Sebastian Preis

Investigation of class-B/J continuous modes in broadband GaN power amplifiers

The class-B/J mode continuum in power amplifiers (PAs) defined at the current source plane is discussed considering different parasitic elements including CDS as well as the package. Based on this realistic device description the change of the continuous load impedances depending on the reference plane is demonstrated. It is shown that the design flexibility predicted by the continuous mode theory decreases if the transistor package is taken into account. The presented investigations provide the basis for the design of a broadband GaN PA. In the frequency range of 0.9 GHz to 1.8 GHz, this PA achieves a saturated output power of more than 70 W with an efficiency η of 56–63 %. In the extended frequency band up to 2.3 GHz an output power of still 60 W with 53 % drain efficiency is available.

Iterative design of a harmonically tuned multi-octave broadband power amplifier

This article presents the design approach, realization and measurement results of a highly efficient double octave wideband power amplifier using a GaN-HEMT bare-die. An iterative approach to obtain the optimum source and load impedances is described. Multiple harmonics are analyzed using harmonic load-pull simulation and a reliable large-signal device model. The design was realized exploiting a transition between two substrates and a vertical impedance step transformation. From 1.5 GHz to 6 GHz, a constant high output power and remarkable efficiency were achieved. More than 20 W saturated power and 50 % drain efficiency were measured up to 5.5 GHz.

Highly efficient and wideband harmonically tuned GaN-HEMT power amplifier

In this paper, the design of a highly efficient 25 W GaN-HEMT power amplifier (PA), operating in 1.7 - 2.3 GHz, is presented. The influence of the harmonics and the impact of the parasitic components of the nonlinear device are considered in order to ensure an accurate matching network design to achieve high efficiency. Optimum fundamental and harmonic load impedances were obtained using load-pull simulations across the operation band. From continuous wave large-signal measurements, an average output power of 44 dBm was obtained over the bandwidth. The corresponding drain efficiency ranged between 73 - 80 % with a gain of 12 dB. Linearized modulated measurement, using 10 MHz LTE signal with 7.3 dB peak-to-average-power-ratio (PAPR), shows an average power-added-efficiency (PAE) of 38.2 % and adjacent channel leakage ratio (ACLR) of almost -45 dBc at 1.8 GHz.

100 W highly efficient octave bandwidth GaN-HEMT power amplifier

In this contribution, the design, implementation, and experimental results of a high-efficiency broadband GaN HEMT power amplifier are presented. Optimum fundamental and harmonic load impedances were obtained using load-pull simulations for the active device across the design bandwidth. A systematic approach was applied for the design of wideband output and input matching networks. Continuous wave (CW) large-signal measurement results showed that across 1.1-2.0 GHz (58 % bandwidth), the output power was higher than 110 W, and 50-72% drain efficiency was achieved. Over the octave bandwidth of 1.0-2.0 GHz, at least 84 W output power was measured. The power gain was around 12 dB. An ACLR of -45 dBc was measured for an LTE signal at 42 dBm average output power under additional digital predistortion (DPD).

VSWR protection of power amplifiers using BST components

A VSWR-protected ISM-band PA was realized using a BST based varactor for detuning of the input matching. Output VSWR levels of 30:1 can be tolerated by applying a varactor bias voltage of up to 20 V. The PA delivers 47.4 dBm output power at a maximum PAE of 49.5%. In case of high VSWR conditions the output power can be limited by detuning the varactor. It is shown that the concept protects the transistor efficiently with very low additional circuit complexity.

Reference Plane Transformation of Continuous Mode Terminations for Broadband Power Amplifiers

Abstract In this article the behavior of continuous mode amplifiers at different reference planes is discussed using the example of a continuous class-F−1 amplifier mode. The variation of the output impedances and the conversion of the output voltage and current waveforms are analyzed depending on the considered reference plane. For instance, the frequently discussed current source reference plane has a way different impedance characteristic than the accessible lead reference plane. In order to study this aspect, a broadband continuous class-F−1 mode amplifier has been realized using a bare-die GaN-HEMT. From 1.0 to 1.8 GHz, this amplifier attains 44.5–45.2 dBm output power with corresponding drain efficiency of 65–68%.

Wideband tunable GaN HEMT module utilizing thin-film BST varactors for efficiency optimization

This work covers the design and measurement of a low cost tunable impedance matching network (TMN) for highly linear and high power RF applications at telecommunication frequencies. A single transistor cell, was wire-bonded to a TMN and the performance of the tunable amplifier module was evaluated from 1 GHz to 2.5 GHz. The TMN transforms the GaN HEMT output impedance to fixed 50 Ohm load. Tuning allows efficient operation of the transistor over the targeted frequency range. Peak drain efficiency of 66% and a peak output power of 37.5 dBm were measured. Two-tone measurements reveal an OIP3 around 47 dBm which is comparable to a bare GaN HEMT.

Wideband 80 W balanced power amplifier for ISM and LTE-bands

An 80 W balanced GaN-HEMT power amplifier for 2.45-2.70 GHz using branch-line couplers is presented in this paper. Its performance is compared to a single-transistor solution. The analysis shows that a balanced amplifier is favorable because it simplifies measures to ensure electrical stability and allows better heat sinking.

Linearity analysis of class-B/J continuous mode power amplifiers using modulated wideband signals

Linearity, along with efficiency and bandwidth, belongs to the fundamental requirements of power amplifiers for nowadays communications systems. This paper discusses how to bring together these partly contradictory goals in power amplifier design. Continuous class-J PAs provide a constant efficiency over a large bandwidth. However, the linearity is not constant due to the unequal current and voltage waveforms along the design space of the continuum. Nevertheless, it is possible to equalize linearity of such a PA over the desired bandwidth. For the PA presented, -50 dBc ACLR with an average power of 38 dBm and an average efficiency of 21.5 % were achieved at 2.14 GHz using a WCDMA test signal. For CW measurements, 48.5 dBm maximum power and 63 % peak drain-efficiency were reached.

Thick-film MIM BST varactors for GaN power amplifiers with discrete dynamic load modulation

Due to their extremely low static current consumption, varactors based on BST are perfect devices for realization of tunable and re-configurable components. This work presents fully screen-printed MIM thick-film BST varactors that are used to tune the load impedance for GaN HEMTs. The varactor tuning voltage is supplied in discrete steps using a high-speed GaN-based modulator. Modulated measurements with LTE and WCDMA signals show, for the first time, the functionality of a BST-based load modulation system and the power consumption of the load-modulation in dynamic operation. Using discrete dynamic load modulation, an average PAE of 27.3% was measured for the LTE signal with an ACLR below −45 dB.