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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
IEICE TRANSACTIONS on Electronics
Publication Date: 2005/03/01
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Microwaves, Millimeter-Waves
FSK, modulator, delta-sigma, PLL, variable loop bandwidth, Bluetooth,
Full Text: PDF(1.7MB)>>
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.