Design and implementation of low phase noise VCO for power aware frequency synthesizer

Abstract

In this dissertation, the concept of power aware optimization is proposed for designing multi-standard frequency synthesizer based on phase-locked loop in a single chip. To prove the proposed concept, a multi-standard frequency synthesizer based on PLL (FS-PLL) is designed for Bluetooth, Zigbee (802.15.4), and WLAN (802.11b) at 2.4 GHz ISM band as a test-bed. Simulated results show that specifications for each standard are satisfied without any degradation of figure of merit (FOM) such as power consumption and silicon area. Each building block of the proposed FS-PLL is designed as follows. A fully differential charge pump is designed having small UP/DN current mismatches and its current is controlled by the constraint of pass-band noise specification. A modified dual path loop filter is proposed to reduce the component size by almost twenty times compared to counterparts of the conventional structure. This alleviates silicon area concerns helping us to easily integrate a loop filter in a single chip. To ensure the wide variation of phase noise, the power consumption of VCO is controlled by a MOS switched tail current source from 1 mW to 18 mW corresponding to 13 dB phase noise difference. Thus, the designed VCO maintains almost constant FOM over the range of its power consumption. That is the ultimate goal of this thesis so-called the concept of power aware optimization. In addition, it is found that an optimum current mirror ratio between the VCO core and the bias circuit exists for low phase noise under a fixed current budget. Contrary to the conventional beliefs that current in the VCO must be maximized for low phase noise, it is shown that the designers must be careful of the current allocation in current mirror to minimize the phase noise. The fabricated VCO has 3~4 dB higher FOM compared to the um-optimized VCO. This is another useful optimization method for achieving a low phase noise VCO in a given current budget. In particular, for narrow channel...