A 112-Gb/s PAM-4 Optical Receiver With Sub-1.9- μA _rms Noise and <4% THD for Linear-Drive Pluggable Optics

This letter presents a 4 × 112 Gb/s optical receiver with low noise and high output swing for linear-drive pluggable optics (LPOs). The receiver is implemented in 0.13-μm SiGe-BiCMOS technology with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>T</roman></sub>/<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>MAX</roman></sub> = 260/350 GHz. An inductive shunt-feedback (ISFB) transimpedance stage (TIS) employing π-topology <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> network is positioned as an input stage of optical receiver. This design achieves a wide bandwidth (BW) and low noise simultaneously, despite large photograph diode (PD) and packaging parasitic capacitance. Two current-splitting variable gain amplifiers (VGAs) with continuous-time linear equalizer (CTLE) function cascaded after TIS. These VGAs feature high reliability, compensate for BW loss, and provide a gain control range of -12 dB~+18 dB, accommodating input current up to 2 mA<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>pp</roman></sub>. The measurement results show that optical receiver provides a maximum O/E transimpedance gain (O/E.<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>T</roman></sub>) of 73.8 dBΩ with O/E.BW beyond 35 GHz, an input-referred noise (IRN) current of 1.9 μA<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>rms</roman></sub>, and the total harmonic distortion (THD) < 4% for 600-mVpp output swing. The proposed optical receiver operates PAM-4 eye diagrams up to 56-Gbaud using PRBS31Q and exhibits an optical modulation amplitude (OMA) sensitivity of -9 dBm at pre-FEC bit error rate (BER) limit of 2 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> with 56-Gbaud PAM-4 SSPRQ. The optical receiver achieves a power efficiency of 1.65-pJ/bit and occupies an area of 3.14 × 1.04 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>.