectively, obtained with a reference push-pull amplifier.

Design Considerations for Traveling-Wave Single-Pole Multithrow MMIC Switch Using Fully Distributed FET

The circuit design considerations for the traveling-wave switch (TWSW) single-pole double-throw (SPDT) monolithic microwave integrated circuit (MMIC) utilizing a fully distributed FET (FD-FET) are presented here for the first time. The normalized length of the impedance transformer for a single-pole multithrow TWSW using the FD-FET is found to be less than a quarter-wavelength at the operating frequency. Unlike the TWSW using lumped FETs, the TWSW with the FD-FET offers the advantage of no design limits regarding such frequency characteristics as bandwidth and group delay. The newly developed SPDT TWSW MMIC using the 400-mum-gate finger FD-FET delivers broadband characteristics over more than an octave frequency range with highly reliable MMIC technology. The newly developed SPDT MMIC switch provides low insertion loss of less than 2.1 dB and high isolation of over 25.5 dB from 38 to 80 GHz, coupled with the benefit of very small size

1.2 V operation power heterojunction FET's for digital cellular applications

This paper describes 950 MHz power performance of 1.2 V drain bias operation n-AlGaAs/InGaAs/n-AlGaAs heterojunction FETs (HJFET) for personal digital cellular (PDC) applications. The fabricated HJFET with a 0.8-/spl mu/m long WSi gate exhibited an on-resistance (/spl tau//sub 0n/) of 2.1/spl Omega//spl middot/mm and a maximum drain current of 640 mA/mm. Operated at 1.2 V drain bias voltage, the HJFET with gate width of 28.0 mm demonstrated an output power of 30.0 dBm (1.0 W) and a power-added efficiency of 51.5% with an adjacent channel leakage power at 50 kHz off-center frequency of -50.8 dBc. Class A operation analysis, which shows a good coincidence with the measured PDC power performance, revealed that the excellent power performance with the relatively small gate width was due to the low /spl tau//sub 0n/ of the fabricated HJFET.