A 2.7-GHz digitally-controlled ring oscillator with supply sensitivity of 0.0014%-fDCO/1%-VDD using digital current-regulated tuning

A method to reduce the supply voltage sensitivity of digitally-controlled ring oscillators (DCROs) using digital current-regulated tuning is presented. By regulating the supply current of ring oscillator instead of its supply voltage, the proposed technique overcomes the limitations of conventional voltage regulator, achieves high supply-noise rejection performance and digital tuning of current-regulated DCRO. The proposed DCRO system implemented in a 0.13-μm CMOS process operates from 1.8 to 3.7 GHz. At 2.7 GHz, the current-regulated DCRO achieves static and dynamic supply-noise immunity of 0.0006%-f_OUT/1%-V_DD and 0.0014%-f_OUT/1%-V_DD respectively, while employing a 150-pF decoupling capacitor, and consuming 1.7 mW from a 1.2 V supply.