T. Takagi

A C-band AlGaN/GaN HEMT with Cat-CVD SiN passivation developed for an over 100 W operation

We applied a Cat-CVD (catalytic chemical vapor deposition) passivation film to AlGaN/GaN HEMTs, to resolve the trade-off between their drain current transient time and gate-drain break down voltage. We did not employ any field plate because it degrades high frequency operation over C-band. The SiN passivation film, deposited after a NH 3 treatment, resulted in less transient time and less gate leakage current than conventional PE-CVD passivation. A T-shaped gate HEMT fabricated by this technique, with Lg = 0.4 μm and Wg = 50.4 mm, delivered an output power over 140 W (2.79 W/mm), which was a record power at C-band.

A Ka-Band GaAs Power MMIC

A Ka-band GaAs power MMIC with source island via-hole PHS structure and monolithic power divider /combiner circuits was developed and reliability study was performed. This source island via-hole technique successfully reduced both thermal resistance and source parasitic inductance of the MMIC. The 3200 µm MMIC gave power output at 1dB gain compression of 1.1 W, linear power gain of 4.0 dB and power added efficiency of 10.8 % at 28 GHz. No failure was observed in the temperature cycling, the DC running and the high temperature storage tests.

An even harmonic mixer using self-biased anti-parallel diode pair

This paper presents a novel even harmonic mixer using self-biased anti-parallel diode pair (APDP). Resistors for self-bias are employed in APDP, and voltage differences in D.C. arise at each diode when LO power is applied. As increasing of LO power, voltage differences become larger, so maximum voltages of LO wave added to each diode are almost constant and conversion loss of the mixer is kept constantly. In the developed L-band even harmonic mixer using self-biased APDP for a direct conversion receiver, fluctuation of voltage conversion gain is below 1 dB with LO power of from 0 dBm to 14 dBm.

A UHF band 1.3 W monolithic amplifier with efficiency of 63

A UHF-band 1.3-W high-efficiency, four-stage monolithic power amplifier with a novel miniaturized second-harmonic terminating circuit was developed. With the use of a parallel resonant circuit composed of lumped elements for terminating the second harmonic, it achieved a maximum drain efficiency of 63% and a saturated output power of higher than 31 dBm in the UHF band, and it occupied an area of 8.6*5.8 mm.<<ETX>>

A 1.9 GHz single-chip RF front-end GaAs MMIC with low-distortion cascode FET mixer for personal handy-phone system terminals

This paper describes new single-chip RF front-end GaAs MMIC for 1.9 GHz Japanese PHS handheld terminals. The IC consists of a high power amplifier, a T/R switch, a low noise amplifier, a newly developed low distortion cascode FET mixer and a negative voltage generator for FET gate bias voltage. The IC has high performance as an RF front-end for PHS terminals.This paper describes new single-chip RF front-end GaAs MMIC for 1.9 GHz Japanese PHS handheld terminals. The IC consists of a high power amplifier, a T/R switch, a low noise amplifier, a newly developed low distortion cascode FET mixer and a negative voltage generator for FET gate bias voltage. The IC has high performance as RF front-end for terminals.

Efficiency Enhancement of 250W Doherty Power Amplifiers Using Virtual Open Stub Techniques for UHF-band OFDM Applications

We propose a new efficiency enhancement method of Doherty power amplifiers (PAs) using virtual open stub techniques. In this method, we consider a peak amplifiers output line as a virtual capacitive open stub only seen at low power level. Using this method, we can transform the low power load impedance seen from the carrier amplifier into higher than the impedance of classical Doherty PA (>100ohm). The relations of the load impedance and the length of the virtual open stub are derived analytically. The developed UHF-band 250W 2-way Doherty PA has been achieved a drain efficiency of 42.1% and an intermodulation (IM) distortion of -27.3dBc at an output power of 44.1dBm (10dB output backed-off) under an integrated services digital broadcasting-terrestrial (ISDB-T) OFDM signal. To the best of our knowledge, these results are the highest backed-off efficiency ever reported among the over 40dBm saturation high power Doherty amplifiers

1.9 GHz/5.8 GHz-band on-chip matching Si-MMIC low noise amplifiers fabricated on high resistive Si substrate

The use of high resistivity Si substrates, instead of the conventional low resistivity Si substrate, enables one to reduce the loss of spiral inductor for the on-chip matching circuit by 61% at 1.9 GHz and by 78% at 5.8 GHz and to improve gain and noise performance of the BJT. These improvements are explained as the reduction of dielectric loss of substrate by referring to equivalent circuit model extraction. The fabricated 1.9 GHz-band on-chip matching LNA performs 13.4 dB gain, 1.9 dB NF with 2 V, 2 mA DC power and 5.8 GHz-band LNA performs 6.9 dB gain, 3.3 dB NF with 3 V, 3 mA DC power.The use of high resistive Si substrate, instead of conventional low resistive Si substrate, enables one to reduce the loss of spiral inductor for on-chip matching circuit by 61% at 1.9 GHz and by 78% at 5.8 GHz, and to improve gain and noise performance of the BJT. These improvements are explained as the reduction of dielectric loss of substrate by referring to equivalent circuit model extraction. The fabricated 1.9 GHz-band on-chip matching LNA performs 13.4 dB gain, 1.9 db NF with 2 V, 2mA d.c. power and 5.8 GHz-band LNA performs 6.9 dB gain, 3.3 dB NF with 3 V, 3 mA d.c, power.

Nonlinear analysis of f/sub 0//2 loop oscillation of high power amplifiers

A novel nonlinear analysis of high power amplifier instability has been developed. This analysis method deals with a loop oscillation and presents the conditions for oscillation under large-signal operation by taking account of a mixing effect of FETs. Applying this analysis method to the high power amplifier instability that an output power decreases at some compression point where an f/sub 0//2-wave is observed, it has been found that this instability is caused by an f/sub 0//2 loop oscillation. In addition, it has been verified by analysis and measurement that the oscillation can be removed by employing an isolation resistor in a closed loop circuit.<<ETX>>

C-X band 14 W power amplifier having flat gain and power response

A 5-10-GHz, 14-W amplifier has been developed. It utilizes a multisectional maximally flat impedance transformer whose length is designed to become a quarter wavelength at the highest frequency of the design band to achieve flat gain and flat power response over a wide bandwidth. Using this transformer, the amplifier has achieved a linear gain of 7+or-1 dB, a 1-dB compressed power of 41.5+or-0.8 dBm, and a power-added efficiency of greater than 25% over 5-10 GHz.<<ETX>>

A UHF-band digital pre-distortion power amplifier using weight divided adaptive algorithm

A look up table (LUT) type adaptive digital pre-distortion (ADPD) using a weight divided adaptive algorithm is presented. In this algorithm, an output signal of the power amplifier (PA) is used as a reference signal. Additionally, reference signal is divided by the coefficient of the LUT, so that the characteristics of the PA, such as temperature dependence, do not have influence on the convergence performances. The proposed algorithm is presented and the convergence condition is derived analytically. From the ADPD simulation, we present that the proposed algorithm is more stable than the conventional normalized least mean square (NLMS) algorithm. The developed UHF-band ADPD power amplifier achieved the intermodulation (IM) distortion of -50dBc and the PA efficiency of 18% at output power of 54.8dBm under an integrated services digital broadcasting for terrestrial television broadcasting (ISDB-T) OFDM signal.