Abstract
In RF transceivers, frequency synthesizers provide a precise local oscillation signal for up and down conversions. The VCO plays an important role in a synthesizer, which copy stable crystal oscillation signal to high frequency range through the negative feedback. The noise behavior of a frequency synthesizer is dominated by the VCO. In tradition designs, a VCO with high analog tuning gain is often used, which results in high phase noise.In this thesis, a novel digitalized VCO is designed for IEEE 802.11a WLAN operation band. The LC-tank topology with an on-chip spiral inductor is applied. Digital varactor arrays substitutes for the conventional connection of capacitors and MOS switches to raise the resolution. Also, the counter, comparator and binary search machine constitute the VCO control circuitry which forms a self-calibration loop with a fractional-N frequency divider to lock accurate states of digital varactors. An experimental chip fabricated by UMC 0.18um CMOS process has been used to demonstrate the circuit performance. The measured oscillation frequency is around 3.8GHz, phase noise is-102dBc/Hz at 1MHz offset and tuning range is 1.7% achieved by the digital varator arrays.