Design of automatic frequency calibration Used in the PLL frequency synthesizer for 2.4GHz WSN

In this paper, an open looped fast automatic frequency calibration (AFC) unit used in 2.4GHz CMOS integer-N phase-locked loop (PLL) frequency synthesizer (FS) for IEEE802.15.4/ZigBee wireless sensor networks (WSN) is presented. The calibration method accomplishes efficient search for an optimum discrete tuning curve of the voltage controlled oscillator (VCO) among a group of frequency sub-bands. The pre-simulation, layout design and post-simulation results are given. Post simulation results show that the AFC performs well.