Chi-Tsan Chen

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.

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.

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.

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.

Kahn envelope elimination and restoration technique using injection-locked oscillators

The envelope elimination and restoration (EER) technique, which was proposed by Kahn, is a recognized means of highly-efficient linear amplification. This paper presents a novel EER transmitter using injection-locked oscillators (ILOs). In the proposed architecture, an ILO that is combined with a mixer and a low-pass filter extracts an envelope signal and a phase-modulated RF signal from an RF input signal with time-varying envelope modulation. Then, the phase-modulated RF signal is efficiently amplified by a Class-E power amplifier (PA) and the envelope signal is restored at the PA output by modulating the supply voltage of the PA. The constructed prototype of the EER transmitter achieves a 21 dB power gain and a 36% power-added efficiency at an average output power of 23 dBm for Enhanced Data rates for GSM Evolution (EDGE) signals, meeting the spectral mask specifications without using any pre-distortion techniques.

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.

Design and linearization of Class-E power amplifier for non-constant 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. A predistorted envelope modulation scheme is proposed to linearize the class-E PA. To accomplish this scheme, the class-E PA is designed with consideration of finite DC-feed inductance for wide supply-voltage modulation bandwidth. In addition, a digital envelope predistorter (DEP) is designed to provide the predistored envelope modulation for both RF-input and supply-voltage signals fed to the class-E PA. A cdma2000 1x transmitter incorporating such a Class-E PA and a DEP has been implemented to serve as an evidence for the simultaneous achievement of high efficiency and high linearity.

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.

High efficiency dual-band Class-E power amplifier design

A design methodology for 1.95 and 2.6 GHz dualband power amplifiers (PA) with high efficiency is presented in this paper. To achieve maximum power added efficiency (PAE), this paper proposes a novel Class-E PA design approach using a multi-level switching resistance model to find the optimum continuous-wave parameters at various input power levels. Consequently, for the designed Class-E PA, the finial measured maximum PAE is 65.8% with an output power of 794 mW at 1.95 GHz, and 63.6% with an output power of 631 mW at 2.6 GHz. The gain at maximum PAE is 8.3 dB and 8.8 dB at 1.95 GHz and 2.6 GHz, respectively.

Power amplifier linearization using baseband digital predistortion for WiMAX applications

The developed baseband digital predistortion successfully linearizes the PA up to its saturated power. The average PA efficiency will expectedly enhance since the PA operates in the higher, more efficient, power region as well as meets the IEEE 802.16d spectrum mask and RCE specification. At the same M-IMR, which is -28.7 dBc, under ten-tone CW measurement, the predistorted PA is 2.9% higher in efficiency than before.