Jeremy D. Popp

Wideband envelope elimination and restoration power amplifier with high efficiency wideband envelope amplifier for WLAN 802.11g applications

This paper presents the design of a silicon bipolar Class-E wideband envelope elimination and restoration (WBEER) power amplifier with a wideband high efficiency envelope amplifier. The envelope amplifier is composed of a linear op-amp stage and a switch buck converter, which achieves high fidelity and high efficiency amplification of wideband high peak to average (PAR) envelope signals. Experimental results show that the envelope amplifier has a bandwidth of 20MHz and 50-60% efficiency. An overall EER power added efficiency (PAE) of 28% at an output power of 19 dBm was achieved for a WEAN OFDM signal at 2.4 GHz.

Highly Efficient and Linear Class E SiGe Power Amplifier Design

This paper discusses the design of monolithic RF broadband Class E SiGe power amplifiers (PAs) that are highly efficient and linear. Load-pull measurement data on IBM 7HP SiGe power devices have been made at 900MHz and 2.4GHz and monolithic class E PAs have been designed using these devices to achieve highest power-added-efficiency (PAE) at these frequencies. It is found that high PAE can be achieved for monolithic single-stage Class E PAs designed using high-breakdown SiGe transistors at ~65% (900MHz) and ~40% (2.4GHz), respectively, which are roughly ~10% lower than the devices maximum PAE values obtained by load-pull tests under optimal off-chip matching conditions. We have also demonstrated that monolithic SiGe class E PAs can be successfully linearized using an open-loop envelope tracking (ET) technique as their output spectra pass the stringent EDGE transmit mask with margins, achieving overall PAE of 44.4% for the linearized PA system that surpasses the < 30% PAE with commercially available GaAs Class AB PAs for EDGE applications. These promising results indicate the feasibility of realizing true single-chip wireless transceivers with on-chip RF SiGe PAs for spectrally-efficient non-constant-envelope modulation schemes

Design of Highly Efficient Wideband RF Polar Transmitters Using the Envelope-Tracking Technique

This paper discusses the design issues of highly efficient and monolithic wideband RF polar transmitters, especially the ones that use the envelope-tracking (ET) technique. Besides first reviewing the current state-of-the-art polar transmitters in the literature, three focus topics will be discussed: 1) the system-on-a-chip (SoC) design considerations of the monolithic polar transmitter using ET versus EER (envelope elimination and restoration); 2) the design of highly efficient envelope amplifier capable of achieving the high efficiency, current, bandwidth, accuracy and noise specifications required for wideband signals; and 3) the design of high-efficiency monolithic Si-based class E power amplifiers (PAs) suitable for ET-based RF polar transmitters. A design prototype of a polar transmitter using ET and a monolithic SiGe PA that passed the stringent low-band EDGE (Enhanced Data rates for GSM Evolution) transmit mask with 45% overall transmitter system efficiency will be given; the simulated data of the entire polar transmitter system is also compared against the measurement. Further investigations on how to solve the technical challenges to successfully implement linear and high-efficiency ET-based polar transmitter for broadband wireless applications such as WiBro/WiMAX are also discussed.

Fully-integrated highly-efficient RF Class E SiGe power amplifier with an envelope-tracking technique for EDGE applications

This paper reports on the results of a highly efficient monolithically fully-integrated SiGe Class E power amplifier using envelope tracking techniques for EDGE applications. The envelope-tracking (ET) system includes a discrete linear op-amp and a switching power converter. The RF Class E amplifier was fabricated in a 0.18 /spl mu/m BiCMOS SiGe technology. The RF Class E power amplifier achieved a collector efficiency (CE) of 62.7% and the overall power added efficiency (PAE) of the ET system is 44.4% at an output power of 20.4 dBm for an 881 MHz EDGE modulated signal. A discrete envelope switching amplifier achieved 82.8% efficiency while driving the Class E PA voltage supply. The linearized SiGe PA passed the stringent EDGE transmit spectrum mask.

Highly Efficient Monolithic Class E SiGe Power Amplifier Design at 900 and 2400 MHz

This paper discusses the impact of transistor performance and operating frequency on the design of monolithic highly efficient RF SiGe power amplifiers (PAs) using on-chip lump-element passives and/or bondwires to approximate the class E switching conditions. Single-stage SiGe PAs were designed and fabricated using both high-breakdown and high- fT devices targeting for the highest power-added-efficiency (PAE). The PAs designed using high-breakdown devices with on-chip tank inductors exhibit similar gain and PAE as those of high-fT devices, but capable of withstanding significantly higher supply voltages and deliver larger output power (> 23 dBm) more reliably. PAE of 68% (900 MHz) and 40% (2.4 GHz) was achieved from these highly integrated suboptimal PAs without using any off-chip matching. The degraded PAE at 2.4 GHz versus 900 MHz is shown to be caused by increased effective ground inductance parasitics, higher loss from both low-Q on-chip tank inductor and increased SiGe device switching loss with reduced power gain. Design insights on how to improve PAE of SiGe PAs at higher RF frequencies are discussed, as we increased the measured PAE of the class E PAs to an impressive 62-65% range at 2.3-2.4 GHz, which is among the best reported in the literature for Si-based monolithic PAs.

