Analyzing the improvement in efficiency through the integration of class-F power amplifiers compared to class-AB in an envelope tracking architecture
This paper investigates the performance of a class-F mode power amplifier (PA) integrated in an envelope tracking (ET) environment, compared to the conventional class-AB mode of operation in the same setting. A 10W high voltage laterally diffused metal oxide semiconductor (HVLDMOS) device is used to perform the comparison at 900MHz using an active load pull system in an emulated ET environment at 900MHz. The analysis looks at three scenario of optimization: when the class-F and class-AB PA's are optimized at individual drain voltage within the ET range, optimized at peak drain voltage, and optimized at the average drain voltage. The challenges of maintaining the device in class-AB and class-F modes throughout the ET range due to the variation of the device output capacitance are also presented in terms of the trajectory of the fundamental and harmonic loads, as well as the degradation in drain efficiency.
An 8 W GaAs Class-AB amplifier for operation in envelope tracking systems
In this paper an 8 W GaAs HEMT power amplifier for operation in envelope tracking systems is presented. The application targeted is UMTS downlink operation with a peak-to-average ratio of about 7 dB. By varying the drain bias voltage between 5 V and 12 V the compression point can be shifted in the required area. Power-added efficiency is more than 45 % in this area and above 52 % in the area of average output power of a UMTS signal. Gain can be kept above 14 dB in this operation mode with a variation of 3 dB.
High Efficiency WCDMA Envelope Tracking Base-Station Amplifier Implemented with GaAs HVHBTs
A high-performance GaAs HVHBT WCDMA/WiMAX base-station power amplifier is presented, which uses an envelope tracking bias system to achieve high linearity and efficiency. The measured overall power-added efficiency (PAE) reached 58%, with a normalized power RMS error of 2.9% and ACLR1 of -49 dBc with digital predistortion (DPD), at an average output power of 42 W and gain of 10.2 dB for a single carrier WCDMA signal at 6.6 dB PAR. To the authors' knowledge, this corresponds to the best efficiency reported for a single stage WCDMA base-station power amplifier. For 7.7 dB PAR single carrier WCDMA overall PAE reached 55%, with a normalized power RMS error of 2.9% and ACLR1 of -48 dBc with DPD, at an average output power of 33 W and gain of 10.2 dB. DPD was used at two levels: memoryless DPD to compensate for the expected gain variation of the amplifier over the bias envelope trajectory, and deterministic memory mitigation, to further improve the linearity. DPD with memory mitigation resulted in -70 dBc ACLR1&2 and 0.3% RMS error, resulting in a best reported linearization improvement result. For 10 MHz WiMAX at 8.8 dB PAR overall PAE reached 48%, with an ACLR1 of -41 dBc with DPD, at an average output power of 25 W and gain of 10.4 dB.