A DifferentialRingOscillator with up to 35 dBcHz Phase Noise Improving Amplitude Feedback Loop for Ultra Low Power Systems This work presents a novel idea to dynamically control a differential ring oscillators biasing in order to improve the phase noise performance in the ultra low power domain. This proposed feedback system can be flexibly applied on any type of fullydifferential ring oscillator with a tail current source. The following paper covers theoretical and simulative considerations to prove the feasibility of this idea. Finally measurements of a 180 nm standard CMOS integrated prototype system depict the implementability of this idea. A phase noise improvement of up to 35 dBcHz can be observed with an active control loop. Moreover, the tuning range of the implemented ring oscillator is extended by 434% in contrast to fixed bias operation. These values are measured at a minimum oscillation power consumption of 55 pWHz.

A LowPower ComparatorLess Relaxation Oscillator This paper proposes an integrated lowpower relaxation oscillator using a feedback voltage to boost the swing of the capacitor. A conventional comparator is replaced by an inverter chain, and the static power consumption could be greatly reduced. Moreover, the variation on the threshold of the inverter has no affection on the frequency stability. Since the feedback voltage is proportional to the power supply, the capacitor charging and discharging current which is proportional to the power supply is designed to avoid the frequency variation influenced by the supply voltage. The circuit has been designed with 0.18 xc2xb5m CMOS process. The frequency of the oscillator is designed to 190 kHz. The simulation shows that the worst supply sensitivity of the oscillator achieves 0.84%V, the average temperature coefficient of the oscillation frequency is 197 ppmxc2xb0C, and the power consumption is 2.4 xc2xb5W.