Analysis and Design of a Core-Size-Scalable Low Phase Noise <i>LC</i>-VCO for Multi-Standard Cellular Transceivers

Abstract

A core-size-scalable LC-voltage-controlled oscillator (VCO) for multi-standard cellular transceivers was fabricated in a 65-nm CMOS process. Theoretical analysis showed that when core current is small a VCO with a larger core-size can achieve lower phase noise. However, when core current is large, a VCO with a smaller core-size can lower phase noise. Based on the analysis, the effective core-size of the VCO was designed to be scalable according to the core current, by switching the secondary core-transistors on or off. Thus, the proposed VCO becomes adaptive to multi-standard cellular transceivers. By turning on the switch, the VCO can operate in the low power (LP) mode for standards that require moderate phase noise in a tight power budget. On the other hand, by turning off the switch, the VCO can operate in the low noise (LN) mode for standards that demand stringent phase noise in a relaxed power budget. When the core current is set to 4 mA, the VCO in the LP mode achieved the phase noise of -127.9 dBc/Hz at the 3 MHz offset from 3.3-GHz signals. When the core current was set to 15 mA, phase noise of the VCO in the LN mode was minimized to -137.5 dBc/Hz at the same offset. The figure of merit (FOM) was -184.8 and -186.5 dB, respectively.