A 3-Tap FIR Filter With Cascaded Distributed Tap Amplifiers for Equalization Up to 40 Gb/s in 0.18- m CMOS

This paper describes a 3-tap finite impulse response programmable analog filter in 0.18-mum CMOS. The filter is intended for polarization-mode dispersion compensation in 40-Gb/s long-haul single-mode optical fiber links. A novel filter topology is employed, whereby each tap gain comprises a cascade of two distributed amplifiers with adjustable gain. The same lumped LC ladders that provide the 25-ps tap delays also serve as artificial transmission lines for the distributed tap amplifiers. The prototype is 1 mm times 1 mm (900 mumtimes600 mum active area) and consumes up to 70 mW from a 1.8-V supply depending on the tap gains. Linear equalization is demonstrated over a channel with 17 dB of loss at 20 GHz. A 50 mV per side eye amplitude with 14 dB signal-to-noise ratio is demonstrated at 30 Gb/s, and a modest 39 mV per side eye amplitude with 10 dB signal-to-noise ratio is achieved at 40 Gb/s