Jerry Lopez

A SiGe Envelope-Tracking Power Amplifier With an Integrated CMOS Envelope Modulator for Mobile WiMAX/3GPP LTE Transmitters

This paper presents a SiGe envelope-tracking (ET) cascode power amplifier (PA) with an integrated CMOS envelope modulator for mobile WiMAX and 3GPP long-term evolution (LTE) transmitters (TXs). The entire ET-based RF PA system delivers the linear output power of 22.3/24.3 dBm with the overall power-added efficiency of 33%/42% at 2.4 GHz for the WiMAX 64 quadrature amplitude modulation (64QAM) and the 3GPP LTE 16 quadrature amplitude modulation, respectively. Additionally, it exhibits a highly efficient broadband characteristic for multiband applications. Compared to the conventional fixed-supply cascode PA, our ET-based cascode PA meets the WiMAX/LTE spectral mask and error vector magnitude spec at close to its P1dB compression without the need of predistortion. The SiGe PA and the CMOS envelope modulator are both designed and fabricated in the TSMC 0.35-μm SiGe BiCMOS process on the same die. This study represents an essential integration step toward achieving a fully monolithic large-signal ET-based TX for wideband wireless applications.

A highly efficient SiGe differential power amplifier using an envelope-tracking technique for 3GPP LTE applications

This paper presents a highly-efficient polar transmitter (TX) system that adopts the envelope-tacking (ET) technique with a differential SiGe power amplifier (PA) for 3GPP Long Term Evolution (LTE) applications. The differential PA was designed using a cascode topology, reaching power-added efficiency (PAE) of 50% at output power of 22dBm in continuous wave (CW) mode. The experimental data also shows that the proposed ET-based polar TX system with the cascode PA delivers 21dBm average output power with 33.6% PAE at 1.42 GHz, while also meeting the LTE 16QAM linearity specs for both error vector magnitude (EVM) and TX emission mask without the need of PA predistortion.

Design of highly-efficient wideband RF polar transmitters using Envelope-Tracking (ET) for mobile WiMAX/Wibro applications

This paper discusses both circuits and system design aspects of highly-efficient wideband RF polar transmitters for mobile WiMAX/Wibro applications using an open-loop envelope tracking (ET) technique. The design of linear-assisted switching envelope amplifier and monolithic SiGe class-E power amplifier (PA) is discussed, while the SPICE simulation results are compared with the measurement data. WiMAX/Wibro circuit and system co-design that include RF circuits and digital DSP blocks co-simulations suggest that the entire highly integrated ET-based transmit (TX) system can meet the stringent 802.16e mobile-WiMAX TX mask with 64QAM modulation and reach ∼33% peak system efficiency.

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.

Design of High Efficiency Monolithic Power Amplifier With Envelope-Tracking and Transistor Resizing for Broadband Wireless Applications

This paper presents the design insights for the implementation of a fully monolithic radio frequency (RF) power amplifier (PA) using both envelope-tracking (ET) and transistor resizing techniques for long-term evolution (LTE) applications. At the low output power region, some of the power cells in the PA can be disabled to further save power consumption, thus enhancing the efficiency from a traditional ET-PA. Our ET-PA system is first realized with a two-chip solution, consisting of a high voltage envelope modulator fabricated in a 0.35 μm Bipolar-CMOS-DMOS (BCD) technology, and a differential cascode PA in a 0.35 μm SiGe BiCMOS technology. This two-chip solution of the ET-PA is to showcase the effective efficiency enhancement of using the transistor resizing method. In the second design, a CMOS envelope modulator is integrated with the cascode PA on the same die in the 0.35 μm SiGe BiCMOS technology. Some insights are demonstrated regarding the optimization of the envelope modulator specific to our cascode PA for LTE broadband signals, where the finite bandwidth and the switching frequency of the envelope modulator are considered for achieving the minimal error-vector magnitude (EVM) and spurious noise. The fully monolithic BiCMOS ET-PA reaches the maximum linear output power (Pout) of 24 dBm and 23.4 dBm with overall power-added-efficiency (PAE) of 41% and 38% for the LTE 16QAM 5 MHz and 10 MHz signals at 1.9 GHz, respectively, without needing predistortion. At the low power mode of our ET-PA, an additional PAE enhancement of 4% is obtained at Pout of 16-20 dBm by disabling some of the PA power cells. Our fully monolithic ET-PA satisfies the LTE 16QAM linearity specs with high efficiency.

