A 1.7-mW 26.5-GHz LC-DCO with Optimum-Q Varactors for 25-Gb/s Automotive Optical Links

This paper presents the design of a 26.5-GHz LC-DCO for a Multi-Gigabit automotive optical transceiver compatible with the recently published IEEE 802.3cz standard. Digital-controlled varactors are frequently used to implement frequency control by means of a digital processor, allowing high re-configurability and adaptability of the system. An optimum design of these oscillators requires maximizing the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Q$</tex> factor of both the varactor and inductor structures, where all the parasitic components must be taken into account during the design phase. In order to achieve an optimum design in terms of power and performance, this work presents a conscientious analysis to implement an optimized combination of varactor array and inductor, taking into account their parasitic effects in the design flow of an LC-DCO. The LC-DCO has been manufactured using a standard 28-nm bulk-CMOS process. The oscillator exhibits a maximum phase noise of −97.1 dBc/Hz at 1-MHz offset with a power consumption of only 1.7 mW at 1-V supply. The resulting FOM is −183.3 dBc/Hz.