Ultra low voltage, wide tuning range voltage controlled ring oscillator

An ultra low voltage, wide tuning range voltage controlled ring oscillator is presented in this paper. The threshold voltage of PMOS and NMOS transistors is reduced by forward biasing the bulk junction of the transistors for ultra low power supply voltage operation. The linearity of four different PMOS loading architectures is compared and the PMOS load with best linearity is used in the proposed delay cell. The frequency of the VCO is tuned by changing the resistance of the loading transistors. A tree stage voltage controlled ring oscillator VCO is designed in 0.18 μm RF CMOS process. The frequency of the proposed VCO is changed from 82 MHz to 370 MHz when the control voltage is from 0.5 V to 0 V. The phase noise of the VCO is -82dBc/Hz at 1MHz offset frequency when it oscillates at 370MHz.