In this paper, an accurate experimental noise model to improve the EEHEMT nonlinear model using the Verilog-A language in Agilent ADS is presented for the first time. The present EEHEMT model adopts channel noise to model the noise behavior of pseudomorphic high electron mobility transistor (pHEMT). To enhance the accuracy of the EEHEMT noise model, we add two extra noise sources: gate shot noise and induced gate noise current. Here we demonstrate the power spectral density of the channel noise Sid and gate noise Sig versus gate-source voltage for 0.25 µm pHEMT devices. Additionally, the related noise source parameters, i.e., P, R, and C are presented. Finally, we compare four noise parameters between the simulation and model, and the agreement between the measurement and simulation results shows that this proposed approach is dependable and accurate.

The author developed a wideband precise I/Q modulator using GaAs pHEMT technology. In this technology, pHEMT has 0.22 µm metallurgical gate length and ft=51 GHz at Vds=5V. With the careful design of the wideband phase shifter, this IQ modulator achieved a large wideband frequency range of 250 MHz to 8 GHz and good EVM performance after calibration. For overall frequency range, low distortion performance is obtained, where third order intermodulation is less than -42 dBc. Also the ACPR at 2.2 GHz for W-CDMA application is less than -74 dBc.

Conventional multi-gate pseudomorphic high-electron-mobility transistors (pHEMTs) in the off-state generate larger distortion than single-gate pHEMTs in RF switch applications. To reduce the distortion, the intergate region of multi-gate pHEMTs must be connected to the source and drain with resistors to be biased at the same DC voltage. The intergate region of multi-gate pHEMTs is too small to have an external electrical contact, so intergate-channel-connected pHEMTs (IGCC-pHEMTs) have been developed. IGCC-pHEMTs have a meander gate structure, where one side of the gate is connected to a metal wire layer, and the other is applied for an intergate region contact that does not widen the distance between the gates. A single-pole double-throw (SPDT) switch with IGCC-pHEMTs was fabricated by using a standard 0.5 µm InGaAs pHEMT process. A SPDT switch with IGCC-pHEMTs is confirmed to have almost same small-signal properties and generate lower distortions.

This paper reports the new gate and recess structure design of millimeter-wave, high power pHEMTs, which highly improves humidity resistance and reliability. By using tantalum nitride as the refractory gate metal and a silicon nitride layer prepared by a catalytic chemical vapor deposition technique for passivation of this transistor, strong moisture resistance was obtained without degradation of the device characteristics. Moreover, we have designed a stepped recess structure to increase the on-state breakdown voltage without degradation of the power density of the millimeter-wave pHEMT, according to the analysis based on the new nonlinear drain resistance model. Consequently, the developed pHEMT has shown strong humidity resistance with no degradation of the DC characteristics even after 1000 hours storage at 400 K and 85% humidity, and the high on-state breakdown voltage of over 30 V while keeping the high power density of 0.65 W/mm in the Ka band. In addition, the proposed nonlinear drain resistance model effectively explains this power performance.

The author developed a GaAs wideband IQ modulator IC, which is utilized in RF signal source instruments with direct-conversion architecture. The layout is fully symmetric to obtain a temperature-stable operation. However, the actual temperature drift of EVM (Error Vector Magnitude) is greater in some frequency and temperature ranges than the first generation IC of the same architecture. For applications requiring the precision of electric instrumentation, temperature drift is highly critical. This paper clarifies that linear phase error is the dominant factor causing the temperature drift. It also identifies that such temperature drift of linear phase error is due to equivalent series impedance, especially parasitic capacitance of the phase shifter. This effect is verified by comparing the SSB measurements to a mathematical simulation using an empirical temperature-dependent small-signal FET model.

