Cancellation for Asymmetrical Waveform in 1-bit Bandpass Delta-Sigma Modulators

Takashi MAEHATA  Suguru KAMEDA  Noriharu SUEMATSU  

Publication
IEICE TRANSACTIONS on Communications   Vol.E100-B   No.6   pp.1017-1022
Publication Date: 2017/06/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.2016EBP3178
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
Keyword: 
delta sigma modulation,  bandpass,  intersymbol interference,  compensation,  digital transmitter,  

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Summary: 
The 1-bit band-pass delta-sigma modulator (BP-DSM) achieves high resolution by using the oversampling technique. This method allows direct RF signal transmission from a digitally modulated signal, using a 1-bit digital pulse train. However, it has been previously reported that the adjacent channel leakage ratio (ACLR) in a target frequency band degrades due to the pulse transition mismatch between rising and falling waveforms in the time domain. This paper clarifies that the spurious distortion in BP-DSM is caused by the asymmetricity of the waveform about the center of an eye pattern in the time axis, and proposes a 1-bit BP-DSM with the compensator consisting of a fractional delay filter and a binary data differentiator to cancel out the asymmetry in the target frequency band. This can accurately provide a wideband cancellation signal with more than 100MHz bandwidth, including the adjacent channel, within 50dB power dynamic range. Using long term evolution (LTE) signals with 5MHz bandwidth at 0.8GHz, we simulated the spurious distortion, performing various combinations of rising and falling times in the eye pattern, and the proposed 1-bit BP-DSM always achieved high ACLR, up to 60dB, in 140MHz bandwidth, under all conditions.