Linearity Enhancement for Inverter-Based Optical Receivers Employing Active Feedback

The nonlinearity of optical receivers mainly depends on the final stages of the main amplifier. The Cherry-Hooper (CH) amplifier is popular due to its broad bandwidth. However, CH amplifiers may not offer sufficient linearity, especially for P AM-4 optical links. Previously, the authors designed a highly linear PAM-4 optical receiver using <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$g_{m}/g_{m}$</tex> inverter-based amplifiers known for their superior linearity. To compensate for the lower bandwidth of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$g_{m}/g_{m}$</tex> amplifiers, the interleaving active feedback (IAFB) technique was applied. However, for sub-maximal input voltage amplitudes, the previously proposed design did not give superior linearity over the open-loop structure without IAFB. This paper addresses this issue by modifying the active feedback loops using voltage dividers. Our proposed design operates at a 50 Gb/s data rate with a 1 V supply and achieves a total harmonic distortion (THD) of less than 0.6% for a 500 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{mV}_{\mathrm{P}\mathrm{P}}$</tex> output swing.