Investigation of injection‐locked ring oscillators for process, voltage, and temperature‐aware low phase‐noise reference clock generation

Abstract

In this paper, injection-locked coupled ring oscillators (ROs) are studied regarding their capabilities for process, voltage, and temperature (PVT) compensated reference clock generation. A PVT resilient RO is implemented by means of injection-locked coupled ROs where the injection locking mechanism is realized by employing adjustable coupling factors. It is shown that the oscillation frequency can be highly compensated for temperature-related variations through the coupling factors. In addition, it is possible to compensate the center oscillation frequency for process-induced variations and supply voltage fluctuations. The proposed technique is fully open loop without any frequency tracking loop and can be easily adopted by other architectures of oscillators such as RC and LC counterparts. A 2.4 GHz reference clock generator is implemented in a 0.18 μm standard CMOS process. While the temperature coefficient (TC) of the free-running ROs is about 640 ppm/°C, the coupled structure offers a TC of 80 ppm/°C. Furthermore, the phase-noise of the coupled structure is about 4 dB lower compared with the free-running ROs. The proposed RO consumes about 2.8 mW and occupies a silicon area of 0.09 mm2.