600 MHz digitally controlled BiCMOS oscillator (DCO) for VLSI signal processing and communication applications

A 16-bit digitally controlled BiCMOS ring oscillator (DCO) is described. This BiCMOS DCO design provides improved frequency stability under thermal fluctuations. Simulations of a 5-stage DCO using 1 μm BiCMOS process parameters achieved controllable frequency range of 90-640 MHz with a linear/quasi-linear range of around 300 MHz. Monotone frequency gain (frequency vs control-word transfer function) with fine stepping (tuning) in several KHz was verified This augurs the prospect of accurate frequency lock in a BiCMOS all digital PLL (ADPLL) application in digital VLSI communication systems. Worstcase jitter due to digital control transitions at pathological control-word boundaries for the BiCMOS DCO was observed to be less than 50 ps, which is lower than that for the CMOS DCO