Analysis of Phase Locked Loops with Enhanced Loop Bandwidth

The Phase-Locked Loop is an important building block in wireless transceivers, where it is used to synthesize wireless carriers and clocks. Strict phase noise requirements on the Phase- Locked Loop requires either a high-frequency reference or a high-quality Voltage-Controlled Oscillator. This work presents a new Phase-Locked Loop architecture that makes it possible to have a larger loop-bandwidth with respect to the reference frequency than conventional Phase-Locked Loops. As a result, noisy ring-oscillators and low-frequency reference crystals can be used while still achieving good phase noise performance. An LPTV model and an event-based simulation environment are built to analyze the system's behavior and key performance aspects. As a proof-of-concept, a system-level design of a fractional-N Phase-Locked Loop is presented which meets the Bluetooth Low-Energy requirements while using a cheap, low-power ring- oscillator. The loop has a bandwidth of 10 MHz, while a 20 MHz crystal reference is used. The Phase-Locked Loop exhibits an in-band phase noise of -104 dBc/Hz and has reference spurs less than -100 dBc.