Stanley Wu

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.

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.

Efficiency enhancement and linearity trade-offs for cascode vs. common-emitter SiGe power amplifiers in WiMAX polar transmitters

In this paper, a monolithic RF cascode SiGe power amplifier (PA) design capable of enhancing its power-added efficiency (PAE) is demonstrated. Four RF switches are adopted at the bases of the common-emitter transistors, which can be turned on/off in response to the desired output power. Simulations show that by utilizing device size variation, our cascode PA achieves higher gain and PAE compared to conventional fixed-size cascode PA in the low power region; in addition, it also provides more output power and higher average PAE than single-stage common-emitter PAs. We also studied and compared the linearity performance of our cascode PAs vs. single-stage common-emitter PAs in a RF polar TX using an envelope tracking (ET) technique. We found that even through self-biasing for the common-base device can improve the output distortion of cascode PAs, a single-stage common-emitter SiGe PA designed for comparison is still considerably more linear than cascode PAs. Therefore, more careful system linearization design will be critical when the cascode PAs are adopted in RF polar transmitters (TXs), especially for broadband wireless applications such as mobile WiMAX studied here.

SiGe class-E power amplifier with envelope tracking for mobile WiMAX/Wibro applications

In this paper, we report both circuits design and system simulations using highly-efficient monolithic SiGe class-E power amplifier (PA) with an open-loop envelope tracking (ET) technique for mobile WiMAX/Wibro applications. The 1-stage and 2-stage class-E PAs were designed and fabricated in a 0.18µm BiCMOS SiGe technology. The 1-stage class-E PA achieved peak power added efficiency (PAE) of 62% at output power of 21dBm in single-tone measurement. The design of linear-assisted switching envelope amplifier is also discussed, which involves balancing the tradeoff between efficiency and signal fidelity. Detailed co-design system simulations including RF circuits and digital DSP blocks show that our class-E PA can be linearized by the open-loop ET technique, and the entire ET-based transmit (TX) system meets the stringent 802.16e TX mask with ∼33% overall average efficiency at output power of 18.5dBm.

A broadband SiGe power amplifier in an efficient polar transmitter using envelope-tracking for mobile WiMAX

This paper presents a broadband cascode SiGe power amplifier (PA) in the polar transmitter (TX) system using the envelope-tacking (ET) technique. The cascode PA achieves the power-added efficiency (PAE) of >30% across the frequency range of 0.6∼2.4 GHz in continuous wave (CW) mode. The ET-based polar TX system using this cascode PA is evaluated and compared with the conventional stand-alone cascode PA. The experimental data shows that the cascode PA is successfully linearized by the ET scheme, passing the stringent WiMAX spectral mask and the required error vector magnitude (EVM). The entire polar TX system reaches the PAE of 30%/36% at the average output power of 18/17 dBm at 2.3/0.7 GHz for WiMAX 16QAM 3.5 MHz signals. These measurement results suggest that our saturated cascode SiGe PA can be attractive for dual-mode WiMAX applications.

A de-cresting technique for polar transmitters using Envelope-Tracking (ET) and SiGe power amplifiers for mobile-WiMAX

A decresting algorithm for mobile WiMAX has been developed using time domain clipping and filtering processes for a polar transmitter (TX) using Envelope-Tracking (ET) and a monolithic SiGe power amplifier (PA). RF/Analog/Digital system and circuits co-design simulations have been performed for mobile WiMAX with 64 QAM OFDM modulation format. It is found that higher power-to-average ratio (PAR) decresting can improve the adjacent channel power ratio (ACPR) and the overall TX system efficiency, but at the cost of its EVM degradation. Our system simulations show that careful design of signal decresting can improve the overall polar TX system efficiency from 28.1% to 30.3% while the TX output can still meet the stringent WiMAX TX mask and EVM specs.

An ultra-low power interface CMOS IC design for biosensor applications

This paper presents a design example of an ultra-low power single-channel analog front-end (AFE) integrated circuits (IC) and system for biomedical sensing applications. The 0.18-μm CMOS AFE IC design includes a low noise instrumentation amplifier (INA), a low-pass filter (LPF), a variable gain amplifier (VGA), and a successive approximation register (SAR) analog-to-digital converter (ADC). The AFE IC architecture is analyzed on the system level to minimize total power consumption with high integration and optimized for an ECG sensing system. SPICE simulations of the AFE IC channel validate the ultra-low power IC design methodology for heartbeat detection with less than 1 μA/channel.

A highly-efficient RF polar transmitter using SiGe power amplifier and CMOS envelope-tracking amplifier for mobile WiMAX

This paper presents a large-signal envelope-tracking (ET) polar transmitter (TX) system with a monolithic cascode SiGe power amplifier (PA) for mobile WiMAX applications. The envelope amplifiers are designed in the TSMC 0.35µm SiGe BiCMOS technology and also with discrete components for comparisons. The entire polar TX system using the discrete envelope amplifier in measurement achieves the power-added efficiency (PAE) of 30% at the average output power of 18 dBm with the EVM of 5% for WiMAX 64QAM 10 MHz signal. The RF/analog/digital co-simulations of the entire polar TX system with the integrated CMOS envelope amplifier show similar linearity and efficiency performances when compared with the measurement results. Both the simulation and measurement data suggests our polar TX design achieves the highest PAE among the state-of-the-art Si-based OFDM polar TX systems reported in the literature.