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

In this letter, we present a fully integrated radio-fiber interface implemented in 65-nm CMOS, intended for remote antenna units (RAUs) in distributed antenna systems. To relax the requirements on the optical components, an intermediate frequency signal (100 MHz) is transmitted over the multimode fiber, which is then up-converted to 2.2 GHz 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 3.5 pA/√{Hz} and SFDR is 96.5 dB· Hz^2/3. An LO leakage of -40 dBc and an image rejection ratio of 43 dB is measured. The circuit achieves an adjacent channel leakage ratio of -39 and -41 dB, for a 10-MHz 32 quadrature amplitude modulation signal at output power of 1 dBm, and a 3.84-MHz quadrature phase shift keying signal at 4 dBm, respectively.