An IF-sampling SC complex lowpass ΣΔ modulator with high image rejection by capacitor sharing

Author

Cheng, W.T. ; Pun, K.P. ; Chan, C.F. ; Choy, C.S.

Author_Institution

Dept. of Electron. Eng., Chinese Univ. of Hong Kong, China

Volume

1

fYear

2004

fDate

23-26 May 2004

Abstract

Lowpass complex sigma-delta (ΣΔ) modulators that have a built-in mixer can be used to digitize narrowband intermediate frequency (IF) signals in radios and cellular systems. A well-known problem of the complex modulators is the mismatches between the in-phase (I) and quadrature phase (Q) channels. In this paper, a technique of sharing the critical sampling and feedback capacitors between the I and Q channels of the modulator is proposed. As demonstrated by circuit simulations, the mismatch effect can be greatly suppressed and thus the image rejection performance can be improved. A 3^rd order complex modulator is designed with a 0.35μm CMOS technology for a 10.7MHz IF input.

Keywords

CMOS integrated circuits; capacitors; circuit simulation; mixers (circuits); sigma-delta modulation; 0.35 micron; 10.7 MHz; CMOS technology; IF-sampling; capacitor sharing; cellular systems; circuit simulations; complex modulators; feedback capacitors; image rejection performance; in-phase channels; lowpass ΣΔ modulator; mismatch effect; mixer; narrowband IF signals; quadrature phase channels; CMOS technology; Capacitors; Delta-sigma modulation; Digital modulation; Feedback; Frequency; Image sampling; Narrowband; Phase modulation; RF signals;

fLanguage

English

Publisher

ieee

Conference_Titel

Circuits and Systems, 2004. ISCAS '04. Proceedings of the 2004 International Symposium on

Print_ISBN

0-7803-8251-X

Type

conf

DOI

10.1109/ISCAS.2004.1328401

Filename

1328401