Fully Integrated Radio over Fiber Downlink for Distributed Multi-antenna Systems in 65nm CMOS

This paper presents a fully integrated downlink for low-cost remote antenna units in fiber-fed distributed multi-antenna systems. To reduce the cost of optical parts, an intermediate frequency(IF) signal is distributed over the fiber, and the circuit consists of an optical receiver, a single side-band frequency up-converting radio transmitter, and LO generation circuitry. The optical to electrical conversion gain(V/W) of the system is 59dB, and an output referred 1dB compression point of +6dBm and an OIP3 of +17dBm are measured. The SFDR of the circuit is 96.5 dBHz^2/3. The phase noise of the PLL measured at 4.2GHz is -145dBc/Hz at 20MHz offset, where as the reference spur level is -58dBc. The circuit is fabricated in a standard 65nm CMOS process and occupies just 0.8mm^2 of chip area including bond pads.