Serguei Chevtchenko

Robust stacked GaN-based low-noise amplifier MMIC for receiver applications

A robust two-stage low-noise amplifier based on GaN technology is presented. The MMIC LNA is realized using stacked transistors in the first stage to obtain high ruggedness. The LNA survived a record value of 43 dBm of input power at 5 GHz measured in a coaxial test fixture without any visible degradation of the transistors. The results prove that the new stacked architecture allows the LNA to withstand twice the CW input power expected for the conventional topology.

A flexible GaN MMIC enabling digital power amplifiers for the future wireless infrastructure

This paper presents a GaN power-switch MMIC and demonstrates its potential and its versatility in realizing power amplifier (PA) modules for future LTE base station transmitters with an increased digital content. The MMIC provides a compact high-gain broadband voltage-mode PA. With a TTL-level input voltage swing of 0.4 Vpp it reaches a large-signal gain of up to 40 dB. The PA can be used as a building block for various class-S and related applications. As examples, a single-chip and an H-bridge PA module for the 800 MHz band are reported as well as a digital Doherty PA.

A dual-band voltage-mode class-D PA for 0.8/1.8 GHz applications

This paper presents a compact dual-band voltage-mode class-D power amplifier module suitable for the LTE frequency bands at 0.8 GHz and 1.8 GHz. It uses a broadband GaN voltage-mode PA MMIC and a hybrid lumped element dual-band filter structure. The amplifier can handle various pulse-mode or digital modulation schemes. For a pulse-width modulated input signal the PA achieves a maximum output power of 5.4 W at 0.85 GHz and 4.3 W at 1.8 GHz. Peak drain efficiency is 84% and 54% for 0.85 GHz and 1.8 GHz, respectively. At 6 dB power back-off, drain efficiencies of 40% (0.85 GHz) and 25% (1.8 GHz) are obtained.

Highly linear X-band GaN-based low-noise amplifier

This paper presents a highly linear X-Band low-noise amplifier. The LNA is realized in coplanar technology using the 0.25 μm GaN-HEMT MMIC process from FBH. A noise figure below 2.5 dB is measured from 7 GHz to 12 GHz together with very good input and output matching. This LNA provides a OIP3 of 28 dBm at 8 GHz, which is 8 dB above the 1 dB compression point.

Terahertz rectification by plasmons and hot carriers in gated 2D electron gases

Here we discuss on detection using antenna-coupled field effect transistors. We show, that gate-to-channel separation plays strong role for the dispersion of plasmons excited within the channel changing from gated 2D to ungated 2D plasmon. This change also strongly affects the impedance and the efficiency of rectification. We present experimental data which clearly indicates on with plasmonic rectification competing physical phenomenon. There are strong indications, that this additional signal originates from the inhomogeneous heating of charge carriers i.e., diffusion of “warm” electrons.

Potential of Coplanar X-band GaN-MMIC Power Amplifiers

Abstract While the vast majority of GaN X-band PAs is realized as microstrip circuits, this paper reports design, fabrication and measurement of a coplanar version. The amplifier is processed using the FBH 4-inch GaN-on-SiC technology with 0.25 µm-gate GaN HEMTs. The two-stage power amplifier circuit delivers more than 12 W cw output power at 10 GHz, with a large-signal gain of 20 dB and a final stage drain efficiency of 45%. Benchmarking shows that these are best-in-class values for a coplanar X-band MMIC, which come very close to the state-of-the-art microstrip counterparts.

RF-power GaN transistors with tunable BST pre-matching

A thick-film Barium-Strontium-Titanate (BST) varactor is evaluated as gate pre-matching element for integration in discrete RF-power GaN-HEMTs. The tunable pre-matching is connected to the gate of a 2 mm GaN cell and characterized by load-pull measurements in the 2 to 3 GHz range. The assembly shows large tunable impedance range with low impact on power performance. At 2.0 GHz gain is reduced by 3.6 dB to 20 dB. The saturated output power at more than 37.8 dBm and the linearity are unaffected.

Efficient detection of short-pulse THz radiation with field effect transistors

Here we report on the efficient detection of THz radiation generated from Ti:sapphire femtosecond laser system. The large-area interdigitated antenna is excited by optical pulses with pulse duration from 15 to 47 fs. We have tested two AlGaN/GaN HEMT-based THz detectors with integrated broadband antennas. Detectors are comparable in sensitivity but differ in applied parasitic signals elimination techniques. Despite being sensitive, the pick-up of the first detector without strong parasitic elimination exceeded the theoretically expected noise level about 100 times. For a second detector we have implemented more stringent interference avoiding techniques, such as gate shunting with a low resistance value resistor, and have managed to significantly improve systems detection capabilities. We have lowered a pick-up near to the thermal noise level and have extended signal/noise ratio to 26 dB.

Noise in GaN HEMTs and circuits

GaN HEMTs are known to outperform GaAs technologies in power applications, while their noise performance drew much less attention. Only recently, results were published for GaN that are competitive in terms of low-noise performance. This paper discusses the optimization of GaN HEMT technology concerning low-noise performance empirically, based on own measurements and on data from the literature. Finally, the current status in low-noise amplifier performance and ruggedness is briefly discussed.

Optimization of the Design of Terahertz Detectors Based on Si CMOS and AlGaN/GaN Field-Effect Transistors

TeraFETs are THz power detectors based on field-effect transistors (FETs) integrated with antennas. The first part of this paper discusses the design of Si CMOS TeraFETs leading to an optimized noise-equivalent power close to the room-temperature limit. The impact of the choice of the gate width and gate length, the role of the parasitic effects associated with the technology node, and the conjugate matching of antenna and FET impedance – which is possible over narrow THz frequency bands because of the frequency dependence of the channel impedance resulting from plasmonic effects – are highlighted. Taking these aspects into account, we implement narrow-band detectors of two different designs. Using a 90-nm and a 65-nm CMOS technology, we reach a room-temperature cross-sectional NEP of 10 pW/√Hz at 0.63 THz. We then explore the optimization of AlGaN/GaN TeraFETs equipped with broadband antennae. A room-temperature optical NEP of 26 pW/√Hz is achieved around 0.5 THz despite the fact that the existence of pr...