The limitations in applying analytic design equations for optimal class E RF power amplifiers design

The power efficiency of the final stage power amplifier (PA) in a RF transmitter is critical for the overall power consumption, size, lifetime, and reliability of RF transceiver products, especially for portable low-power highly-integrated RF-SoC applications. This paper discusses the limitations and issues in applying the analytic design equations for designing highly efficient RF class E PAs. The main focus of this work is on the validation of the previously published analytic design equations for optimal class E PAs design, as we implemented the PA designs using both discrete RF transistors and monolithic RF ICs at 300 to 2400 MHz. It is found that these analytic design equations available in the literature for RF class E PAs design largely ignored some important physical factors such as the bias sensitivity for the transistor, the undesired device parasitics at RF frequencies, the finite inductance and the low quality factor of the RF choke and/or tank inductors, the time-varying input impedance, and PA stability, etc. They are therefore in general not adequate for predicting the optimal class E PA performance at RF frequencies.

Linearization of Highly-Efficient Monolithic Class E SiGe Power Amplifiers with Envelope-Tracking (ET) and Envelope-Elimination-and-Restoration (EER) at 900MHz

The linearization of highly efficient monolithic SiGe Class E power amplifiers (PAs) using both Envelope-Tracking (ET) and Envelope-Elimination-and-Restoration (EER) techniques has been studied at 900MHz. Without applying any linearization, the fully-integrated SiGe PAs achieve power-added efficiency (PAE) of 66% with no off-chip matching. The overall PAE of an ET-linearized PA system is 45% at an output power of 20dBm for an 881MHz EDGE (Enhanced Data Rate for GSM Evolution) modulated signal. The ET-linearized PAs pass the stringent EDGE transmit spectrum mask, but the EER-linearized PAs do not. The PAE of the ET system is expected to reach ~50% with further efficiency improvement on the envelope amplifier.

Monolithic Class E SiGe Power Amplifier Design with Wideband High-Efficiency and Linearity

This paper discusses and compares the design of monolithic RF broadband class E SiGe power amplifiers (PAs) centered at 900MHz that are highly efficient and linear. It is found that high power-added-efficiency (~65%) can be achieved with PAs designed using either high-breakdown or high-fT SiGe transistors. The PAs designed with high-breakdown devices can provide ~3% better efficiency at higher supply voltages but with worse bias sensitivity, inferior broadband frequency response, and slightly lower gain than those designed with high-fT devices. However, the class E PAs designed using high-breakdown devices can be successfully linearized using an open-loop envelope tracking (ET) technique as their output spectra pass the stringent EDGE transmit mask with margins, achieving an overall system PAE of 44.4% that surpasses the ~30% PAE obtainable using commercial GaAs class AB PAs. These promising results indicate the feasibility of realizing true single-chip wireless transceivers with on-chip RF SiGe PAs for spectrally-efficient non-constant-envelope modulation schemes

Experimental investigations and behavior modeling for monolithic quasi-class E SiGe PA linearization

We have developed a modified bias-dependent Cannpsilas model and performed IC design and hardware experiments to study the linearization of a highly-efficient monolithic quasi-class E SiGe power amplifier (PA) IC using both envelope-tracking (ET) and Envelope-elimination-and-restoration (EER) techniques. Our simple PA behavior model fits the measured SiGe PA IC data very well across a wide range of bias and supply voltages. Both measurement and simulations show that the ET-linearized PA system is significantly less sensitive to the timing misalignment between the amplitude and the RF signal path than the EER-linearized PA system. Our experimental results also show that ET successfully linearized the SiGe PA to pass the stringent EDGE transmit mask at 900 MHz, while EER could not. Simulations also predict that the optimal timing alignment for ET linearization can be achieved at PA base bias voltage Vbb=0.55-0.6 V, which is consistent with our measurement results as well.

Design of highly efficient and linear class E SiGe power amplifier for highly-integrated multifunctional wireless transmitters

This paper discusses the design of highly efficient and monolithic linear RF Class E SiGe power amplifiers (PAs) at both 900 MHz and 2.4 GHz for various wireless applications. Without needing off-chip on-board matching, we achieved very high power-added-efficiency (PAE) for the single-stage Class E SiGe PAs at -70% (900 MHz) and -60% (2.4 GHz), respectively, which performance rivals that of commercially-available III-V PA modules. These switch-mode PAs can be successfully linearized using polar modulation and a hybrid Envelope Tracking (ET) technique, resulting in impressive high PAE suitable for implementing future highly-integrated multifunctional wireless transceivers systems.