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.
Comparing FET Technologies in Terms of Their Suitability for Broadband Envelope Tracking Power Amplifiers
Envelope tracking power amplifiers (ET PAs) are one of the main contenders for future communication systems. Their operation over a wide range of supply voltages ($V_{\text{D}})$ leads to an extended set of requirements, this paper investigates a number of technologies, including Si LDMOS, GaAs pHEMT and GaN HEMT and how they behave in broadband ET PAs. The increased impact of the feedback capacitance $C_{\text{GD}}$ on broadband PA design in HEMT devices caused by a reduced $V_{\text{D}}$ is described for the first time. Analysis of the $V_{\text{D}}$ dependent characteristics show that GaN HEMTs can exhibit the most promising behaviour for broadband ET PAs due to their favourable output voltage dependent gain variationand their low capacitance to power ratio, so long as field plate designs are used to guarantee a favourable knee walkout.
Optimized Envelope Shaping for Hybrid EER Transmitter of Mobile WiMAX— Optimized ET Operation
The envelope signal of a Hybrid Envelope Elimination and Restoration (H-EER) technique is optimally reshaped to improve linearity and efficiency, resulting in an Envelope Tracking (ET) architecture. The bias Vds of the ET is adjusted to be a higher value than that of the conventional H-EER technique to enhance the output power and power-added efficiency (PAE). Furthermore, the bias is shifted above the knee region of the PA to reduce the AM/AM and AM/PM distortions at the low bias region. For the verification, the Mobile WiMAX signal with 8.2 dB peak-to-average power ratio and 5-MHz signal bandwidth is used. In the interlock experiment, the PAE of the transmitter is 40% at an output power of 42.04 dBm. By using the digital predistortion technique, the Relative Constellation Error has satisfied the specification of - 33.6 dB. These results clearly show that the H-EER transmitter with ET shaping is the most suitable architecture for the highly linear and efficient Base Transceiver Station transmitter.