CMOS digitally programmable quadrature oscillators

CMOS digitally programmable quadrature oscillators based on digitally controlled current followers and voltage followers are proposed. The proposed designs provide the advantage of programmability similar to the operational transconductance amplifier-based oscillators while offering improved linearity. In mixed analog/digital systems, the digital tuning feature allows direct interfacing with the digital signal processing part. Novel realizations that provide both voltage-mode and current-mode quadrature sinusoidal signals are presented. Employing only grounded capacitors the designs achieve independent control of the frequency and condition of oscillation that can be tuned digitally. Experimental results obtained from a 0.35 μm CMOS chip fabricated using standard CMOS process are given.