Chien-Jung Li

High-performance frequency-hopping transmitters using two-point delta-sigma modulation

This paper presents a 2.4-GHz high-performance frequency-hopping (FH) transmitter using two-point delta-sigma modulation (TPDSM). Two bottleneck problems in the implementation have been studied rigorously. One is the nonlinear performance of a phase-locked loop (PLL). The other is the inherent gain and delay mismatches between two modulation points. Both nonlinear and mismatch factors dominate the modulation accuracy in the closed PLL. Our formulation can predict the dependencies of modulation accuracy on both factors quite successfully. Comparison of the averaged frequency deviation and frequency-shift-keying (FSK) error between theory and measurement shows excellent agreement. The implemented TPDSM-based FH Gaussian FSK transmitter can achieve 2.5-Mb/s data rate along with 15-/spl mu/s PLL stable time with only 2.2% FSK error under good design and operating conditions.

A Novel Vital-Sign Sensor Based on a Self-Injection-Locked Oscillator

A novel vital-sign sensor with a self-injection-locked oscillator and a frequency demodulator to reduce system complexity and improve sensitivity is proposed. The theory provides a delta-sigma model to account for the excellent signal-to-noise spectral density ratio in a parametric study of the sensitivity performance. Then, the experiments verify the sensing principle and the predicted performance. Accordingly, a prototype sensor with high sensitivity is realized for noncontact cardiopulmonary monitoring, achieving a long sensing distance without the need for a low-noise amplifier. The sensing distance can grow four times longer by doubling the operating frequency. Furthermore, the sensor using a swept frequency can eliminate the null detection points and the external radio interference. As an experimental result, the sensor, which is placed 4 m away from the subject, can reliably detect the heartbeat signal an the operating frequency of 3.6 GHz and an output power level of 0 dBm.

Design and Linearization of Class-E Power Amplifier for Nonconstant Envelope Modulation

This paper presents design and linearization techniques for a highly efficient, but nonlinear Class-E power amplifier (PA) applied to linear RF transmitters. To achieve maximum efficiency for Class-E PA operating above gigahertz frequencies, the proposed design theory modifies the classic Class-E condition and considers switch-on and switch-off resistances in deriving the analytical solution. For linearization, a digital envelope predistorter (DEP) is used to provide predistorted envelope modulation for the RF-input and supply-voltage signals fed to the Class-E PA. This DEP can successfully compensate for AM/AM and AM/PM distortions such that the Class-E PA, although classified as a switching-mode PA, can act as a linear PA. A cdma2000 1 times transmitter incorporating this Class-E PA and DEP is demonstrated to simultaneously achieve high efficiency and high modulation quality.

A Rigorous Analysis of a Phase-Locked Oscillator Under Injection

This study presents injection-pulling effects on a local oscillator (LO) for wireless applications. A discrete-time analysis is provided to predict output spectra of the LO pulled by a sinusoidal and angle-modulated injection signal. A phase-locked loop synthesizer with an injection signal is analyzed in frequency domain to account for the inherent bandpass filtering on the injection signal. In addition, a phase noise model is developed by using the proposed frequency-domain approach to characterize the overall phase noise of a phase-locked oscillator under injection. Comparison between theoretical predictions and experimental results shows excellent agreement.

An injection-locked detector for concurrent spectrum and vital sign sensing

This paper proposes a concurrent spectrum and vital sign sensor using an injection-locked detector. To achieve this goal, two different sensing mechanisms are involved. One is to employ the injection locking and pulling effects in an oscillator to fast detect the frequency and power of a wireless communication signal. The other is to use a self-injection-locked oscillator to detect Doppler shift for measuring the breathing and heartbeat rate of a target. A prototype system operating in S-band has been implemented to validate the proposed sensor architecture.

A Novel RF Sensing Circuit Using Injection Locking and Frequency Demodulation for Cognitive Radio Applications

A novel RF sensing circuit for a cognitive radio to sense spectral environment is proposed using injection locking and frequency demodulation techniques. The research starts with deriving a generalized locking equation for oscillators as a theoretical basis, and then develops the sensing principle and circuit architecture to a practical and useful level. To accurately evaluate the sensing performance, a discrete time approach is investigated to compute the sensed output signal. In the experiments, a prototype circuit is designed in the 2.4-GHz industrial-scientific-medical band to cover a sensing frequency range from 2.4 to 2.484 GHz. The spectrum scanning over the 84-MHz bandwidth is accomplished in less than 1 ms. The experimental results agree quite well with the theoretical predictions, showing that the proposed RF sensing circuit can fast and reliably detect frequency and power for analog and digital modulation signals.

Analysis and Improvement of Direct-Conversion Transmitter Pulling Effects in Constant Envelope Modulation Systems

Elucidating how local oscillator (LO) pulling affects a wireless direct-conversion transmitter that uses constant envelope modulation is of concern for global system for mobile communication (GSM). Therefore, this paper presents a phase dynamic model for a phase-locked loop (PLL) under directly modulated self-injection to evaluate the degraded phase noise performance of an LO pulled by a feedback modulation signal from the power amplifier output. Additionally, based on theoretical analysis, the proposed model can instruct system designers on how to optimize PLL parameters, as well as introduce an inner self-injection to minimize the impact of pulling effects. The improved performance is verified by implementing a Gaussian minimum-shift keying transmitter for GSM applications. Furthermore, the theoretical and experimental results correlate well with each other.

High efficiency dual-mode RF transmitter using envelope-tracking dual-band Class-E power amplifier for W-CDMA/WiMAX systems

This paper presents design and linearization techniques for a highly efficient but nonlinear Class-E power amplifier (PA) applied to a dual-mode RF transmitter for W0CDMA/WiMAX systems. At first, a Class-E PA design is carried out for dual-band operation based on the proposed modified Class-E condition. Then, the envelope tracking and digital predistortion techniques are applied to linearize the Class-E PA by improving the PA AM/AM and AM/PM distortions. Consequently, the designed Class-E PA, although classified as a switching-mode PA, can act as a linear PA for diverse high peak-to-average-power-ratio (PAPR) wireless systems. The experimental results show that a quadrature modulation transmitter incorporating the presented envelope-tracking dual-band Class-E PA can simultaneously achieve high average efficiency and adjacent channel power rejection for 1.95 GHz W-CDMA and 2.6 GHz WiMAX applications.

System Design Issues in a HQPM-Based Transmitter

This paper presents the analysis of signal quality and the efficiency performance in an RF transmitter using hybrid quadrature polar modulation (HQPM) scheme. The measurement results of the Class-ii power amplifier and Class-5 modulator are applied in this analysis. The path-delay difference between the envelope and the phase signal is also considered. Output spectra with and without predistortion are both shown to demonstrate improvement from the predistortion function. The simulated and experimental results have validated the key feature of the HQPM architecture, that its adjacent channel power ratio and DC-to-RF efficiency are not sensitive to the output power level.

A rigorous analysis of local oscillator pulling in frequency and discrete-time domain

This study presents injection pulling effects on a local oscillator (LO) for wireless applications. A phase-locked loop under injection is analyzed in frequency domain to account for the inherent band-pass filtering on an injection signal. A discrete-time analysis is also provided to predict output spectra of the LO pulled by a sinusoidal and modulated injection signal. Comparison between theoretical predictions and experimental results shows excellent agreement.