A GMSK modulator using a ΔΣ frequency discriminator-based synthesizer

Author

Bax, Walter T. ; Copeland, Miles A.

Author_Institution

SiGe Semicond., Ottawa, Ont., Canada

Volume

36

Issue

8

fYear

2001

fDate

8/1/2001 12:00:00 AM

Firstpage

1218

Lastpage

1227

Abstract

This paper describes a new transmitter architecture suitable for wideband GMSK modulation. The technique uses direct modulation of ΔΣ frequency discriminator (ΔΣFD)-based synthesizer to produce the modulated RF signal without any up-conversion. Digital equalization is used to extend the modulation data rate far beyond the synthesizer closed-loop BW. A prototype 1.9-GHz GSM transmitter was constructed consisting of a ΔΣFD-based synthesizer and a digital transmit filter. The synthesizer consists of an 0.8-μm BiCMOS ΔΣFD chip, a digital signal processor FPGA, and an off-chip D/A converter, filter, and VCO. Measured results, using 271-kbit/s GSM modulation, demonstrate data rates well in excess of the 30-kHz synthesizer closed-loop BW are possible with digital equalization. Without modulation, the synthesizer exhibits a -76-dBc spurious noise level and a close-in phase noise of -74 dBc/Hz

Keywords

BiCMOS digital integrated circuits; continuous phase modulation; delta-sigma modulation; digital phase locked loops; digital radio; discriminators; field programmable gate arrays; frequency synthesizers; minimum shift keying; mobile radio; modulators; phase noise; quantisation (signal); radio transmitters; 1.9 GHz; 271 kbit/s; BiCMOS chip; DSP FPGA; GSM modulation; VCO; continuous phase modulation; delta-sigma frequency discriminator-based synthesizer; digital equalization; digital transmit filter; direct modulation; modulated RF signal; off-chip D/A converter; phase noise; phase-frequency detector; quantisation; transmitter architecture; wideband GMSK modulation; BiCMOS integrated circuits; Delta modulation; Digital filters; Digital modulation; Frequency modulation; Frequency synthesizers; GSM; Prototypes; Transmitters; Wideband;

fLanguage

English

Journal_Title

Solid-State Circuits, IEEE Journal of

Publisher

ieee

ISSN

0018-9200

Type

jour

DOI

10.1109/4.938372

Filename

938372