Title :
A GMSK modulator using a ΔΣ frequency discriminator-based synthesizer
Author :
Bax, Walter T. ; Copeland, Miles A.
Author_Institution :
SiGe Semicond., Ottawa, Ont., Canada
fDate :
8/1/2001 12:00:00 AM
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;
Journal_Title :
Solid-State Circuits, IEEE Journal of
