An FMDLL based dual-loop frequency synthesizer for 5 GHz WLAN applications

We present a new dual-loop frequency synthesizer for 5 GHz wireless local-area network (WLAN) applications. In line with the IEEE 802.11a standard, the output frequency is targeted at 5.15 GHz to 5.35 GHz, with a frequency step of 5 MHz. To make the use of the ring-type VCO feasible for this application, we adopted a dual-loop frequency synthesizer architecture similar to that of T. Aytur and J. Khoury (see IEEE Int. Symp. Circuits and Systems, p.17-20, 1997). However, it is critical that the primary loop of such a dual-loop frequency synthesizer is supported by a low-noise reference (by the peripheral loop). To address this problem, we propose a new fractional frequency multiplying delay-locked loop (FMDLL) working as the peripheral loop. MATLAB simulation results demonstrate the phase noise improvement by the use of the proposed FMDLL compared to the conventional design.