John Hoversten

Codesign of PA, Supply, and Signal Processing for Linear Supply-Modulated RF Transmitters

This paper presents a method for achieving high-efficiency linear transmitters by codesign of the RF power amplifier (PA), dynamic supply, and signal processing. For varying amplitude signals, the average efficiency of the PA is improved by adding a supply modulator with requirements derived from nonstandard PA modeling. The efficient PA and supply modulator both introduce signal distortion. A targeted linearization procedure is demonstrated with reduced complexity compared to standard digital predistortion. Experimental results on a 2.14-GHz 81% efficient 40-W peak power GaN PA illustrate the codesign method by achieving 52.5% composite power-added efficiency with high linearity for a W-CDMA signal with a 23-MHz supply modulator bandwidth.

Harmonic load pull of high-power microwave devices using fundamental-only load pull tuners

This paper presents a high-power high-efficiency PA design method using traditional fundamental-frequency load pull tuners. Harmonic impedance control at the virtual drain is accomplished through the use of tunable pre-matching circuits and full-wave FEM modeling of package parasitics. A 10-mm gate periphery GaN transistor from TriQuint is characterized using the method, and load-pull contours are presented illustrating the dramatic impact of varying 2nd harmonic termination. A 3rd harmonic termination is added to satisfy conditions for class-F-1 load pull, resulting in an 8% efficiency improvement over the best-case 2nd harmonic termination. The method is verified by design and measurement of a 36-W class-F-1 PA prototype at 2.14GHz with 81% drain efficiency and 14.5 dB gain (78% PAE) in pulsed operation.

Envelope tracking transmitter system analysis method

A general envelope tracking (ET) transmitter is described which utilizes both drive and drain modulation. We develop a simulation method useful for modeling the impact of component non-idealities on system performance, starting from hardware measurement data. An example analysis evaluates tradeoffs between ET system linearity, power amplifier efficiency, and envelope modulator requirements for a W-CDMA down-link transmitter.

A 65-W high-efficiency UHF GaN power amplifier

This paper presents a high-efficiency UHF power amplifier (PA) using a GaN HEMT on a SiC substrate transistor as the active device. The PA delivers 65W with 82% power added efficiency (PAE), and 45W with 84% PAE at 370MHz, with supply voltages of 35V and 28 V, respectively. Load pull techniques under Class-E conditions are used for device characterization and matching network design. The PA is implemented in a hybrid circuit with mixed lumped-element and transmission-line matching networks. A weighted Euclidean distance is defined to enable tradeoff studies between output power (POUT) and efficiency, in order to find the final optimal amplifier design.

Linearity of X-band Class-E Power Amplifiers in a Digital Polar Transmitter

This paper discusses the linearity of a class-E X-band PA in a digital polar transmitter. The PA is nonlinear since it is compressed by 2.2 dB when achieving a 59% PAE at 10 GHz. Load-pull is performed under a two-tone test and the resulting optimal efficiency impedance is found to be over 30% different from the single-tone load-pull. In addition standard two-tone load-pull measurements indicate that the impedance for max Pout coincide with worst nonlinearity (IMD). Surprisingly, in the two-tone polar load-pull, impedance for max Pout differs significantly from the impedance corresponding to worst IMD. Therefore, under polar modulation a different matching circuit should be designed for optimal linearity and efficiency. The PA is part of a digital polar transmitter which enables linearization including phase predistortion, with IMD levels over 11 dB lower than in the standard two-tone test. Load-pull performed on the polar class-E PA shows that the level of intermodulation products varies for different signals input into the PA.