Chieh-Hsun Hsiao

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.

Cognitive Polar Receiver Using Two Injection-Locked Oscillator Stages

A novel cognitive polar receiver that utilizes two injection-locked oscillator stages to extract the modulation envelope and phase components of a received nonconstant envelope modulation signal without using phase-locked-loop-based carrier recovery circuitry is presented. The paper begins with a theoretical analysis of injection locking and pulling phenomena based on the discrete-time computation approach, and then develops the principles of the proposed receiver. The implemented prototype can cover a sensing bandwidth of 140 MHz at a central frequency of 2.43 GHz and perform π/4 differential quadrature phase-shift keying and quadrature phase-shift keying demodulation with the best error vector magnitudes of 6.6% and 7.9%, respectively, both at a symbol rate of 2 Ms/s. Due to its simplicity, the proposed receiver has great potential as an energy-efficient architecture with low complexity for short-range wireless communications.

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.

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.

Wireless polar receiver using two injection-locked oscillator stages for green radios

Direct-conversion receiver is the most prevalent receiver architecture today for wireless communications. However, it requires coherent demodulation using the phase-locked loop (PLL)-based carrier recovery techniques, which increases circuit complexity and power consumption of the receiver. This paper presents a novel polar receiver that utilizes two injection-locked oscillators (ILO) stages to extract the modulation envelope and phase components from a received non-constant envelope modulation signal without using carrier recovery circuitry. The implemented prototype can perform π/4 DQPSK and QPSK demodulation with error vector magnitudes (EVM) of 7.5% and 8.2%, respectively, both at 2 Msps and a received power of −40 dBm. Owing to its simplicity, the proposed receiver has great potential as an energy-efficient architecture with low cost for green radio applications.

Design of a Direct Conversion Transmitter to Resist Combined Effects of Power Amplifier Distortion and Local Oscillator Pulling

This work elucidates how the combined effects of power-amplifier distortion and local-oscillator (LO) pulling adversely impact a wireless direct-conversion transmitter (DCT) that adopts a time-varying envelope modulation. An analytical model is developed to evaluate the deterioration of DCT output signal quality, including error vector magnitude, adjacent channel power ratio, and spectral regrowth. Additionally, an integrated approach for PA linearization and anti-LO pulling is designed based on an open-loop digital-predistortion method and the proposed analog feedback compensation mechanism. Experimental results demonstrate that a quadrature-modulation-based DCT that incorporates the proposed approaches can significantly improve the LO spectral purity, while achieving a high linearity and efficiency performance simultaneously. These attributes are highly desired for third-generation systems such as cdma2000 1x and W-CDMA.

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.

Direct-conversion transmitter with resistance to local oscillator pulling in non-constant envelope modulation systems

This paper studies the local oscillator (LO) pulling problems associated with a direct-conversion transmitter (DCT) that uses non-constant envelope modulation schemes. The relevant theory provides a time-domain LO model with a modulated outer self-injection to predict the phase fluctuation of an LO that is pulled by the transmitters modulated output signal. Based on a theoretical analysis, the proposed model can be used to evaluate the degraded quality of the transmission signal in terms of error vector magnitude (EVM) and adjacent channel power ratio (ACPR). To mitigate the effects of LO pulling, a novel approach for reducing the AM-FM and PM-FM distortions by a combination of second-point VCO modulation and inner self-injection is proposed. The improved performance is verified by implementing a Quadrature-Phase-Shift-Keying (QPSK) transmitter for cdma2000 1× applications. The theoretical and experimental results agree closely with each other.

A low-noise CMOS frequency synthesizer with an ultra-short settling time

In this work, a novel self-injection-locked (SIL) loop is incorporated into a CMOS frequency synthesizer for fast frequency switching. The proposed SIL loop is based on an injection-locked oscillator (ILO) which behaves as an active delay unit to suppress the excess phase noise produced owing to the large phase-locked loop (PLL) bandwidth. Consequently, the synthesizer with the ILO-based SIL loop can achieve an ultrashort settling time of 2.3 μs and simultaneously a low phase noise of -123 dBc/Hz at 1 MHz offset frequency.