A Free-Space Optically Locked VCO With Picosecond Timing Jitter in 0.18- m CMOS

In this letter, we present a novel receiver for time transfer that achieves picosecond accuracy through a line-of-sight link. The receiver is based on a fully integrated optically locked voltage controlled oscillator (OL-VCO) and is implemented in a commercial CMOS process. The design of optical photodiodes integrated with the OL-VCO is explained in detail. It is demonstrated that in the locked mode, the OL-VCO can be synchronized with a 1.3-GHz RF source through a free-space optical link. The free-space synchronization improves the phase noise of the OL-VCO by 25 dB at 100-Hz offset frequency. It is shown that a time transfer accuracy of picosecond can be achieved over a distance of 1.5 m. This represents more than two orders of magnitude improvement compared with the prior art.