Andreas Wentzel

Fast-Switching GaN-Based Lateral Power Schottky Barrier Diodes With Low Onset Voltage and Strong Reverse Blocking

GaN-based heterostructure lateral Schottky barrier diodes (SBDs) grown on n-SiC substrate are investigated in this letter. These SBDs own very low onset voltage VF = 0.43 V, high reverse blocking VBR >; 1000 V, very low capacitive charge of 0.213 nC/A, and a very fast recovery time of 10 ps. These unique qualities are achieved by combining lateral topology, GaN:C back-barrier epitaxial structure, fully recessed Schottky anode (φB = 0.43 eV), and slanted anode field plate in a robust and innovative process. Diode operation at elevated temperature up to 200 °C was also characterized.

RF class-S power amplifiers: State-of-the-art results and potential

This paper reports recent results on a current-mode class-S power amplifier for the 450 MHz band, based on GaN-HEMT MMICs. We achieve a peak output power of 8.7 W for a single tone at 420 MHz, encoded in standard band-pass delta-sigma modulation with 1.68 Gbps sampling frequency. The respective efficiency is 34%. We find that these values strongly vary with coding efficiency of the modulation and reach 19 W with 59% for square-wave excitation. In order to clarify the potential of the PA in more detail, the S-class characteristics at power back-off and with varying oversampling ratio are presented as well.

Switch-mode amplifier ICs with over 90% efficiency for Class-S PAs using GaAs-HBTs and GaN-HEMTs

This paper reports on design and realization of monolithic switch-mode amplifiers for data rates up to 1.8 Gbps, suitable for Class-S and inverse class-D PA modules. GaN HEMT as well as high-voltage GaAs-HBT technologies are employed and compared. For digital signal transmission without output filtering, the chips achieve efficiencies of more than 90 % at an output power of 5.4 W and 6.5 W with PAE values including the on-chip drivers, of 75% and 80% for GaAs-HBT and GaN-HEMT Ics respectively. These high efficiencies values are very promising since such PA chips represent the key building block for future class S systems.

An 8W GaN-based H-bridge class-D PA for the 900 MHz band enabling ternary coding

This paper presents an H-bridge class-D power amplifier (PA) for the 900 MHz band based on GaN MMICs. For a classical BPDS modulated signal, a maximum output power of 34.5 dBm with a drain efficiency of 22% is obtained. Using a periodic square-wave input signal, the PA achieves a peak output power of 39 dBm and maximum drain efficiency of 48%. Investigating different binary and a ternary coding schemes, up to 30% drain efficiency at 6 dB power back-off is achieved.

A voltage-mode class-S power amplifier for the 450 MHz band

This paper reports on a novel voltage-mode class-S power amplifier for the 450 MHz band, based on GaN-HEMT MMICs. It achieves a peak output power of 3.4 W for a single tone at 400 MHz, encoded in standard band-pass delta-sigma modulation with 1.6 Gbps sampling frequency. The corresponding efficiency is 38%, peaking at 52% for 0.5 W output power. In order to demonstrate the influence of coding efficiency, additional measurements using a periodic square-wave signal were performed (class-D operation), which yield a maximum output power of 6.5 W with 64% efficiency. To the authors knowledge, these are the best results in this frequency range achieved so far with the voltage-mode class-S configuration.

Design and Realization of an Output Network for a GaN-HEMT Current-Mode Class-S Power Amplifier at 450MHz

This paper describes the design and realization of a hybrid lumped output network for a current-mode class-S power amplifier. It consist of a band pass filter, a balun and a broad-band constant current supply. The filter achieves a bandwidth of 300 MHz and 0.5 dB insertion loss. As a demonstrator for the class-S concept, the developed network together with a GaN MMIC switching stage and GaAs Schottky-diodes demonstrates a complete class-S power amplifier for a data rate of 1.8 Gbps for an analog signal frequency of 450 MHz. An output power of 2.7 W at 450 MHz with an efficiency of 19 % and a very high power gain of 37 dB has been achieved. This is the first demonstration of class-S operation at these power levels for this frequency range.

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.

Digital doherty transmitter with envelope ΔΣ modulated class-D GaN power amplifier for 800 MHz band

This paper presents a novel transmitter (Tx) architecture combining voltage-mode class-D power amplifiers (PAs) with an efficient 1-bit envelope delta-sigma modulation scheme for the 800 MHz band. By digitally processing the input 1-bit codes, the proposed Tx operates as a digital Doherty Tx. The proposed Tx architecture is realized with a GaN H-bridge class-D PA module and CMOS modulator ICs and delivers a CW power of 35.9 dBm at 860 MHz with a final-stage drain efficiency of 75.6% at the saturation point. The drain efficiency at 6-dB BO is still 73.4% which corresponds to an improvement of 23.9 points compared to balanced operation. Using a CDMA signal of 1-MHz bandwidth and 6.5-dB peak-to-average power ratio, the digital Doherty Tx achieves an average output power of 28.6 dBm with a drain efficiency of 56.5%.

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.

A Watt-Class Digital Transmitter with a Voltage-Mode Class-S Power Amplifier and an Envelope Delta-Sigma Modulator for 450 MHz Band

A single-bit high efficiency watt-class digital transmitter for the 450 MHz band is presented, using a GaN voltage-mode class-S power amplifier and a CMOS envelope ΔΣ modulator. The transmitter achieves 1.1 W output power with 69% drain efficiency for a 400 MHz WCDMA uplink signal, thus meeting the 3GPP specifications for ACLR. A power control from 0.45 W to 1.8 W is achieved by changing the supply voltage of the power amplifier from 20 V to 40 V, keeping the drain efficiency beyond 58% without any degradation of ACLR.