A Novel 16-bit CMOS Digitally Controlled Oscillator

A novel 16-bit CMOS digitally controlled oscillator (DCO) is described. This CMOS DCO design is based on a delay programmable differential latch which yields improved phase noise characteristics. Simulations of a 4-stage CMOS DCO using a 0.5 mum Agilent CMOS process parameters achieved a controllable frequency range of 750MHz - 1.6GHz with a monotone tuning range of around 1GHz. Monte Carlo simulations indicate that the time-period jitter due to random supply voltage fluctuations is under 250ps for worst-case considerations. Also, phase noise was found to be in the range of -175dBc @ a frequency of 600KHz from the carrier at 1.5GHz (for digital control word of 1512H) after numerous iterations of Monte Carlo simulations. FFT analysis indicate a THD (total harmonic distortion) of around -57dB for the DCO output signal. Experimental fabrication using the Agilent 0.5mum 3M1P CMOS process technology was used for the verification of the functional operation of the DCO. This CMOS design would thus provide considerable performance enhancement in digital PLL applications