Title :
Direct-conversion transmitter with resistance to local oscillator pulling in non-constant envelope modulation systems
Author :
Hsiao, Chieh-Hsun ; Chen, Chi-Tsan ; Horng, Tzyy-Sheng ; Peng, Kang-Chun
Author_Institution :
Dept. of Electr. Eng., Nat. Sun Yat-Sen Univ., Kaohsiung, Taiwan
Abstract :
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 transmitter´s 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 cdma 2000 1× applications. The theoretical and experimental results agree closely with each other.
Keywords :
amplitude modulation; distortion; frequency shift keying; phase modulation; time-domain analysis; transmitters; voltage-controlled oscillators; AM-FM distortion reduction; PM-FM distortion reduction; QPSK transmitter; adjacent channel power ratio; direct-conversion transmitter; error vector magnitude; local oscillator pulling problem; nonconstant envelope modulation system; phase fluctuation; quadrature phase shift keying; second-point VCO modulation; time-domain LO model; transmission signal; Discrete cosine transforms; Distortion; Frequency modulation; Transmitters; Voltage-controlled oscillators; AM-FM distortion; Direct-conversion transmitter (DCT); PM-FM distortion; local oscillator (LO) pulling; transmit signal quality;
Conference_Titel :
Microwave Symposium Digest (MTT), 2011 IEEE MTT-S International
Conference_Location :
Baltimore, MD
Print_ISBN :
978-1-61284-754-2
Electronic_ISBN :
0149-645X
DOI :
10.1109/MWSYM.2011.5972748