An integrated 2.5 GHz ΣΔ frequency synthesizer with 5 μs settling and 2 Mb/s closed loop modulation

Abstract

Three radio communication standards that share common performance requirements are gaining momentum. The 802.11 wireless LAN standard, the Bluetooth radio connectivity protocol, and the HomeRF SWAP home networking protocol all specify frequency hopping radios in the 2.4 GHz band using FSK modulation in a 1 MHz bandwidth. These standards require modest radio performance (compared to cellular systems), but demand small size and low cost. This paper describes a CMOS /spl Sigma//spl Delta/ fractional-N (/spl Sigma//spl Delta/FN) frequency synthesizer. In contrast to prior art, its 700 kHz bandwidth type-1 phase-locked loop (PLL) enables sub-5 /spl mu/s frequency hops plus 2- and 4-level digital Gaussian frequency shift keying (GFSK) modulation at 1 or 2 Mb/s.