DC offset and IM2 removal in direct conversion receivers

Author

Faulkner, M.

Author_Institution

Centre for Telecommun. & Microelectron., Victoria Univ. of Technol., Melbourne, Vic., Australia

Volume

149

Issue

3

fYear

2002

fDate

6/1/2002 12:00:00 AM

Firstpage

179

Lastpage

184

Abstract

DC offsets cause interference in homodyne receivers, caused by nonlinearity and imbalances in the receiving amplifier and mixing circuits, as well as local oscillator (LO) leakage into the RF input port and RF leakage into the LO port. The latter causes a squaring action (hence, second order intermodulation distortion (IM2)) in the mixer which generates a DC offset (low frequency) that varies with the amplitude of any high power RF interfering (jamming) signal, whatever its applied frequency. A method for removing this DC offset is described. The signal immediately after the mixer is squared to obtain a distortion estimate of the jamming signal, and then subtracted from the main signal path to remove the interference from the desired signal. The experimental results indicate an 11.5 dB improvement in jamming margin for systems with 30 kHz RF bandwidth. In the experiment an adaptive equaliser is used to equalise the two paths and improve the dynamic response

Keywords

adaptive equalisers; cellular radio; interference suppression; intermodulation distortion; jamming; radio receivers; DC offset; GSM systems; IM2 removal; LO port; RF input port; RF leakage; RFI; adaptive equaliser; amplifier nonlinearity; bandwidth; direct conversion receivers; dynamic response; high power RF interfering signal; homodyne receivers; interference; jamming margin; jamming signal; local oscillator leakage; mixing circuits; second order intermodulation distortion;

fLanguage

English

Journal_Title

Communications, IEE Proceedings-

Publisher

iet

ISSN

1350-2425

Type

jour

DOI

10.1049/ip-com:20020263

Filename

1024734