Low-EVM CMOS Transimpedance Amplifier for Intermediate Frequency over Fiber

A highly-linear low-noise transimpedance amplifier (TIA) with programmable gain for intermediate frequency-over-fiber (IFoF) communications is presented in this paper. It has been fabricated in a 65-nm RF CMOS technology for use in the downlink receiver of remote antenna units for a cost-effective distributed antenna system. The topology consists of a shunt-shunt feedback TIA with open-loop gain control to ensure constant bandwidth, while the transimpedance can be linear-in-dB programmed from 60 to 76 dBO. The IFoF transmission is achieved with a very low error vector magnitude below 2% over an input dynamic range from -16 dBm up to +4 dBm optical power. The TIA shows an equivalent input noise of 8 pA/√Hz at 500 MHz with a bandwidth of 700 MHz. The TIA presents a power consumption of 6 mW from a single supply voltage of 1.2 V, while the total power consumption including the output driver is 19 mW.