A fully integrated, automatically adjusted CMOS RF modulator for cellular applications

This paper describes a fully integrated RF phase modulator based on a type I fractional-N phase locked loop (PLL). A digital preemphasis filter is used to extend the transfer bandwidth beyond the narrow loop bandwidth. All critical process dependent components like VCO, loop filter and charge pump are controlled and aligned fully digital to provide the necessary accuracy needed for wideband phase modulation. The VCO operates at 4 GHz, with a phase noise of -165 dBc/Hz at 20 MHz offset from the carrier. The phase modulator was implemented in a single chip GSM/GPRS transceiver as well as in a single chip GSM/EDGE polar modulator transceiver.