This paper presents a cascode-pair distributed amplifier design approach using 0.25 µm GaAs-based PHEMT MMIC technology, which covers 2-32 GHz. Electromagnetic simulation results show that this amplifier achieves 18 dB gain from 2 to 32 GHz and 0.5 dB gain flatness over the band. The reflected coefficients at the input and output ports are below -10 dB up to 27 GHz. The output power at 1 dB compression is greater than 24 dBm at 20 GHz. An appropriate feedback resistance can be utilized to improve P1 dB for about 6 dBm. The DOE (design of experiment) approach is carried out by a simulation tool for better performance and tolerance of the devices is also analyzed. The circuit configuration is capable of operating over ultra-broad band amplification.

The parasitic capacitances induced in the spaces between an air-bridge interconnection and a drain pad (Cad), and between an air-bridge interconnection and a gate head (Cag) from a power CPW PHEMT are not negligible. In this paper, a modified equivalent circuit model for a CPW PHEMT and an improved CPW PHEMT for millimeter-wave applications are proposed. These were proved by measuring the fabricated CPW PHEMT and improved CPW PHEMT. These capacitances were confirmed by measuring the gate-source coupling using CPW PHEMT patterns without an active layer. From the measurements, the improved CPW PHEMT has the lowest coupling (loss) and the highest S21 gain among four different types tested at 60 GHz. And the improved CPW PHEMT is a feasible device which can be directly applied in millimeter-waves as a power device.

In this paper, we propose a simple and accurate transfer function model of the power amplifiers for mobile communications. Detail analysis yields a generalized model for AM/AM characteristics in classes AB, B, and C. The analysis includes the effect of drain current variation with input level variation. This model introduces a loadline variation ratio to indicate the change of drain current and to represent the operation classes in a small signal region. Further discussion leads to simplified approximate equations for the AM/AM characteristics, and the estimation procedures for the simplified model parameters. Using the derived procedures, an efficient power amplifier employing pseudomorphic high electron mobility transistor (PHEMT) is fabricated for the 2 GHz band. Finally, the various characteristics given by the model, simulator and measurements are compared and found to agree well in the range of 20 dB below the saturated output level. The model is very effective for characterizing the power amplifiers that are used in linear compensation techniques such as predistortion methods, due to its severe nonlinearity of AM/AM and AM/PM characteristics.

An L-Band high efficiency and low distortion multi-stage amplifier using self phase distortion compensation technique is presented. In this amplifier, the bias condition of the driver-stage transistor is tuned to compensate the phase distortion of the power-stage transistor, and the load and source impedances of the driver-stage and power-stage transistors are optimized to achieve the maximum efficiency with a specified adjacent channel leakage power (ACP) for multi-stage amplifier. The developed amplifier achieves a power added efficiency (Eadd) of 42.8% and an output power (Pout) of 26.8 dBm with an ACP of -38 dBc at 1.95 GHz for wide-band code-division multiple-access (W-CDMA) cellular phones.

A novel InGaAs/InAlAs insulated gate (IG) pseudomorphic high electron mobility transistor (PHEMT) having a silicon interface control layer (Si ICL) is successfully fabricated and characterized. Systematic efforts to characterize and optimize the insulated gate structure and the PHEMT fabrication process were made by using in-situ X-ray photoelectron spectroscopy (XPS) and capacitance-voltage (C-V) techniques. This led to successful fabrication of a novel IG-PHEMT showing excellent stable DC characteristics with a good pinch off and a high transconductance (177 mS/mm), very small gate leakage currents, very high gate breakdown voltages (about 40 V) and respectable RF characteristics fT = 9 GHz and fmax=38 GHz.

Miniaturized millimeter-wave HMIC amplifiers have been developed by using capacitively-coupled matching circuits (CCMC) and FETs with resistive source-stubs. CCMC includes FET's parasitic reactances, and is able to reduce the size of a matching circuit in a HMIC amplifier to about 1/3 of a conventional matching circuit using an open-circuited stub for matching and a quarter-wavelength coupled-line for d. c. blocking. The resistive source-stubs, which consist of two open-circuited stubs and a resistor, can improve the gain and stability of FETs at millimeter-wave frequencies. In this paper, design procedures of CCMC and the resistive source-stubs are described, and their usefulness has been confirmed experimentally through measurements of prototype V-band high-power HMIC amplifiers.