High-Efficiency Silicon-Based Envelope-Tracking Power Amplifier Design With Envelope Shaping for Broadband Wireless Applications

This paper presents a highly efficient silicon-based envelope-tracking power amplifier (ET-PA) for broadband wireless applications. A pseudo-differential power amplifier (PA) is designed using two integrated SiGe power cells fabricated in a 0.35- μm SiGe BiCMOS technology with through-silicon-via (TSV). In the continuous-wave (CW) measurement, the PA achieves a saturated output power (POUT) of around 2 W with power-added efficiency (PAE) above 65% across the bandwidth of 0.7-1.0 GHz. To optimize the ET-PA system performance, several envelope shaping methods such as dc shifting, envelope scaling, envelope clipping, and envelope attenuation at back-off have been investigated carefully. A highly efficient monolithic CMOS envelope modulator (EM) integrated circuit (IC) is designed in a 0.35- μm bipolar-CMOS-DMOS (BCD) process to mate with our SiGe PA. With the LTE 16 QAM 5/10/20-MHz input signals, our ET-PA system achieves around 28 dBm linear POUT, passing the stringent LTE linearity specs such as the spectrum emission mask with an average composite system PAE of 42.3%/41.1%/40.2%, respectively. No predistortion is applied in this work.

Circuits and System Design of RF Polar Transmitters Using Envelope-Tracking and SiGe Power Amplifiers for Mobile WiMAX

This paper discusses the circuits and system design methodology of a highly-efficient wideband RF polar transmitter (TX) using the envelope-tracking (ET) technique for mobile WiMAX applications. Monolithic power amplifiers (PAs) are designed and fabricated in IBM 0.18 μm SiGe BiCMOS technology, and a linear-assisted switch-mode envelope amplifier is applied to modulate the PA supply voltage to form the core of the RF polar TX. Nonlinearities caused by bandwidth limitation of the envelope amplifier and timing misalignment have been investigated. When driven by WiMAX 64QAM 8.75 MHz signals, the overall PAE of our ET-based polar TX system reaches 30.5% at 17 dBm average output power, while also meeting the stringent WiMAX linearity specs without using any predistortion. When the decresting algorithm using the soft limiter is applied to the baseband, the overall PAE increases to 33%, at the expense of a higher EVM of 4.9%. Based on measurement results, our ET-based polar TX system has demonstrated excellent efficiency with good linearity for high peak-to-average ratio (PAR) broadband signals when compared with the recent literature on state-of-the-arts polar TX designs.

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.

A Fully Monolithic BiCMOS Envelope-Tracking Power Amplifier With On-Chip Transformer for Broadband Wireless Applications

This letter presents a power-combined BiCMOS power amplifier (PA) system using envelope-tracking (ET) to serve as a fully monolithic solution for high peak-to-average ratio (PAR) broadband signals. The system consists of two cascode unit PAs combined by an on-chip transformer and modulated by a single envelope modulator. Without needing predistortion, the maximum linear output power of 24.6 dBm/23.8 dBm/23.2 dBm can be achieved with overall power-added-efficiency (PAE) of 26%/24%/22.5% for the LTE 16QAM 5 MHz/LTE 16QAM 10 MHz/WiMAX 64QAM 5 MHz signals at 1.9 GHz. The proposed power-combined ET-PA is fabricated in the TSMC 0.35 μm SiGe BiCMOS technology.

Highly Efficient Class E SiGe Power Amplifier Design for Wireless Sensor Network Applications

This paper discusses the design of highly efficient and monolithic medium-power RF class E SiGe power amplifiers (PAs) in IBM 7HP SiGe BiCMOS technology at both 900 MHz and 2.4 GHz for wireless sensor applications. Without needing off-chip on-board matching, we achieved high power-added-efficiency (PAE) for the single-stage class E SiGe PAs at ~70% (900 MHz) and ~60% (2.4 GHz), respectively. Using large number of downbonds at the emitter node of the PA, optimal device sizing and layout, and careful circuit design with bondwire tank inductors, maximum PAE of 62% at 2.4 GHz is obtained, which performance rivals that of commercially-available III-V PA modules. Taking advantages of the higher output power with breakdown robustness and the excellent PAE for SiGe PAs vs. CMOS PAs, one can not only shrink the battery size and therefore sensor volume, but also reduce the number of nodes required in a wireless sensor network to bring down system cost and simplify data fusion. With improved understanding of on-chip PA loss mechanisms, it is likely that we can push these high-efficient SiGe PAs into higher frequencies of operation (say 10 GHz) to utilize smaller antenna size, enabling new and exciting wireless sensor network applications.