Complex Bandpass ΔΣAD Modulator Architecture without I, Q-Path Crossing Layout

Hao SAN  Akira HAYAKAWA  Yoshitaka JINGU  Hiroki WADA  Hiroyuki HAGIWARA  Kazuyuki KOBAYASHI  Haruo KOBAYASHI  Tatsuji MATSUURA  Kouichi YAHAGI  Junya KUDOH  Hideo NAKANE  Masao HOTTA  Toshiro TSUKADA  Koichiro MASHIKO  Atsushi WADA  

Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E89-A   No.4   pp.908-915
Publication Date: 2006/04/01
Online ISSN: 1745-1337
DOI: 10.1093/ietfec/e89-a.4.908
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Selected Papers from the 18th Workshop on Circuits and Systems in Karuizawa)
Category: 
Keyword: 
complex bandpass ΔΣAD modulator,  I,  Q path mismatches,  dynamic matching,  multiplexer,  

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Summary: 
This paper proposes a new architecture for multibit complex bandpass ΔΣAD modulators with built-in Switched-Capacitor (SC) circuits for application to Low-IF receivers such as used for Bluetooth and WLAN. In the realization of complex bandpass ΔΣAD modulators, we face the following problems: (i) SNR of AD converter is deteriorated by mismatches between internal analog I and Q paths. (ii) Layout design becomes complicated because of signal lines crossing by complex filter and feedback from DAC for I and Q paths in the complex modulator, and this increases required chip area. We propose a new structure for a complex bandpass ΔΣAD modulator which can be completely divided into two paths without layout crossing, and solves the problems mentioned above. The two parts of signal paths and circuits in the modulator are changed for I and Q while CLK is changed for High/Low by adding multiplexers. Symmetric circuits are used for I and Q paths at a certain timing, and they are switched by multiplexers to those used for Q and I paths at another timing. Therefore the influence from mismatches between I and Q paths is reduced by dynamic matching. As a result, the modulator is divided into two separate parts without crossing signal lines between I and Q paths and its layout design can be greatly simplified compared with conventional modulators. We have conducted MATLAB simulations to confirm the effectiveness of the proposed structure.