5.6 A 0.68nW/kHz supply-independent Relaxation Oscillator with ±0.49%/V and 96ppm/°C stability

RC Relaxation Oscillators (RxO) are attractive for integrated clock sources compared to LC and ring oscillators (RO), as LC oscillators pose integration challenges and RO designs have limited voltage and temperature (V-T) stability. RxOs generate a clock whose time period (TP) depends only on the timing resistor (R) and capacitor (C). Ideally, TP is independent of V-T; however, most RxOs use a reference voltage (VREF) against which the voltage of C (Vc) is compared. Generating a V-T-independent VREF is non-trivial and causes variations in RxO frequency. A common approach is the use of VDD-independent current sources or band-gap or device-Vt-based VREF [1]. The former are generally high-power options [2] while the latter is subject to process and V-T variations. A correct-by-design approach was adopted in [3] demonstrating VDD-independent operation by cancelling variations through differential sampling of VDD. Further, the power overhead of a supply-independent VREF is overcome by exploiting differential-integrator virtual ground. However, 4V2/R power in the RC tank and high-power VCO increase the energy/cycle.