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A 2.4-GHz monolithic fractional-N frequency synthesizer with robust phase-switching prescaler and loop capacitance multiplier
Keliu Shu; Sanchez-Sinencio, E.; Silva-Martinez, J.; Embabi, S.H.K.;
Solid-State Circuits, IEEE Journal of
Volume 38,
Issue 6,
June 2003
Page(s):866
-
874
Abstract:
The design of a 2.4-GHz fully integrated ΣΔ fractional-N frequency synthesizer in a 0.35-μm CMOS process is presented. The design focuses on the prescaler and the loop filter, which are often the speed and the integration bottlenecks of the phase-locked loop (PLL), respectively. A 1.5-V 3-mW inherently glitch-free phase-switching prescaler is proposed. It is based on eight lower frequency 45°-spaced phases and a reversed phase-switching sequence. The large integrating capacitor in the loop filter was integrated on chip via a simple capacitance multiplier that saves silicon area, consumes only 0.2 mW, and introduces negligible noise. The synthesizer has a 9.4% frequency tuning range from 2.23 to 2.45 GHz. It dissipates 16 mW and takes an active area of 0.35 mm2 excluding the 0.5-mm2 digital ΣΔ modulator.
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