A Fully Integrated Radio-Fiber Interface in 65 nm CMOS Technology

In this work we present a fully integrated Radio-Fiber interface implemented in 65nm CMOS, intended for remote antenna units (RAUs) in distributed antenna systems. To relax the requirements on the optical components, an intermediate frequency (IF) signal (100MHz) is transmitted over the multi-mode fiber, which is then up-converted to 2.2GHz inside the RAU. Local Oscillator (LO) signals to the mixers are generated by an on-chip frequency synthesizer. The measured optical to electrical conversion gain\,(V/W) is 59\,dB, whereas the input referred current noise is 3.5pA/$\sqrt{\mathrm{Hz}}$ and SFDR is 96.5dBHz^2/3. An LO leakage of -40dBc and an image rejection ratio of 43\,dB is measured. The circuit achieves an adjacent channel leakage ratio (ACLR) of -39dB and -41dB, for a 10MHz 32QAM signal at output power of 1dBm, and a 3.84MHz QPSK signal at 4dBm, respectively.