A clip-and-restore technique for phase desensitization in a 1.2V 65nm CMOS oscillator for cellular mobile and base stations

Base-station (BTS) RX oscillator phase noise requirements between 600kHz and 3MHz are difficult to satisfy using a fully monolithic VCO fabricated in bulk-CMOS technology. The GSM-900-BTS and the DCS-1800-BTS RX specifications at 800kHz of -147dBc/Hz and -138dBc/Hz, respectively, are considered the most difficult to meet. In GSM mobile stations (MS), the transmit and receive bands are 20MHz apart, which sets a stringent TX phase noise requirement of -162dBc/Hz at 20MHz offset [1]. A VCO satisfying this inadvertently meets the relatively relaxed RX specification.