A GFSK Transmitter Architecture for a Bluetooth RF-IC, Featuring a Variable-Loop-Bandwidth Phase-Locked Loop Modulator

Masaru KOKUBO  Takashi OSHIMA  Katsumi YAMAMOTO  Kunio TAKAYASU  Yoshiyuki EZUMI  Shinya AIZAWA  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E88-C   No.3   pp.385-394
Publication Date: 2005/03/01
Online ISSN: 
DOI: 10.1093/ietele/e88-c.3.385
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Microwaves, Millimeter-Waves
Keyword: 
FSK,  modulator,  delta-sigma,  PLL,  variable loop bandwidth,  Bluetooth,  

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Summary: 
The use of a two-point modulator with variable PLL loop bandwidth as a GFSK signal generator is proposed. Delta-sigma modulation is adopted for the modulator. Through the combination of a variable PLL feedback loop and delta-sigma modulation, both a fast settling time and very clear eye opening are achieved for the modulator. We fabricate it in 0.35-µm BiCMOS process technology. The two-point modulator has a center-frequency drift of only 14.9 kHz, much lower than the 178-kHz result for a single time slot in the case of direct VCO modulation. This is due to the PLL feedback loop. Evaluation also confirmed that the circuit satisfies the various characteristics required of a Bluetooth transmitter. The two-point modulator is also applicable to other transceivers which use FSK or PSK modulation, i.e. forms of modulation where a constant signal level is transmitted, and thus contributes to the simplification of a range of wireless transmitters.