A High Slew-Rate Adaptive Biasing Hybrid Envelope Tracking Supply Modulator for LTE Applications

Abstract

As wireless communication enters smartphone era, more complicated communication technologies are being used to transmit higher data rate. Power amplifier (PA) has to work in back-off region, while this inevitably reduces battery life for cellphones.Various techniques have been reported to increase PA efficiency, such as envelope elimination and restoration (EER) and envelope tracking (ET). However, state of the art ET supply modulators failed to address high efficiency, high slew rate, and accurate tracking concurrently.In this dissertation, a linear-switch mode hybrid ET supply modulator utilizing adaptive biasing and gain enhanced current mirror operational transconductance amplifier (OTA) with class-AB output stage in parallel with a switching regulator is presented. In comparison to a conventional OTA design with similar quiescent current consumption, proposed approach improves positive and negative slew rate from 50 V/µs to 93.4 V/µs and -87 V/µs to -152.5 V/µs respectively, dc gain from 45 dB to 67 dB while consuming same amount of quiescent current. The proposed hybrid supply modulator achieves 83% peak efficiency, power added efficiency (PAE) of 42.3% at 26.2 dBm for a 10 MHz 7.24 dB peak-to-average power ratio (PAPR) LTE signal and improves PAE by 8% at 6 dB back off from 26.2 dBm power amplifier (PA) output power with respect to fixed supply. With a 10 MHz 7.24 dB PAPR QPSK LTE signal the ET PA system achieves adjacent channel leakage ratio (ACLR) of -37.7 dBc and error vector magnitude (EVM) of 4.5% at 26.2 dBm PA output power, while with a 10 MHz 8.15 dB PAPR 64QAM LTE signal the ET PA system achieves ACLR of -35.6 dBc and EVM of 6% at 26 dBm PA output power ii without digital pre-distortion (DPD). The proposed supply modulator core circuit occupies 1.1 mm 2 die area, and is fabricated in a 0.18 µm CMOS technology.iii To My Parents and Family iv ACKNOWLEDGMENTS

A Maximum Efficiency-86% Hybrid Power Modulator for 5G New Radio(NR) Applications

“…To achieve this, changing the level number of the switching converter is a research trend [40]. The method by which the controller controls the switching converters by changing the way that voltage is detected [39,[41][42][43][44] is also the focus of research to improve efficiency. A comparison of the performance of the hybrid power modulator proposed in this work and modulators reported in the literature is shown in Table 1.…”

“…To achieve this, changing the level number of the switching converter is a research trend [40]. The method by which the controller controls the switching converters by changing the way that voltage is detected [39,[41][42][43][44] is also the focus of research to improve efficiency.…”

Efficiency Analysis and Design Considerations of a Hysteretic Current Controlled Parallel Hybrid Envelope Tracking Power Supply

“…Hysteresis h is chosen to be equal to ±7mV. Initially, the linear stage starts [14][15][16][17][18], providing current and when the voltage drop across the exceeds +7mV, the hysteretic controller will turn ON the switching converter. The switching stage starts providing the majority of the load current, as given by (3).…”

Analytical Design Solution for Optimal Matching of Hybrid Continuous Mode Power Amplifiers Suitable for a High-Efficiency Envelope Tracking Operation

“…The overall efficiency of the ET architecture is given by the product of the PA efficiency and EA efficiency. The state-of-the-art wideband EA circuits in the literature demonstrate average efficiency of 70% to 85%, depending on the signal bandwidth and the load impedance [7][8][9][10][11]. Therefore, to achieve more than 50% overall efficiency by considering the statistical probability distribution function (PDF) of the modulated signal, the power added efficiency (PAE) of the RF PA at the power back-off region should necessarily surpass 70%.…”