Capacitive Degeneration in LC-Tank Oscillator for DCO Fine-Frequency Tuning

A digitally controlled oscillator (DCO) that achieves a minimum frequency quantization step of 150 Hz without any dithering is presented. The fine digital tuning is obtained through a capacitive degeneration of a portion of the transistor switching pair used in a classical LC-tank oscillator. The new tuning circuitry does not appreciably affect the intrinsic oscillator phase noise and allows to trim the frequency with a programmable resolution for calibration and multi-standard operation. A prototype integrated in 65 nm CMOS technology exhibits a phase noise of -127.5 dBc/Hz @ 1 MHz drawing 16 mA from a supply of 1.8 V, resulting in a FoM of 183 dBc/Hz. The active area is 700 mu m x 450 mu m.