Fully integrated radio over fiber downlink for distributed multi-antenna systems in 65 nm 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 59 dB, and an output referred 1 dB compression point of +6 dBm and an OIP3 of +17 dBm are measured. The SFDR of the circuit is 96.5 dB·Hz^2/3. The phase noise of the PLL measured at 4.2 GHz is -145 dBc/Hz at 20 MHz offset, where as the reference spur level is -58 dBc. The circuit is fabricated in a standard 65 nm CMOS process and occupies just 0.8 mm² of chip area including bond pads.